% % This file was created by the Typo3 extension % sevenpack version 0.7.14 % % --- Timezone: CEST % Creation date: 2013-06-20 % Creation time: 07-44-32 % --- Number of references % 54 % @Article { HerdenerESSLUK2013, title = {Spatial representations of temporal and spectral sound cues in human auditory cortex}, journal = {Cortex}, year = {2013}, month = {4}, volume = {Epub ahead}, abstract = {Natural and behaviorally relevant sounds are characterized by temporal modulations of their waveforms, which carry important cues for sound segmentation and communication. Still, there is little consensus as to how this temporal information is represented in auditory cortex. Here, by using functional magnetic resonance imaging (fMRI) optimized for studying the auditory system, we report the existence of a topographically ordered spatial representation of temporal sound modulation rates in human auditory cortex. We found a topographically organized sensitivity within auditory cortex to sounds with varying modulation rates, with enhanced responses to lower modulation rates (2 and 4 Hz) on lateral parts of Heschl's gyrus (HG) and faster modulation rates (16 and 32 Hz) on medial HG. The representation of temporal modulation rates was distinct from the representation of sound frequencies (tonotopy) that was orientated roughly orthogonal. Moreover, the combination of probabilistic anatomical maps with a previously proposed functional delineation of auditory fields revealed that the distinct maps of temporal and spectral sound features both prevail within two presumed primary auditory fields hA1 and hR. Our results reveal a topographically ordered representation of temporal sound cues in human primary auditory cortex that is complementary to maps of spectral cues. They thereby enhance our understanding of the functional parcellation and organization of auditory cortical processing.}, department = {Department Scheffler}, department2 = {Department Logothetis}, department3 = {Research Group Kayser}, web_url = {http://www.sciencedirect.com/science/article/pii/S001094521300110X}, DOI = {10.1016/j.cortex.2013.04.003}, author = {Herdener, M and Esposito, F and Scheffler, K and Schneider, P and Logothetis, NK and Uludag, K and Kayser, C} } @Article { CavusogluPBU2012, title = {Regional effects of magnetization dispersion on quantitative perfusion imaging for pulsed and continuous arterial spin labeling}, journal = {Magnetic Resonance in Medicine}, year = {2013}, month = {2}, volume = {69}, number = {2}, pages = {524–530}, abstract = {Most experiments assume a global transit delay time with blood flowing from the tagging region to the imaging slice in plug flow without any dispersion of the magnetization. However, because of cardiac pulsation, nonuniform cross-sectional flow profile, and complex vessel networks, the transit delay time is not a single value but follows a distribution. In this study, we explored the regional effects of magnetization dispersion on quantitative perfusion imaging for varying transit times within a very large interval from the direct comparison of pulsed, pseudo-continuous, and dual-coil continuous arterial spin labeling encoding schemes. Longer distances between tagging and imaging region typically used for continuous tagging schemes enhance the regional bias on the quantitative cerebral blood flow measurement causing an underestimation up to 37\% when plug flow is assumed as in the standard model.}, department = {Department Scheffler}, web_url = {http://onlinelibrary.wiley.com/doi/10.1002/mrm.24278/pdf}, DOI = {10.1002/mrm.24278}, author = {Cavusoglu, M and Pohmann, R and Burger, HC and Uludag, K} } @Article { CavusogluBYU2011, title = {Retinotopic maps and hemodynamic delays in the human visual cortex measured using arterial spin labeling}, journal = {NeuroImage}, year = {2012}, month = {2}, volume = {59}, number = {4}, pages = {4044–4054}, abstract = {Cortical representations of the visual field are organized retinotopically, such that nearby neurons have receptive fields at nearby locations in the image. Many studies have used blood oxygenation level-dependent (BOLD) fMRI to non-invasively construct retinotopic maps in humans. The accuracy of the maps depends on the spatial extent of the metabolic and hemodynamic changes induced by the neural activity. Several studies using gradient-echo MRI at 1.5 T and 3 T showed that most of the BOLD signal originates from veins, which might lead to a spatial displacement from the actual site of neuronal activation, thus reducing the specificity of the functional localization. In contrast to BOLD signal, cerebral blood flow (CBF) as measured using arterial spin labeling (ASL) is less or not at all affected by remote draining veins, and therefore spatially and temporally more closely linked to the underlying neural activity. In the present study, we determined retinotopic maps in the human brain using CBF as well as using BOLD signal in order to compare their spatial relationship and the temporal delays of each imaging modality for visual areas V1, V2, V3, hV4 and V3AB. We tested the robustness and reproducibility of the maps across different sessions, calculated the overlap as well as signal delay times across visual areas. While area boundaries were relatively well preserved, we found systematic differences of response latencies between CBF and the BOLD signal between areas. In summary, CBF data obtained using ASL allows reliable retinotopic maps to be constructed; this approach is, therefore, suitable for studying visual areas especially in close proximity to large veins where the BOLD signal is spatially inaccurate.}, department = {Department Scheffler}, department2 = {Department Logothetis}, web_url = {http://www.sciencedirect.com/science/article/pii/S1053811911012201}, DOI = {10.1016/j.neuroimage.2011.10.056}, author = {Cavusoglu, M and Bartels, A and Yesilyurt, B and Uludag, K} } @Article { 5939, title = {Relationship of the BOLD signal with VEP for ultrashort duration visual stimuli (0.1 to 5 ms) in humans}, journal = {Journal of Cerebral Blood Flow and Metabolism}, year = {2010}, month = {2}, volume = {30}, number = {2}, pages = {449-458}, abstract = {There is currently a great interest to combine electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) to study brain function. Earlier studies have shown different EEG components to correlate well with the fMRI signal arguing for a complex relationship between both measurements. In this study, using separate EEG and fMRI measurements, we show that (1) 0.1 ms visual stimulation evokes detectable hemodynamic and visual-evoked potential (VEP) responses, (2) the negative VEP deflection at approx80 ms (N2) co-varies with stimulus duration/intensity such as with blood oxygenation level-dependent (BOLD) response; the positive deflection at approx120 ms (P2) does not, and (3) although the N2 VEP–BOLD relationship is approximately linear, deviation is evident at the limit of zero N2 VEP. The latter finding argues that, although EEG and fMRI measurements can co-vary, they reflect partially independent processes in the brain tissue. Finally, it is shown that the stimulus-induced impulse response function (IRF) at 0.1 ms and the intrinsic IRF during rest have different temporal dynamics, possibly due to predominance of neuromodulation during rest as compared with neurotransmission during stimulation. These results extend earlier findings regarding VEP–BOLD coupling and highlight the component- and context-dependency of the relationship between evoked potentials and hemodynamic responses.}, department = {Department Logothetis}, department2 = {Department MRZ}, web_url = {http://www.nature.com/jcbfm/journal/vaop/ncurrent/pdf/jcbfm2009224a.pdf}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, language = {en}, DOI = {10.1038/jcbfm.2009.224}, author = {Yesilyurt, B and Whittingstall, K and Ugurbil, K and Logothetis, NK and Uludag, K} } @Article { 6054, title = {The Cortical Site of Visual Suppression by Transcranial Magnetic Stimulation}, journal = {Cerebral Cortex}, year = {2010}, month = {2}, volume = {20}, number = {2}, pages = {328-338}, abstract = {In visual suppression paradigms, transcranial magnetic stimulation (TMS) applied \verb=~=90 ms after visual stimulus presentation over occipital visual areas can robustly interfere with visual perception, thereby most likely affecting feedback activity from higher areas (Amassian VE, Cracco RQ, Maccabee PJ, Cracco JB, Rudell A, Eberle L. 1989. Suppression of visual perception by magnetic coil stimulation of human occipital cortex. Electroencephalogr Clin Neurophysiol 74:458–462.). It is speculated that the observed effects might stem primarily from the disruption of V1 activity. This hypothesis, although under debate, argues in favor of a special role of V1 in visual awareness. In this study, we combine TMS, functional magnetic resonance imaging, and calculation of the induced electric field to study the neural correlates of visual suppression. For parafoveal visual stimulation in the lower right half of the visual field, area V2d is shown to be the likely TMS target based on its anatomical location close to the sk ull surface. Furthermore, isolated stimulation of area V3 also results in robust visual suppression. Notably, V3 stimulation does not directly affect the feedback from higher visual areas that is relayed mainly via V2 to V1. These findings support the view that intact activity patterns in several early visual areas (rather than merely in V1) are likewise important for the perception of the stimulus.}, department = {Department MRZ}, web_url = {http://cercor.oxfordjournals.org/cgi/reprint/bhp102v1}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, language = {en}, DOI = {10.1093/cercor/bhp102}, author = {Thielscher, A and Reichenbach, A and Ugurbil, K and Uludag, K} } @Article { 6316, title = {To dip or not to dip: Reconciling optical imaging and fMRI data}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, year = {2010}, month = {2}, volume = {107}, number = {6}, pages = {E23}, abstract = {Several optical studies have reported a brief initial increase of deoxyhemoglobin (1), which is consistent with an initial dip observed in the functional MRI (fMRI) signal, evoked by local neuronal activity. This effect is small and not always present (2), but it has stirred great interest because it may reflect a rapid increase of oxidative metabolism before increases in blood flow and, thus, may have a narrower spatial spread than the main positive hemodynamic response. In a recent elegant and comprehensive study, Sirotin et al. (3) investigated the spatiotemporal specificity of intrinsic optical imaging signals at different wavelengths and for different chromophores.}, department = {Department MRZ}, web_url = {http://www.pnas.org/content/107/6/E23.full.pdf+html}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, language = {en}, DOI = {10.1073/pnas.0914194107}, author = {Uludag, K} } @Article { 5929, title = {Interleaved TMS/CASL: Comparison of different rTMS protocols}, journal = {NeuroImage}, year = {2010}, month = {1}, volume = {49}, number = {1}, pages = {612-620}, abstract = {Continuous Arterial Spin Labeling (CASL) offers the possibility to quantitatively measure the regional cerebral blood flow (rCBF). We demonstrate, for the first time, the feasibility of interleaving Transcranial Magnetic Stimulation (TMS) with CASL at 3 T. Two different repetitive TMS (rTMS) protocols were applied to the motor cortex in 10 subjects and the effect on rCBF was measured using a CASL sequence with separate RF coils for labeling the inflowing blood. Each subject was investigated, using a block design, under 7 different conditions: continuous 2 Hz rTMS (3 intensities: 100\%, 110\% and 120\% resting motor threshold [MT]), short 10 Hz rTMS trains at 110\% MT (8 pulses per train; 3 different numbers of trains per block with 2, 4 and 12 s intervals between trains) and volitional movement (acoustically triggered by 50\% MT stimuli). We show robust rCBF increases in motor and premotor areas due to rTMS, even at the lowest stimulation intensity of 100\% MT. RCBF exhibited a linear positive dependency on stimula tion intensity (for continuous 2 Hz rTMS) and the number of 10 Hz trains in the stimulated M1/S1 as well as in premotor and supplementary motor areas. Interestingly, the 2 different rTMS protocols yielded markedly different rCBF activation time courses, which did not correlate with the electromyographic recordings of the muscle responses. In future, this novel combination of TMS with ASL will offer the possibility to investigate the immediate and after-effects of rTMS stimulation on rCBF, which previously was only possible using PET.}, department = {Department MRZ}, web_url = {http://www.sciencedirect.com/science?_ob=MImg\&_imagekey=B6WNP-4WS2HW9-7-K\&_cdi=6968\&_user=29041\&_orig=search\&_coverDate=01\%2F01\%2F2010\&_sk=999509998\&view=c\&wchp=dGLbVtz-zSkzS\&md5=0c07d14134d790e237c2ec8c346cbd77\&ie=/sdarticle.pdf}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, language = {en}, DOI = {10.1016/j.neuroimage.2009.07.010}, author = {Moisa, M and Pohmann, R and Uludag, K and Thielscher, A} } @Article { 5882, title = {An integrative model for neuronal activity-induced signal changes for gradient and spin echo functional imaging}, journal = {NeuroImage}, year = {2009}, month = {10}, volume = {48}, number = {1}, pages = {150-165}, department = {Department MRZ}, web_url = {http://www.sciencedirect.com/science?_ob=PdfDownloadURL\&_uoikey=B6WNP-4WCTWRD-3\&_tockey=\%23toc\%236968\%232009\%23999519998\%231390069\%23FLA\%23\&_orig=browse\&_acct=C000003178\&_version=1\&_userid=29041\&md5=29bff6d1590ff5e43386d8a0bd0a}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, language = {en}, DOI = {10.1016/j.neuroimage.2009.05.051}, author = {Uludag, K and M{\"u}ller-Bierl, B and Ugurbil, K} } @Article { 5689, title = {Comparison of pulsed arterial spin labeling encoding schemes and absolute perfusion quantification}, journal = {Magnetic Resonance Imaging}, year = {2009}, month = {10}, volume = {27}, number = {8}, pages = {1039-1045}, abstract = {Arterial spin labeling (ASL) using magnetic resonance imaging (MRI) is a powerful noninvasive technique to investigate the physiological status of brain tissue by measuring cerebral blood flow (CBF). ASL assesses the inflow of magnetically labeled arterial blood into an imaging voxel. In the last 2 decades, various ASL sequences have been proposed which differ in their ease of implementation and their sensitivity to artifacts. In addition, several quantification methods have been developed to determine the absolute value of CBF from ASL magnetization difference images. In this study, we evaluated three pulsed ASL sequences and three absolute quantification schemes. It was found that FAIR-QUIPSSII implementation of ASL yields 10–20\% higher signal-to-noise ratio (SNR) and 18\% higher CBF as compared with PICORE-Q2TIPS (with FOCI pulses) and PICORE-QUIPSSII (with BASSI pulses). In addition, quantification schemes employed can give rise to up to a 35\% difference in CBF values. We conclude that, although all quant itative ASL sequences and CBF calibration methods should in principle result in the similar CBF values and image quality, substantial differences in CBF values and SNR were found. Thus, comparing studies using different ASL sequences and analysis algorithms is likely to result in erroneous intra- and intergroup differences. Therefore, (i) the same quantification schemes should consistently be used, and (ii) quantification using local tissue proton density should yield the most accurate CBF values because, although still requiring definitive demonstration in future studies, the proton density of blood is assumed to be very similar to the value of gray matter.}, department = {Department MRZ}, web_url = {http://www.sciencedirect.com/science?_ob=PdfDownloadURL\&_uoikey=B6T9D-4WK4B0Y-1\&_tockey=\%23toc\%235112\%239999\%23999999999\%2399999\%23FLA\%23\&_orig=search\&_acct=C000003178\&_version=1\&_userid=29041\&md5=13320c9280bc9acec40024e4b0368f}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, language = {en}, DOI = {10.1016/j.mri.2009.04.002}, author = {Cavusoglu, M and Pfeuffer, J and Ugurbil, K and Uludag, K} } @Article { 5883, title = {Neural activity-induced modulation of BOLD poststimulus undershoot independent of the positive signal}, journal = {Magnetic Resonance Imaging}, year = {2009}, month = {10}, volume = {27}, number = {8}, pages = {1030-1038}, abstract = {Despite intense research on the blood oxygenation level-dependent (BOLD) signal underlying fMRI, our understanding of its physiological basis is far from complete. In this study, it was investigated whether the so-called post-stimulus BOLD signal undershoot is solely a passive vascular effect or actively induced by neural responses. Prolonged static and flickering black-white checkerboard stimulation with isoluminant grey screen as baseline condition were employed on eight human subjects. Within the same region of interest, the positive BOLD time courses for static and flickering stimuli were identical over the entire stimulus duration. In contrast, the static stimuli exhibited no post-stimulus BOLD signal undershoot whereas the flickering stimuli caused a strong BOLD post-stimulus undershoot. To ease the interpretation, we performed an additional study measuring both BOLD signal and cerebral blood flow (CBF) using arterial spin labeling (ASL). Also for CBF a difference in the post-stimulus period was found f or the two stimuli. Thus, a passive blood volume effect as the only contributor to the post-stimulus undershoot comes short in explaining the BOLD post-stimulus undershoot phenomenon for this particular experiment. Rather, an additional active neuronal activation or deactivation can strongly modulate the BOLD post-stimulus behavior. In summary, the post-stimulus time course of BOLD signal could potentially be used to differentiate neuronal activity patterns that are otherwise indistinguishable using the positive evoked response.}, department = {Department MRZ}, web_url = {http://www.sciencedirect.com/science?_ob=MImg\&_imagekey=B6T9D-4X7GBM1-5-C\&_cdi=5112\&_user=29041\&_orig=search\&_coverDate=10\%2F31\%2F2009\&_sk=999729991\&view=c\&wchp=dGLbVtb-zSkWb\&md5=122a16920142222dff87f91960bb0ccf\&ie=}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, language = {en}, DOI = {10.1016/j.mri.2009.04.003}, author = {Sadaghiani, S and Ugurbil, K and Uludag, K} } @Article { 5688, title = {Latin American Brain Mapping Network (LABMAN)}, journal = {NeuroImage}, year = {2009}, month = {8}, volume = {47}, number = {1}, pages = {312-313}, department = {Department MRZ}, web_url = {http://www.sciencedirect.com/science?_ob=MImg\&_imagekey=B6WNP-4VXB8VW-3-1\&_cdi=6968\&_user=29041\&_orig=search\&_coverDate=08\%2F01\%2F2009\&_sk=999529998\&view=c\&wchp=dGLbVlb-zSkWA\&md5=7581b72832a5af4d06ebdaf80c4874e0\&ie=/sdarticle.pdf}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, language = {en}, DOI = {10.1016/j.neuroimage.2009.03.030}, author = {Uludag, K and Evans, A and Della-Maggiore, V and Kochen, S and Amaro, E and Sierra, O and Valdes-Hernandez, P and Medina, V and Valdes-Sosa, P} } @Article { 4956, title = {The Influence of Moderate Hypercapnia on Neural Activity in the Anesthetized Nonhuman Primate}, journal = {Cerebral Cortex}, year = {2008}, month = {11}, volume = {18}, number = {11}, pages = {2666-2673}, abstract = {Hypercapnia is often used as vasodilatory challenge in clinical applications and basic research. In functional magnetic resonance imaging (fMRI), elevated CO2 is applied to derive stimulus-induced changes in the cerebral rate of oxygen consumption (CMRO2) by measuring cerebral blood flow (CBF) and bloodoxygenation- level-dependent (BOLD) signal. Such methods, however, assume that hypercapnia has no direct effect on CMRO2. In this study, we used combined intracortical recordings and fMRI in the visual cortex of anesthetized macaque monkeys to show that spontaneous neuronal activity is in fact significantly reduced by moderate hypercapnia. As expected, measurement of cerebral blood volume using an exogenous contrast agent and of BOLD signal showed that both are increased during hypercapnia. In contrast to this, spontaneous fluctuations of local field potentials in the beta and gamma frequency range as well as multi-unit activity are reduced by \verb=~=15\% during inhalation of 6\% CO2 (pCO2 = 56 mmHg). A strong tendency toward a reduction of neuronal activity was also found at CO2 inhalation of 3\% (pCO2 = 45 mmHg). This suggests that CMRO2 might be reduced during hypercapnia and caution must be exercised when hypercapnia is applied to calibrate the BOLD signal.}, department = {Department Logothetis}, department2 = {Department MRZ}, web_url = {http://cercor.oxfordjournals.org/cgi/reprint/bhn023v2}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, language = {en}, DOI = {10.1093/cercor/bhn023}, author = {Zappe, A-C and Uludag, K and Oeltermann, A and Ugurbil, K and Logothetis, NK} } @Article { 6251, title = {Latin American Brain Mapping Network}, journal = {International Journal of Bioelectromagnetism}, year = {2008}, month = {10}, volume = {10}, number = {4}, pages = {281-299}, abstract = {On March 7-8, 2008, cognitive and imaging neuroscientists from the Americas held a workshop in Havana, Cuba, to launch the Latin American Brain Mapping Network (LABMAN); a project allied to the International Organization for Human Brain Mapping established in 1993. The LABMAN initiative is intended to formalize disparate collaborative threads into a Latin American network via exchange of software, data, personnel, training and ideas through a coordinated network, both organizational and electronic. In general, neuroscience and neuroimaging research in Latin America is hindered by a lack of critical mass within any single country. By organizing these communities at a supra-national level, LABMAN seeks to nurture brain mapping research at the national level, acting as a catalyst for national programs. Furthermore, in this report, statuses of brain mapping in different Latin American countries (Argentina, Brazil, Columbia, Cuba and Mexico) are summarized. This is not meant to be an exhaustive report about neuroimaging work in these countries but rather to underscore the potential of the region in the development and use of brain mapping as a research and health tool. We are inviting research groups and individuals in Latin America not represented currently to join LABMAN.}, department = {Department MRZ}, web_url = {http://ijbem.k.hosei.ac.jp/volume10/number4/100407.pdf}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, language = {en}, author = {Uludag, K and Evans, AC and Della-Maggiore, V and Murer, G and Amaro, E and Sierra, O and Valdes-Hernandez, P and Medina, V and Valdes-Sosa, P} } @Article { 5690, title = {Decreases in ADC observed in tissue areas during activation in the cat visual cortex at 9.4 T using high diffusion sensitization}, journal = {Magnetic Resonance Imaging}, year = {2008}, month = {9}, volume = {26}, number = {7}, pages = {889-896}, department = {Department MRZ}, web_url = {http://www.sciencedirect.com/science?_ob=MImg\&_imagekey=B6T9D-4SHN0FD-1-C\&_cdi=5112\&_user=29041\&_orig=browse\&_coverDate=09\%2F30\%2F2008\&_sk=999739992\&view=c\&wchp=dGLbVlb-zSkWb\&md5=e92eddd8aa2f8f55c94cfdbb43a80176\&ie=/sdarticle.pdf}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, language = {en}, DOI = {10.1016/j.mri.2008.01.046}, author = {Yacoub, E and Uludag, K and Harel, N} } @Article { 4918, title = {Direct measurement of oxygen extraction with fMRI using 6\% CO2 inhalation}, journal = {Magnetic Resonance Imaging}, year = {2008}, month = {9}, volume = {26}, number = {7}, pages = {961-967}, abstract = {The blood oxygenation level-dependent (BOLD) signal is an indirect hemodynamic signal which is sensitive to cerebral blood flow (CBF), cerebral blood volume (CBV) and cerebral metabolic rate of oxygen (CMRO2). Therefore, the BOLD signal amplitude and dynamics cannot be interpreted unambiguously without additional physiological measurements and, thus, there remains a need for a functional magnetic resonance imaging (fMRI) signal which is more closely related to the underlying neuronal activity. In this study, we measured cerebral blood flow with continuous arterial spin labeling, cerebral blood volume with an exogenous contrast agent and BOLD combined with intracortical electrophysiological recording in primary visual cortex of the anesthetized monkey. During inhalation of 6\% CO2, it was observed that CBF and CBV are not further increased by a visual stimulus, although baseline CBF for 6\% CO2 is below the maximal value of CBF. In contrast, the electrophysiological response to the stimulation was found to be preserved during hypercapnia. As a consequence, the simultaneously measured BOLD signal responds negatively to a visual stimulation for 6\% CO2 inhalation in the same voxels responding positively during normocapnia. These observations suggest that the fMRI response to a sensory stimulus for 6\% CO2 inhalation occurs in the absence of a hemodynamic response, and it therefore directly reflects the oxygen extraction into the tissue.}, department = {Department Logothetis}, department2 = {Department MRZ}, web_url = {http://www.sciencedirect.com/science?_ob=MImg\&_imagekey=B6T9D-4SDNK82-1-1\&_cdi=5112\&_user=29041\&_orig=search\&_coverDate=09\%2F30\%2F2008\&_sk=999739992\&view=c\&wchp=dGLzVtb-zSkzS\&md5=a68ebcb9c19df1431bbf6ced51eeb30a\&ie=/sdarticle.pdf}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, language = {en}, DOI = {10.1016/j.mri.2008.02.005}, author = {Zappe, A-C and Uludag, K and Logothetis, NK} } @Article { 4930, title = {Dynamics and nonlinearities of the BOLD response at very short stimulus durations}, journal = {Magnetic Resonance Imaging}, year = {2008}, month = {9}, volume = {26}, number = {7}, pages = {853-862}, url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/Yesilyurt_short_4930[0].pdf}, department = {Department MRZ}, web_url = {http://www.sciencedirect.com/science?_ob=MImg\&_imagekey=B6T9D-4SH1HXR-4-3\&_cdi=5112\&_user=29041\&_orig=search\&_coverDate=09\%2F30\%2F2008\&_sk=999739992\&view=c\&wchp=dGLbVlb-zSkzS\&md5=b924b591649b952b977639014a1c192a\&ie=/sdarticle.pdf}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, language = {en}, DOI = {10.1016/j.mri.2008.01.008}, author = {Yesilyurt, B and Ugurbil, K and Uludag, K} } @Article { 5175, title = {Transient and sustained BOLD responses to sustained visual stimulation}, journal = {Magnetic Resonance Imaging}, year = {2008}, month = {9}, volume = {26}, number = {7}, pages = {863-869}, abstract = {Examining the transients of the blood-oxygenation-level-dependent (BOLD) signal using functional magnetic resonance imaging is a tool to probe basic brain physiology. In addition to the so-called initial dip and poststimulus undershoot of the BOLD signal, occasionally, overshoot at the beginning and at the end of stimulation and stimulus onset and offset (‘phasic’) responses are observed. Hemifield visual stimulation was used in human subjects to study the latter transients. As expected, sustained (‘tonic’) stimulus-correlated contralateral activation in the visual cortex and LGN was observed. Interestingly, bilateral phasic responses were observed, which only partly overlapped with the tonic network and which would have been missed using a standard analysis. A biomechanical model of the BOLD signal (‘balloon model’) indicated that, in addition to phasic neuronal activity, vascular uncoupling can also give rise to phasic BOLD signals. Thus, additional physiological information (i.e., cerebral blood flow ) and examination of spatial distribution of the activity might help to assess the BOLD signal transients correctly. In the current study, although vascular uncoupled responses cannot be ruled out as an explanation of the observed phasic BOLD network, the spatial distribution argues that sustained hemifield visual stimulation evokes both bilateral phasic and contralateral sustained neuronal responses. As a consequence, in rapid event-related experimental designs, both the phasic and tonic networks cannot be separated, possibly confounding the interpretation of BOLD signal data. Furthermore, a combination of phasic and tonic responses in the same region of interest might also mimic a BOLD response typically observed in adaptation experiments.}, department = {Department MRZ}, web_url = {http://www.sciencedirect.com/science?_ob=MImg\&_imagekey=B6T9D-4SH1HXR-2-7\&_cdi=5112\&_user=29041\&_orig=search\&_coverDate=09\%2F30\%2F2008\&_sk=999739992\&view=c\&wchp=dGLzVlz-zSkzV\&md5=80dbe3007ee6d02c805bb23ff932f62b\&ie=/sdarticle.pdf}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, language = {en}, DOI = {10.1016/j.mri.2008.01.049}, author = {Uludag, K} } @Article { 5386, title = {Simultaneous PET-MRI: a new approach for functional and morphological imaging}, journal = {Nature Medicine}, year = {2008}, month = {4}, volume = {14}, number = {4}, pages = {459-465}, abstract = {Noninvasive imaging at the molecular level is an emerging field in biomedical research. This paper introduces a new technology synergizing two leading imaging methodologies: positron emission tomography (PET) and magnetic resonance imaging (MRI). Although the value of PET lies in its high-sensitivity tracking of biomarkers in vivo, it lacks resolving morphology. MRI has lower sensitivity, but produces high soft-tissue contrast and provides spectroscopic information and functional MRI (fMRI). We have developed a three-dimensional animal PET scanner that is built into a 7-T MRI. Our evaluations show that both modalities preserve their functionality, even when operated isochronously. With this combined imaging system, we simultaneously acquired functional and morphological PET-MRI data from living mice. PET-MRI provides a powerful tool for studying biology and pathology in preclinical research and has great potential for clinical applications. Combining fMRI and spectroscopy with PET paves the way for a new perspective in molecular imaging.}, department = {Department MRZ}, web_url = {http://www.nature.com/nm/journal/v14/n4/pdf/nm1700.pdf}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, language = {en}, DOI = {10.1038/nm1700}, author = {Judenhofer, MS and Wehrl, HF and Newport, DF and Catana, C and Siegel, SB and Becker, M and Thielscher, A and Kneilling, M and Lichy, MP and Eichner, M and Klingel, K and Reischl, G and Widmaier, S and R{\"o}cken, M and Nutt, RE and Machulla, H-J and Uludag, K and Cherry, SR and Claussen, CD and Pichler, BJ} } @Article { 4817, title = {Magnetic Field Distribution and Signal Decay in Functional MRI in Very High Fields (up to 9.4 T) Using Monte-Carlo Diffusion Modeling}, journal = {International Journal of Biomedical Imaging}, year = {2007}, month = {8}, volume = {2007}, number = {70309}, pages = {1-7}, department = {Department MRZ}, web_url = {http://www.hindawi.com/GetPDF.aspx?doi=10.1155/2007/70309}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, language = {en}, DOI = {10.1155/2007/70309}, author = {M{\"u}ller-Bierl, BM and Uludag, K and Pereira, P and Schick, F} } @Article { 5691, title = {Relevance of depth resolution for cerebral blood flow monitoring by near-infrared spectroscopic bolus tracking during cardiopulmonary bypass}, journal = {Journal of Thoracic and Cardiovascular Surgery}, year = {2006}, month = {11}, volume = {132}, number = {5}, pages = {1172-1178}, abstract = {Objective Noninvasive near-infrared spectroscopy (NIRS) is increasingly used to monitor cerebral oxygenation and blood flow status, which is also of high relevance during cardiovascular surgical interventions with cardiopulmonary bypass. Contamination of the cerebral signal by contamination from overlaying extracerebral tissue, however, has been proposed to reduce sensitivity and cerebral selectivity of this promising technique. Methods We evaluated a novel depth-resolved approach for the determination of cerebral hemodynamics by near-infrared spectroscopic tracking of intravenously administered indocyanine green boluses. A frequency domain technique was applied, allowing simultaneous determination of light absorption changes and time of flight of single photons and enabling the differentiation between extracerebral and intracerebral tracer kinetics. Depth-resolved near-infrared spectroscopy was tested in 4 patients undergoing cardiopulmonary bypass and compared with data derived by conventional continuous-wave near-infrared spectroscopy. Results Depth resolution extracted the differential responses of extracerebral and intracerebral blood vessels from near-infrared bolus tracking signals. Postoperative blood flow indices derived from the intracerebral time course exceeded preoperative values by 1.5 ± 0.2 times, indicating a significant increase of cerebral blood flow not detectable by conventional near-infrared spectroscopy. Conclusion The depth-resolved approach provides additional and relevant data for the interpretation of intraoperative cerebral perfusion during cardiothoracic surgery. The validity of this approach for patients with preexisting risk factors for cerebral hypoperfusion remains to be determined in larger clinical trials.}, web_url = {http://www.sciencedirect.com/science?_ob=MImg\&_imagekey=B6WMF-4M5F25X-16-1\&_cdi=6933\&_user=29041\&_orig=browse\&_coverDate=11\%2F30\%2F2006\&_sk=998679994\&view=c\&wchp=dGLbVlz-zSkzV\&md5=1d14bc4950fbafaa8348c44999f060d4\&ie=/sdarticle.pdf}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, language = {en}, DOI = {10.1016/j.jtcvs.2006.05.065}, author = {Steinbrink, J and Fischer, T and Kuppe, H and Hetzer, R and Uludag, K and Obrig, H and Kuebler, WM} } @Article { 4075, title = {Frontiers of Brain Mapping using MRI}, journal = {Journal of Magnetic Resonance Imaging}, year = {2006}, month = {6}, volume = {23}, number = {6}, pages = {945-957}, abstract = {Over the past dozen years, the use of MRI techniques to map brain function (fMRI) has sparked a great deal of research. The ability of fMRI to image several different physiological processes concurrently (i.e., blood oxygenation, blood flow, metabolism) and noninvasively over large volumes make it the ideal choice for many different areas of neuroscience research in addition to countless applications in clinical settings. Furthermore, with the advent of high magnetic fields (and other hardware advancements, i.e., parallel imaging) for both human and animal research, spatial and temporal resolutions continue to be pushed to higher levels because of increases in the sensitivity as well as specificity of MR-detectable functional signals. fMRI methodology continues to grow and has the ability to cater to many different research applications. There seems to be no foreseeable end in sight to the advancement of fMRI techniques and its subsequent use in basic research as well as in clinical settings. In this work, fMRI techniques and the ongoing development of existing techniques are discussed with implications for the future of fMRI.}, department = {Department MRZ}, web_url = {http://www3.interscience.wiley.com/cgi-bin/fulltext/112599305/PDFSTART}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, language = {en}, DOI = {10.1002/jmri.20576}, author = {Harel, N and Ugurbil, K and Uludag, K and Yacoub, E} } @Article { 5692, title = {Investigating the post-stimulus undershoot of the BOLD signal—a simultaneous fMRI and fNIRS study}, journal = {NeuroImage}, year = {2006}, month = {4}, volume = {30}, number = {2}, pages = {349-358}, abstract = {Measuring the hemodynamic response with functional magnetic resonance imaging (fMRI) together with functional near-infrared spectroscopy (fNIRS) may overcome limitations of single-method approaches. Accordingly, we measured the event-related hemodynamic response with both imaging methods simultaneously in young subjects during visual stimulation. An intertrial interval of 60 s was chosen to include the prolonged post-stimulus undershoot of the blood oxygenation level dependent (BOLD) signal. During visual stimulation, the BOLD signal, oxy-, and total hemoglobin (Hb) increased, whereas deoxy-Hb decreased. The post-stimulus period was characterized by an undershoot of the BOLD signal, oxy-Hb, and an overshoot of deoxy-Hb. Total Hb as measured by fNIRS returned to baseline immediately after the end of stimulation. Results suggest that the post-stimulus events as measured by fNIRS are dominated by a prolonged high-level oxygen consumption in the microvasculature. The contribution of a delayed return of blood volume to the BOLD post-stimulus undershoot in post-capillary veins as suggested by the Balloon and Windkessel models remains ambiguous. Temporal changes in the BOLD signal were highly correlated with deoxy-Hb, with lower correlation values for oxy- and total Hb. Furthermore, data show that fNIRS covers the outer 1 cm of the brain cortex. These results were confirmed by simultaneous fMRI/fNIRS measurements during rest. In conclusion, multimodal imaging approaches may contribute to the understanding of neurovascular coupling.}, web_url = {http://www.sciencedirect.com/science?_ob=MImg\&_imagekey=B6WNP-4HDX6TS-4-5\&_cdi=6968\&_user=29041\&_orig=browse\&_coverDate=04\%2F01\%2F2006\&_sk=999699997\&view=c\&wchp=dGLbVlz-zSkWb\&md5=739f2451cad3e79e2c2cd91d770ebb48\&ie=/sdarticle.pdf}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, language = {en}, DOI = {10.1016/j.neuroimage.2005.09.048}, author = {Schroeter, ML and Kupka, T and Mildner, T and Uludag, K and von Cramon, DY} } @Article { SchroeterBMUOLTVv2004, title = {Towards a standard analysis for functional near-infrared imaging}, journal = {NeuroImage}, year = {2004}, month = {1}, volume = {21}, number = {1}, pages = {283–290}, abstract = {Functional near-infrared spectroscopy (fNIRS) allows the ability to monitor brain activation by measuring changes in the concentration of oxy- and deoxy-hemoglobin. Until now no standardized approach for fNIRS data analysis has been established, although this has to be regarded as a precondition for future application. Hence, we applied the well-established general linear model to optical imaging data. Further, fNIRS data were analyzed in the frequency domain. Two visual tasks were investigated with optical imaging: a checkerboard paradigm supposed to activate the primary and secondary visual cortex, and a paradigm consisting of moving colored stimuli (rotating ‘L’s) additionally involving the motion area V5. Analysis with the general linear model detected the activation focus in the primary and secondary visual cortex during the first paradigm. For the second paradigm, a second laterally localized activated brain region was found, most likely representing V5. Spatially resolved spectral analysis confirmed the results by showing maxima of power spectral density and coherence in the same respective brain regions. Moreover, it demonstrated a delay of the hemodynamic response in the motion area. In summary, the present study suggests that the general linear model and spatially resolved spectral analysis can be used as standard statistical approaches for optical imaging data, particularly because they are almost independent of the assumed differential path length factors.}, web_url = {http://www.sciencedirect.com/science/article/pii/S1053811903006049}, DOI = {10.1016/j.neuroimage.2003.09.054}, author = {Schroeter, ML and B{\"u}cheler, MM and M{\"u}ller, K and Uludag, K and Obrig, H and Lohmann, G and Tittgemeyer, M and Villringer, A and von Cramon, DY} } @Poster { CavusogluBU2012, title = {Retinotopic maps and hemodynamic delays in the human visual cortex measured using arterial spin labeling}, year = {2012}, month = {5}, volume = {20}, number = {578}, department = {Department Scheffler}, department2 = {Department Logothetis}, web_url = {http://www.ismrm.org/12/Session57.htm}, event_place = {Melbourne, Australia}, event_name = {20th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2012)}, author = {Cavusoglu, M and Bartels, A and Uludag, K} } @Poster { 7091, title = {Measurement of CMRO2 changes by somatosensory stimulation in rat using oxygen-17 at 16.4 T}, year = {2011}, month = {5}, volume = {19}, number = {5868}, abstract = {We have observed the first directly measured CMRO2 changes in rats by peripheral somatosensory stimulation at an ultrahigh field strength of 16.4 Tesla. The results show that apart from the high sensitivity required also the stability of baseline metabolism is crucial in detecting small CMRO2 changes evoked by increased neural activity. Lower global baseline metabolism was found when ventilating with a N2O vs. N2 mixture of equal O2 fraction due to the increased anesthetic effect of N2O in agreement with previous work. The direct detection of changes in CMRO2 can also help to investigate the metabolic changes in negative BOLD activations on the ipsilateral hemisphere. Our results are also in accordance with previous results using 17O for CMRO2 measurements from other species at 9.4T.}, url = {http://www.kyb.tuebingen.mpg.defileadmin/user_upload/files/publications/2011/ISMRM-2011-Wiesner.pdf}, department = {Department MRZ}, department2 = {Department Scheffler}, web_url = {http://www.ismrm.org/11/}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, event_place = {Montr{\'e}al, Canada}, event_name = {19th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2011)}, language = {en}, digital = {1}, author = {Wiesner, HM and Pohmann, R and Balla, DZ and Chen, W and Ugurbil, K and Uludag, K} } @Poster { MullerBierlPKUU2012, title = {A realistic vascular model for BOLD signal up to 16.4 T}, year = {2010}, month = {5}, volume = {2010}, number = {1129}, abstract = {The blood oxygenation level-dependent (BOLD) signal using functional magnetic resonance imaging (fMRI) is currently the most popular imaging method to study brain function non-invasively. The sensitivity of the BOLD signal to different types of MRI sequences and vessel sizes is currently under investigation [1]. Gradient echo (GRE) sequences are known to be sensitive to larger vessels (venules and veins), whereas spin-echo (SE) sequences are generally more sensitive to smaller vessels (venules and capillaries), especially at high magnetic field strength [2, 3]. However, the widely used single vessel model is only an approximation to the realistic vascular distribution. Realistic vascular models have been proposed by Marques and Bowtell [4] and, recently, by Chen et al.[5]. We herein present a realistic vascular model (RVM) where diffusion is accounted for by a Monte-Carlo random walk.}, url = {http://www.kyb.tuebingen.mpg.defileadmin/user_upload/files/publications/ISMRM-2010-1129.PDF}, department = {Department MRZ}, department2 = {Research Group Kerr}, web_url = {http://www.ismrm.org/10/}, event_place = {Stockholm, Sweden}, event_name = {ISMRM-ESMRMB Joint Annual Meeting 2010}, author = {M{\"u}ller-Bierl, AM and Pawlak, V and Kerr, J and Ugurbil, K and Uludag, K} } @Poster { 5940, title = {Dynamics of positive and negative BOLD responses in visual cortex}, journal = {NeuroImage}, year = {2009}, month = {7}, volume = {47}, number = {Supplement 1}, pages = {S154}, abstract = {Introduction Previous studies have shown that besides the commonly observed positive BOLD response (PBR), a negative BOLD response (NBR) also exists [1] which was suggested to reflect decreased neuronal activity [2] and oxygenation [3]. However, the underlying physiology of NBR is still not clear and the dynamics of NBR has not been yet extensively explored. Our aim in this study was to investigate the dynamics of NBR and compare these with the dyamics of PBR. To this end, we used two different visual stimulus designs in which the baseline conditions were the same. During stimulation, however, the luminance level was either increased or decreased. We showed that mirroring the stimulus design does not simply mirrors the BOLD response and that the dynamics of NBR differs from PBR. Methods fMRI data were collected at 3T Siemens Tim-Trio scanner using GRE-EPI sequence (TR/TE=1000/35ms, voxel-size=3.1\(\times\)3.1\(\times\)3.5mm). Full field, black-white checkerboard stimuli rotating at 8Hz were presented to subjects (10 subjects) with four different Michelson contrast level (100\%, 75\%, 25\%, 12.5\%, gamma corrected) whereas the baseline condition was set to 50\% contrast (40s baseline, 5s stimulus; 12 trials). On functional activation maps, 100 most activated voxels in the visual cortex were chosen and time courses of these voxels averaged among trials. Time courses were resampled at 0.1s using data interpolation. Standard deviation (STD) of baseline was calculated for the time points −5 to 0. Time-to-onset of BOLD response was defined as the time point deviating 2 STD from the baseline mean value. Results Positive contrast stimuli (100\%, 75\%) elicited positive activation in the early visual areas (red in Fig.1), whereas negative contrast stimuli (25\%, 12.5\%) evoked negative (green in Fig.1) as well as positive activation (blue in Fig.1) in posterior and anterior part of the visual cortex, respectively. Average time courses in negative activation region as well as in lateral geniculate nucleus (LGN) are depicted in figure 2-3. Time-to-onset values of negative contrast responses were not significantly different from positive contrast responses (p>0.05), whereas in time-to-peak values negative contrast responses slightly preceded their positive counterparts (Table 1). Although, the absolute peak amplitudes of responses were similar (p>0.05), their widths were not (p<0.05): 0.62\% and 0.65\% BOLD signal for 25\% and 75\%, 6.2s and 4.6s for 25\% and 75\%, respectively. Conclusions Our results show that under the same baseline condition, the negative BOLD response is not simply the inverse of its positive counterpart. Dynamics of the former differs significantly from the latter. Negative responses peak earlier and their FWHM is shorter. Additionally, functional activation maps to positive and negative contrast stimuli show discrepancies; whereas positive contrast evoke only positive response, negative contrast evokes both positive and negative responses in distinct regions of visual cortex. In response to decreasing contrast, BOLD response in LGN decreases as well (Fig. 3), however, response characteristics in LGN are different compared to visual cortex. In conclusion, similar time-to-onset values of negative and positive BOLD responses can be a sign of identical initial underlying mechanisms, and hence, can be well explained by a feed-forward neurovascular coupling.}, url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/HBM_2009_POSTER_Yesilyurt_Baris_5940[0].pdf}, department = {Department MRZ}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, event_place = {San Francisco, CA, USA}, event_name = {15th Annual Meeting of the Organisation for Human Brain Mapping (HBM 2009)}, language = {en}, DOI = {10.1016/S1053-8119(09)71602-7}, author = {Yesilyurt, B and Uludag, K} } @Poster { 6051, title = {Interleaved TMS/CASL: Comparison of different rTMS protocols}, journal = {NeuroImage}, year = {2009}, month = {7}, volume = {47}, number = {Supplement 1}, pages = {S170}, department = {Department MRZ}, web_url = {http://www.sciencedirect.com/science?_ob=MImg\&_imagekey=B6WNP-4X3PHYG-29K-1\&_cdi=6968\&_user=29041\&_pii=S1053811909718373\&_orig=search\&_coverDate=07\%2F31\%2F2009\&_sk=999529999.8998\&view=c\&wchp=dGLzVzz-zSkWz\&md5=6840d2d050057afd95d23fcd95b1e3c9\&ie=/sdarticle}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, language = {en}, DOI = {10.1016/S1053-8119(09)71837-3}, author = {Moisa, M and Uludag, K and Pohmann, R and Thielscher, A} } @Poster { 5742, title = {17 O T1/T2* tissue-relaxation rates with anatomical contrast in the rat brain at 16.4 T}, year = {2009}, month = {4}, volume = {17}, number = {354}, abstract = {The direct NMR detection of 17O benefits particularly from higher field strengths and is a promising tool in the study of cerebral oxygen metabolism. The aim of this study was to acquire anatomical MRS images of H2O17 at natural abundance concentration in the rat head at 16.4 T. Intra-cortical contrast and differences in tissue-specific relaxation of brain and muscle tissue were found, enabling optimizations in contrast and sensitivity. Based on these results implications on the spatial specificity of oxygen consumption (CMRO2) measurements using 17O2-enriched gas are discussed.}, url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/Abstract1544_17ORelaxationRatesAndContrast_5742[0].pdf}, department = {Department MRZ}, web_url = {http://www.ismrm.org/09/}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, institution = {Max Planck Institute for Biological Cybernetics, T{\"u}bingen, Germany}, event_place = {Honolulu, HI, USA}, event_name = {17th Annual Meeting of the International Society for Magnetic Resonance in Medicine (ISMRM 2009)}, language = {en}, author = {Wiesner, HM and Balla, DZ and Pohmann, R and Chen, W and Ugurbil, K and Uludag, K} } @Poster { UludagZGL2009, title = {Calibrating the BOLD signal revisited – Calculation of oxygen metabolism for gradient- and spin-echo sequence up to 16.4T}, year = {2009}, month = {4}, volume = {17}, number = {3701}, abstract = {A BOLD signal model as a function oxygen extraction fraction and CBV was developed in order to determine change in oxidative metabolism from combined BOLD signal and CBF measurements. The new model is an alternative model to the widely used calibrated BOLD approach initally proposed by Davis and colleagues for GRE at 1.5T. The new model, however, takes also intra-vascular MRI signal into account and is developed for both GRE and SE from 1.5T up to 16.4T. In the current study, at 4.7T and 7T using SE and GRE, oxidative metabolism change during visual stimulation was determined in macaque monkeys.}, url = {http://www.kyb.tuebingen.mpg.defileadmin/user_upload/files/publications/ISMRM-2009-03701.pdf}, department = {Department Logothetis}, web_url = {http://www.ismrm.org/09/}, event_place = {Honolulu, HI, USA}, event_name = {17th Annual Meeting of the International Society for Magnetic Resonance in Medicine (ISMRM 2009)}, author = {Uludag, K and Zappe, A-C and Goense, J and Logothetis, NK} } @Poster { 5698, title = {In-vivo T1 and T2* tissue-relaxation rates of H2O17 at 16.4 Tesla}, year = {2008}, month = {10}, day = {15}, volume = {2008}, abstract = {The measurement of cerebral metabolic rate of oxygen (CMRO2) via direct NMR detection of the stable oxygen isotope 17O is a promising tool to study alterations in brain activity and pathology. Due to the low natural abundance of 0.037\% H2O17, optimized acquisition parameters are crucial for 17O-weigthed MRI of metabolically produced cerebral water. It has been suggested that signal-to-noise ratio increases almost quadratically with B0 due to field-independent quadrupolar interactions of 17O. Thus, in comparison to studies at lower field strengths the increased magnetization available at 16.4 T allows an enhanced spatial resolution and thus for the first time a tissue-specific determination of 17O relaxation.}, url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/ISMRM2008-Workshop-Rome-Wiesner_[0].pdf}, department = {Department MRZ}, web_url = {http://www.ismrm.org/workshops/HF2008/index.htm}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, event_place = {Toronto, Canada}, event_name = {ISMRM Workshop on High-Field Systems and Applications 2008: ''Whats special about 7T+?''}, language = {en}, digital = {1}, author = {Wiesner, HM and Balla, DZ and Pohmann, R and Chen, W and Ugurbil, K and Uludag, K} } @Poster { 5319, title = {Interleaved TMS/CASL: A motor cortex study}, journal = {Brain Stimulation}, year = {2008}, month = {7}, volume = {1}, number = {3}, pages = {290-291}, abstract = {CASL (continuous arterial spin labeling) offers the possibility of measuring simultaneously rCBF (regional cerebral blood flow) as well as the BOLD effect. The aim of this study is to demonstrate the technical feasibility to combine TMS with multi slice CASL imaging.}, department = {Department MRZ}, web_url = {http://www.sciencedirect.com/science?_ob=PdfDownloadURL\&_uoikey=B8JBG-4T8JVVB-5C\&_tockey=\%23toc\%2343558\%232008\%23999989996\%23696438\%23FLA\%23\&_orig=search\&_acct=C000003178\&_version=1\&_userid=29041\&md5=fd0631b85d11cc4c84e26de4420ab78c}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, language = {en}, DOI = {10.1016/j.brs.2008.06.136}, author = {Moisa, M and Pohmann, R and Uludag, K and Thielscher, A} } @Poster { 4935, title = {BOLD Response in Lateral Geniculate Nucleus (LGN) at Very Short Stimulus Durations}, journal = {NeuroImage}, year = {2008}, month = {6}, volume = {41}, number = {Supplement 1}, pages = {S94}, abstract = {Lateral geniculate nucleus is a small-sized structure located in thalamus and targeted by predominant fraction of the retinal ganglion cells. That is, LGN, besides other cortical sub-cortical areas, is involved in the processing of visual information. Thus, previous fMRI studies successfully mapped activation in LGN despite its small size and quite poor BOLD response. In addition, we have recently shown a BOLD response to visual stimulation as short as 5ms in visual cortex. Our aim in this study was to characterize the BOLD response in the LGN at comparable short stimulus durations. Our findings were; a) with an appropriate design and adequate averaging a BOLD response to 10ms stimulus can be revealed in LGN b) BOLD responses in LGN exhibit non-linear behavior similar to that in visual cortex}, url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/SPLTRAK\%20Abstract\%20Submission_[0].pdf}, department = {Department MRZ}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, event_place = {Melbourne, Australia}, event_name = {14th Annual Meeting of the Organization for Human Brain Mapping (HBM 2008)}, language = {en}, DOI = {10.1016/j.neuroimage.2008.04.008}, author = {Yesilyurt, B and Ugurbil, K and Uludag, K} } @Poster { 5686, title = {Comparison of Pulsed Arterial Spin Labeling Sequences Using Different Absolute Quantification Methods}, year = {2008}, month = {5}, volume = {16}, number = {1930}, pages = {324}, abstract = {Three different ASL schemes (Q2TIPS, FAIR-QUIPSSII and PICORE-QUIPSSII with asymmetric BASSI pulses) were compared measuring absolute cerebral blood flow (CBF) in the human brain at 3T. Signal-to-noise ratios (SNR), magnetization difference between control and tag images and three different absolute CBF quantification schemes were evaluated. For identical sequence parameters and voxels, it was found that a) FAIR-QUIPSSII has the highest SNR b) FAIR-QUIPSSII yields slightly higher CBF values c) absolute CBF values depend on the quantification scheme utilized. One possible explanation for the findings is that effective labeling efficiency and physiological noise contamination are different for the tagging procedures used.}, url = {http://www.kyb.tuebingen.mpg.defileadmin/user_upload/files/publications/ISMRM-2008-01930.pdf}, department = {Department MRZ}, web_url = {http://www.ismrm.org/08/}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, event_place = {Toronto, Canada}, event_name = {16th Scientific Meeting and Exhibition of the International Society of Magnetic Resonance in Medicine (ISMRM 2008)}, language = {en}, author = {Cavusoglu, M and Ugurbil, K and Uludag, K} } @Poster { ZappeUL2008, title = {Negative BOLD Signal Under 6\% Hypercapnia Reflects Solely Oxygen Extraction from the Blood}, year = {2008}, month = {5}, volume = {16}, number = {850}, pages = {166}, abstract = {The BOLD signal is sensitive to cerebral blood flow (CBF), blood volume (CBV) and oxygen extraction. In the anesthetized monkey, we observe a vasodilatory ceiling effect during inhalation of 6\% CO2 where CBF or CBV are not further increased by visual stimulation. In contrast, simultaneously measured local field potential responds to the stimulation as strong as during normocapnia. As a consequence, the stimulus-induced fMRI response during 6\% hypercapnia has been found to be negative reflecting only the oxygen extraction from the blood. With this method, oxygen extraction can be imaged by means of fMRI without injection of an exogenous drug.}, url = {http://www.kyb.tuebingen.mpg.defileadmin/user_upload/files/publications/ISMRM-2008-00850.pdf}, department = {Department Logothetis}, web_url = {http://www.ismrm.org/08/}, event_place = {Toronto, Canada}, event_name = {16th Scientific Meeting and Exhibition of the International Society of Magnetic Resonance in Medicine (ISMRM 2008)}, author = {Zappe, A-C and Uludag, K and Logothetis, NK} } @Poster { 4578, title = {Neural basis of TMS induced suppression during a visual discrimination task}, year = {2007}, month = {7}, volume = {10}, pages = {90}, abstract = {In Transcranial Magnetic Stimulation (TMS), strong magnetic pulses delivered by a coil placed over the subject’s head are used to induce neural activity in a focal area of the brain. TMS can be used to demonstrate a causal relationship between behavior and the neural processing in a brain structure of interest by showing that a subject’s task performance is diminished during TMS stimulation of that structure (i.e., the “virtual lesion” approach [1]). We addressed two questions in the current study: 1) How well does the position of the maximal TMS effect coincide with the brain activation pattern observed during the task using other neuroimaging techniques such as fMRI or PET? 2)Which visual area is most critical for conscious perception of a visual stimulus, i.e. which visual area has to be disturbed after stimulus presentation to diminish the recognition performance significantly? (“visual suppression” effect [2,3]). In all subjects, the spatial pattern of the TMS effect was smooth and the coil positions at which the maximal suppression occurred were located next to each other. This indicates that the TMS target was a single continuous brain structure and not, e.g. two or more separate sub-areas. The Center of Gravity (CoG) of the TMS map was consistently positioned over the inferior part of the superior occipital gyrus. As expected, the fMRI activation pattern was rather extended and covered several visual areas. The TMS CoG was consistently located over the medial-inferior part of the fMRI activation. Visual mapping [4] delineated the TMS CoG being significantly closer to the CoG of V2 than to any other visual area. Mean deviation of TMS CoG from V2 CoG obtained with fMRI was 5.1mm (SE 0.6mm, n=7), showing a good spatial congruence between these two neuroimaging techniques. Several control studies were performed to test for possible involvement of other visual areas. The findings suggest that V2 and not primary visual cortex V1 is the brain area primarily targeted in visual suppression. In consequence, our data does not support the special role of V1 in conscious visual perception as previously suggested by several authors (for review see [5]).}, department = {Department MRZ}, web_url = {http://twk.tuebingen.mpg.de/twk07/abstract.php?_load_id=reichenbach01}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, event_place = {T{\"u}bingen, Germany}, event_name = {10th T{\"u}binger Wahrnehmungskonferenz (TWK 2007)}, language = {en}, author = {Reichenbach, A and Thielscher, A and Ugurbil, K and Uludag, K} } @Poster { 4526, title = {The cortical site of visual suppression by transcranial magnetic stimulation}, journal = {NeuroImage}, year = {2007}, month = {6}, volume = {36}, number = {Supplement 1}, pages = {S86}, department = {Department MRZ}, web_url = {http://www.sciencedirect.com/science/article/pii/S1053811907002789}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, institution = {Organization for Human Brain Mapping}, event_place = {Chicago, IL, USA}, event_name = {13th Annual Meeting of the Organization for Human Brain Mapping (HBM 2007)}, language = {en}, DOI = {10.1016/j.neuroimage.2007.03.045}, author = {Thielscher, A and Reichenbach, A and Ugurbil, K and Uludag, K} } @Poster { 4934, title = {The Dynamics of ERP and Hemodynamic Responses at Very Short Stimulus Durations}, journal = {NeuroImage}, year = {2007}, month = {6}, volume = {36}, number = {Supplement 1}, pages = {S47}, abstract = {Complementary non-invasive imaging methods on human subjects such as EEG and fMRI can provide new insights into the functioning of the brain and into neurovascular coupling. Particularly, short stimulus durations rather than commonly used standard durations in fMRI experiments are suitable to study the relationship between electrophysiological and vascular measures because of reduction of non-linearities of the hemodynamic response [1]. In this study, using very short stimulus durations (0.1 ms to 5 ms) and measurements with fMRI and EEG we have found that both N75 of the visual evoked potentials and BOLD signal increase and P100 decrease with stimulus duration. In addition, the BOLD signal poststimulus undershoot also tends to deviate more with stimulus duration. These results allow to shed light on whether and which ERP components correlate well with the BOLD signal.}, url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/HBM_2007_POSTER_YES_[0].pdf}, department = {Department MRZ}, web_url = {http://www.sciencedirect.com/science/article/pii/S1053811907002789}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, event_place = {Chicago, IL, USA}, event_name = {13th Annual Meeting of the Organization for Human Brain Mapping (HBM 2007)}, language = {en}, DOI = {10.1016/j.neuroimage.2007.03.045}, author = {Yesilyurt, B and Whittingstall, K and Sengupta, B and Ugurbil, K and Uludag, K} } @Poster { 4495, title = {Congruence between BOLD activation pattern and the maximal suppression effect by TMS during a simple visual discrimination task}, year = {2007}, month = {5}, volume = {2007}, number = {2023}, pages = {400}, abstract = {Transcranial Magnetic Stimulation can interfere with the neural processing in a brain area-of-interest. How well the spatial pattern of TMS interference coincides with the activation pattern observed in fMRI was evaluated. The coil position at which TMS suppressed the perception of a visual stimulus was determined and compared with the stimulus-related BOLD activation. The TMS effect consistently occurred over a specific subpart of the fMRI activation. While fMRI is capable of characterizing the general pattern of brain areas activated in a certain task, TMS has the potential to specifically localize those areas being most critical for the task.}, department = {Department MRZ}, web_url = {http://www.ismrm.org/07/}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, event_place = {Berlin, Germany}, event_name = {2007 Joint Annual Meeting ISMRM-ESMRMB}, language = {en}, author = {Thielscher, A and Reichenbach, A and Ugurbil, K and Uludag, K} } @Poster { 4474, title = {Extravascular BOLD Effect for Different Size Blood Vessels Over a Large Range of Magnetic Fields}, year = {2007}, month = {5}, volume = {2007}, number = {60}, pages = {258}, abstract = {The blood oxygenation level dependent (BOLD) signal depends on physiological changes which affect the signal behavior of protons both in the intra- and extravascular tissue space. The functional dependency of the extravascular signal on the oxygenation fraction Y and on cerebral blood volume (CBV) can currently only be evaluated by numerical simulations. We provide analytical expressions for relaxation rates R2* and R2 depending on Y, B0 up to 9.4 T, and CBV for different size cylinders (approx. 3, 6, 20 \(\mu\)m). These results allow to model stimulus evoked BOLD signal changes for GRE and SE at different field strengths.}, department = {Department MRZ}, web_url = {http://www.ismrm.org/07/}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, event_place = {Berlin, Germany}, event_name = {2007 Joint Annual Meeting ISMRM-ESMRMB}, language = {en}, author = {Uludag, K and M{\"u}ller-Bierl, BM and Ugurbil, K} } @Poster { 4933, title = {Insights into the dynamics of hemodynamic response to millisecond stimulus duration: A fMRI and VEP combination study}, year = {2007}, month = {5}, volume = {2007}, number = {191}, pages = {39}, abstract = {In a previous study, we observed that the intercept of BOLD integral at 0ms stimulus duration was not zero. This suggests, below specific stimulus duration the hemodynamic response remains constant. In order to gain insights about the dynamics of BOLD and neural response at ultrashort stimulus durations (0.1 to 5ms), we performed a VEP and fMRI combination study. We have observed that a) a hemodynamic response to 0.1 ms stimulus duration is detectable in human subjects b) both BOLD integral and VEP amplitude increase monotonically with increasing stimulus duration and c) they show nearly similar nonlinearities.}, department = {Department MRZ}, web_url = {http://www.ismrm.org/07/}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, event_place = {Berlin, Germany}, event_name = {2007 Joint Annual Meeting ISMRM-ESMRMB}, language = {en}, author = {Yesilyurt, B and Whittingstall, K and Ugurbil, K and Uludag, K} } @Poster { 4476, title = {Magnetic field distribution and signal decay in fMRI using the dipole model and Monte Carlo diffusion modeling}, year = {2007}, month = {5}, volume = {2007}, number = {3244}, pages = {624}, abstract = {the presence of a susceptibility distribution. Dynamic processes (Brownian motion) are taken into account using additionally a Monte Carlo (MC) method for the positioning of the protons. Signal decay computation inside a model of brain parenchyma was found to depend on the evaluation procedure of the signal decay. MC modeling leads to signal decay characteristics depending on geometry and blood deoxygenation inside the vessel. Intra- and extravascular signal decay contributions can be determined individually.}, url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/ISMRM2007-MuellerBierl_4476[0].pdf}, department = {Department MRZ}, web_url = {http://www.ismrm.org/07/}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, event_place = {Berlin, Germany}, event_name = {2007 Joint Annual Meeting ISMRM-ESMRMB}, language = {en}, author = {M{\"u}ller-Bierl, BM and Uludag, K and Pereira, PL and Schick, F} } @Poster { 4392, title = {Extravascular fMRI R2/R2*-Dependency on Vessel-Radius, and Fill Factor using Monte-Carlo (MC) Modelling}, year = {2006}, month = {10}, department = {Department MRZ}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, event_place = {Grenoble, France}, event_name = {International Topical Meeting on Microwave Photonics (MWP '06).}, language = {en}, author = {M{\"u}ller-Bierl, BM and Uludag, K and Schick, F} } @Poster { 4932, title = {Blood Oxygenation Level Dependent (BOLD) Signal Response to Stimulus Duration of 1 ms is Measurable in Human Subjects}, journal = {Magnetic Resonance Materials in Physics, Biology and Medicine}, year = {2006}, month = {9}, volume = {19}, number = {Supplement 1}, pages = {307}, abstract = {In a previous study, we have shown that in human subjects it is possible to detect blood oxygenation level dependent (BOLD) signal changes evoked by a visual stimulus presented only for 5 ms. Moreover, we observed that at this ultrashort stimulus duration a) the response is highly non-linear compared to 50ms, 250ms and 1s stimulus b) the extrapolated intercept at 0ms stimulus duration was not zero suggesting that below a specific stimulus duration the hemodynamic response remains constant}, department = {Department MRZ}, web_url = {http://www.springerlink.com/content/n70r05532r7q6425/fulltext.pdf}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, event_place = {Warsaw, Poland}, event_name = {23rd Annual Scientific Meeting of the ESMRMB 2006}, language = {en}, DOI = {10.1007/s10334-006-0043-1}, author = {Yesilyurt, B and Ugurbil, K and Uludag, K} } @Poster { 4391, title = {Functional Magnetic Resonance Imaging based BCI for Neurorehabilitation}, year = {2006}, month = {9}, department = {Department MRZ}, web_url = {https://online.tugraz.at/tug_online/vag.detail?vid=33572}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, event_place = {Graz, Austria}, event_name = {3rd International Brain-Computer Interface Workshop and Training Course 2006}, language = {en}, author = {Sitaram, R and Caria, A and Veit, R and Uludag, K and Gaber, T and K{\"u}bler, A and Birbaumer, N} } @Poster { 4393, title = {Anterior Cingulate Hypoactivity in Criminal Sexual Offenders during Succesful and Failed Response Inhibition}, journal = {Neuroimage}, year = {2006}, month = {6}, volume = {31}, number = {Supplement 1}, pages = {S84}, department = {Department MRZ}, web_url = {http://www.sciencedirect.com/science/article/pii/S1053811906004575}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, event_place = {Firenze, Italy}, event_name = {12th Annual Meeting of the Organization for Human Brain Mapping (HBM 2006)}, language = {en}, DOI = {10.1016/j.neuroimage.2006.04.176}, author = {Gaber, TJ and K{\"u}bler, A and Veit, R and Caria, A and Leo, S and Uludag, K and Birbaumer, N and Sitaram, R} } @Poster { 4931, title = {Hemodynamic Response to 0,1 ms (at 7T) and 1 ms (at 3T) Stimulus is Detectable in Human Subjects}, journal = {Neuroimage}, year = {2006}, month = {6}, volume = {31}, number = {Supplement 1}, pages = {S47}, abstract = {In a previous study, we have shown that in humans it is possible to detect blood oxygenation level dependent (BOLD) signal changes evoked by a visual stimulus presented only for 5 ms. Moreover, we observed that the extrapolated intercept at 0ms stimulus duration was not zero suggesting that below a specific stimulus duration the hemodynamic response remains constant. In this study, we have expanded our previous investigation on the temporal behavior of the BOLD response by zooming into the time scale of stimulus durations as short as 0,1 to 5ms (at 7T) and 1 to 5ms (at 3T), in order to evaluate if there is indeed a minimum hemodynamic response.}, url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/POSTER_HBM_2006_4931[0].pdf}, department = {Department MRZ}, web_url = {http://www.sciencedirect.com/science/article/pii/S1053811906004575}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, event_place = {Firenze, Italy}, event_name = {12th Annual Meeting of the Organization for Human Brain Mapping (HBM 2006)}, language = {en}, DOI = {10.1016/j.neuroimage.2006.04.176}, author = {Yesilyurt, B and Ugurbil, K and Uludag, K} } @Poster { 4389, title = {Modulation of the post-stimulus undershoot of the BOLD signal independent of the positive response}, journal = {Neuroimage}, year = {2006}, month = {6}, volume = {31}, number = {Supplement 1}, pages = {S47}, department = {Department MRZ}, web_url = {http://www.sciencedirect.com/science/article/pii/S1053811906004575}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, event_place = {Firenze, Italy}, event_name = {12th Annual Meeting of the Organization for Human Brain Mapping (HBM 2006)}, language = {en}, DOI = {10.1016/j.neuroimage.2006.04.176}, author = {Sadaghiani, S and Thielscher, A and Ugurbil, K and Uludag, K} } @Poster { 4390, title = {Near infrared spectroscopy based brain-computer interface}, journal = {Neuroimage}, year = {2006}, month = {6}, volume = {12}, number = {Supplement 1}, pages = {S32}, department = {Department MRZ}, web_url = {http://www.sciencedirect.com/science/article/pii/S1053811906004575}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, event_place = {Firenze, Italy}, event_name = {12th Annual Meeting of the Organization for Human Brain Mapping (HBM 2006)}, language = {en}, DOI = {10.1016/j.neuroimage.2006.04.176}, author = {Sitaram, R and Haihong, Z and Uludag, K and Cuntai, G and Hoshi, Y and Birbaumer, N} } @Poster { VeitLCGSUB2006, title = {Real-time fMRI of human anterior insula during emotional processing}, journal = {Neuroimage}, year = {2006}, month = {6}, volume = {31}, number = {Supplement 1}, pages = {S154}, department = {Department MRZ}, web_url = {http://www.sciencedirect.com/science/article/pii/S1053811906004575}, event_place = {Firenze, Italy}, event_name = {12th Annual Meeting of the Organization for Human Brain Mapping (HBM 2006)}, DOI = {10.1016/j.neuroimage.2006.04.176}, author = {Veit, R and Lotze, M and Caria, A and Gaber, T and Sitaram, R and Uludag, K and Birbaumer, N} } @Poster { 4362, title = {Hemodynamics and nonlinearities of BOLD response to ultrashort visual stimulation (5ms - 1s)}, year = {2006}, month = {5}, volume = {14}, number = {2784}, pages = {535}, abstract = {It has generally been suggested that one cannot temporally resolve alterations in neural activity in the range of milliseconds using BOLD signal since hemodynamic response evolves in seconds. However, in this study using ultrashort visual stimulus durations ranging from 5 milliseconds to 1 second we investigated the hemodynamic response and nonlinearity of BOLD response. We were able to show that 1) a BOLD response to stimulus durations as short as 5 ms is detectable in humans; b) BOLD responses to different stimulus durations are highly non-linear and c) non-linearities depend not only to stimulus duration but also on intensity.}, url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/abstract_ismrm_2006_[0].pdf}, department = {Department MRZ}, web_url = {http://www.ismrm.org/06/}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, event_place = {Seattle, WA, USA}, event_name = {14th Scientific Meeting of the International Society of Magnetic Resonance in Medicine (ISMRM 2006)}, language = {en}, author = {Uludag, K and Yesilyurt, B and Ugurbil, K} } @Miscellaneous { 5328, title = {Funktionelle Magnetresonanztomographie und transkranielle Magnetstimulation: wie die Kombination zweier Methoden neue R{\"u}ckschl{\"u}sse {\"u}ber die Funktionsweise des Gehirns erlaubt}, journal = {Jahrbuch der Max-Planck-Gesellschaft}, year = {2006}, volume = {2007}, pages = {337-341}, abstract = {In the last two decades, the development of functional magnetic resonance imaging (fMRI) substantially contributed to the progress of human cognitive neuroscience. Because fMRI assesses neuronal activity indirectly, only limited causal statements about brain processes can be made. In the following, it is shown exemplarily by combining fMRI and transcranial magnetic stimulation (TMS) how this limitation can be overcome. Thus, multimodal brain imaging methods offer new opportunities for the exploration of the human brain.}, url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/Jahrbuch2007-Thielscher_[0].pdf}, department = {Department MRZ}, web_url = {http://cms.mpg.de/mpg-export/mpg/website/bilderBerichteDokumente/dokumentation/jahrbuch/2007/biologische_kybernetik/forschungsSchwerpunkt/index.html}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, language = {de}, author = {Thielscher, A and Uludag, K and Ugurbil, K} } @Conference { 5938, title = {Insights into the dynamics of hemodynamic response to millisecond stimulus duration: A fMRI and VEP study}, year = {2007}, month = {5}, abstract = {In a previous study, we have shown that in human subjects it is possible to detect blood oxygenation level dependent (BOLD) signal changes evoked by a visual stimulus presented only for 5 ms. Moreover, we observed that at this ultrashort stimulus duration a) the response is highly non-linear compared to 50ms, 250ms and 1s stimulus b) the extrapolated intercept at 0ms stimulus duration was not zero. That is, below specific stimulus duration the hemodynamic response remains constant. In this study, we have expanded our previous investigation on the temporal behaviour of the BOLD response by zooming into the time scale of stimulus durations as short as 0.1 to 5ms, in order to evaluate if there is indeed a minimum hemodynamic response. Moreover, in order to gain insights about the dynamics of neural response at ultrashort stimulus durations, we also performed VEP recordings to complement the fMRI data.}, url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/BARIS_YESILYURT_ISMRM_2007_PRESENTATION_[0].pdf}, department = {Department MRZ}, talk_type = {Abstract Talk}, web_url = {http://www.ismrm.org/07/}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, event_place = {Berlin, Germany}, event_name = {2007 Joint Annual Meeting ISMRM-ESMRMB}, language = {en}, author = {Yesilyurt, B and Whittingstall, K and Ugurbil, K and Uludag, K} } @Conference { 3841, title = {Influence of moderate hypercapnia on neural activity in monkey by simultaneous intracortical recordings and fMRI at 4.7T}, year = {2005}, month = {11}, volume = {35}, number = {10.11}, abstract = {Cerebral metabolic rate of oxygen (CMRO2) can be obtained with magnetic resonance imaging (MRI) by calibrating BOLD using hypercapnia. CO2 administration influences BOLD by increasing and eventually stabilizing blood flow and volume respectively. This leaves blood oxygenation as the predominating (if not the only) factor affecting the magnitude of BOLD. Obviously, the above assortment implies that CO2 increase acts exclusively as vasoactive agent, without affecting neuronal activity and hence oxygen metabolism. Amongst others, the latter assumption was strengthened by the results of Schmidt and Kety in the 50s. Most of the fMRI studies report coupling of cerebral blood flow (CBF) and oxygen metabolism (the ratio of fractional changes in CBF and CMRO2 is n = 2). In this study we investigated the dependence of neural activity on enhanced CO2 concentration by means of simultaneous intracortical recordings and BOLD imaging in the anesthetized macaque monkey.}, department = {Department Logothetis}, talk_type = {Abstract Talk}, web_url = {http://www.sfn.org/absarchive/}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, event_place = {Washington, DC, USA}, event_name = {35th Annual Meeting of the Society for Neuroscience (Neuroscience 2005)}, language = {en}, author = {Zappe, A-CC and Uludaq, K and Rainer, G and Logothetis, NK} }