% % This file was created by the Typo3 extension % sevenpack version 0.7.14 % % --- Timezone: CEST % Creation date: 2013-05-26 % Creation time: 10-55-17 % --- Number of references % 10 % @Article { 4898, title = {Capillary hydrophilic interaction chromatography/mass spectrometry for simultaneous determination of multiple neurotransmitters in primate cerebral cortex.}, journal = {Rapid Communications in Mass Spectrometry}, year = {2007}, month = {11}, volume = {21}, number = {22}, pages = {3621-3628}, abstract = {A diverse array of neurotransmitters and neuromodulators control and affect brain function. A profound understanding of the signaling pathways and the neural circuits underlying behavior is therefore likely to require the tracking of concentration changes of active neurochemicals. In the present study, we demonstrate the feasibility of a method allowing the simultaneous determination of the concentrations of six neurotransmitters: acetylcholine, serotonin, dopamine, gamma-aminobutyric acid (GABA), glutamate and aspartate, in the extracellular brain fluid (EBF). We used hydrophilic interaction chromatography (HILIC) coupled to tandem mass spectrometry (MS/MS) to analyze the EBF from the monkey brain. A push-pull sampling method was used to collect EBF from the prefrontal cortex (PFC) of conscious monkeys at flow rates in the range of low nL/min. The detection limits of acetylcholine, serotonin, dopamine, GABA, glutamate and aspartate were 0.015, 0.15, 0.3, 1.2, 6 and 15 femtomoles, respectively, allowing us to quantitatively determine the concentrations of these six neurotransmitters simultaneously from 500 nL in vivo samples. We conclude that HILIC/MS/MS combined with the push-pull sampling method represents a sensitive technique for simultaneous monitoring of neurotransmitters from EBF samples.}, department = {Department Logothetis}, web_url = {http://www3.interscience.wiley.com/cgi-bin/fulltext/116330811/PDFSTART}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, language = {en}, DOI = {10.1002/rcm.3251}, author = {Zhang, X and Rauch, A and Lee, H and Xiao, H and Rainer, G and Logothetis, NK} } @Article { 2998, title = {Phase locking of single neuron activity to theta oscillations during working memory in monkey extrastriate visual cortex}, journal = {Neuron}, year = {2005}, month = {1}, volume = {45}, number = {1}, pages = {147-156}, abstract = {Working memory has been linked to elevated single neuron discharge in monkeys and to oscillatory changes in the human EEG, but the relation between these effects has remained largely unexplored. We addressed this question by measuring local field potentials and single unit activity simultaneously from multiple electrodes placed in extrastriate visual cortex while monkeys were performing a working memory task. We describe a significant enhancement in theta band energy during the delay period. Theta oscillations had a systematic effect on single neuron activity, with neurons emitting more action potentials near their preferred angle of each theta cycle. Sample-selective delay activity was enhanced if only action potentials emitted near the preferred theta angle were considered. Our results suggest that extrastriate visual cortex is involved in short-term maintenance of information and that theta oscillations provide a mechanism for structuring the recurrent interaction between neurons in different brain regions that underlie working memory.}, department = {Department Logothetis}, web_url = {http://www.sciencedirect.com/science?_ob=MImg\&_imagekey=B6WSS-4F60R7J-J-1\&_cdi=7054\&_user=29041\&_orig=search\&_coverDate=01\%2F06\%2F2005\&_sk=999549998\&view=c\&wchp=dGLbVlb-zSkzk\&md5=45afc4ed88ce3da9e7774562c098a39f\&ie=/sdarticle.pdf}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, language = {en}, DOI = {10.1016/j.neuron.2004.12.025}, author = {Lee, H and Simpson, GV and Logothetis, NK and Rainer, G} } @Article { 2518, title = {Working-memory related theta (4-7Hz) frequency oscillations observed in monkey extrastriate visual cortex}, journal = {Neurocomputing}, year = {2004}, month = {6}, volume = {58-60}, number = {Computational Neuroscience: Trends in Research 2004}, pages = {965-969}, abstract = {Workingmemory has been linked to elevated activity in single neurons in monkeys, as well as to oscillatory phenomena in the human EEG. To understand the relation between these findings, we explore here whether working-memoryoscillations can also be observed in monkeycortex. We indeed found working-memoryrelatedoscillations in the thetafrequency band in monkeyvisualcortex, which were correlated to monkeys’ behavioral performance on a contrast discrimination task. We discuss possible functional interpretations of this finding.}, department = {Department Logothetis}, web_url = {http://www.sciencedirect.com/science/article/pii/S0925231204001584}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, DOI = {10.1016/j.neucom.2004.01.153}, author = {Rainer, G and Lee, H and Simpson, GV and Logothetis, NK} } @Article { 2517, title = {The Effect of Learning on the Function of Monkey Extrastriate Visual Cortex}, journal = {PLoS Biology}, year = {2004}, month = {2}, volume = {2}, number = {2}, pages = {275-283}, abstract = {One of the most remarkable capabilities of the adult brain is its ability to learn and continuously adapt to an ever-changing environment. While many studies have documented how learning improves the perception and identification of visual stimuli, relatively little is known about how it modifies the underlying neural mechanisms. We trained monkeys to identify natural images that were degraded by interpolation with visual noise. We found that learning led to an improvement in monkeys' ability to identify these indeterminate visual stimuli. We link this behavioral improvement to a learning-dependent increase in the amount of information communicated by V4 neurons. This increase was mediated by a specific enhancement in neural activity. Our results reveal a mechanism by which learning increases the amount of information that V4 neurons are able to extract from the visual environment. This suggests that V4 plays a key role in resolving indeterminate visual inputs by coordinated interaction between bottom-up and top-down processing streams.}, department = {Department Logothetis}, web_url = {http://www.plosbiology.org/article/fetchObjectAttachment.action?uri=info\%3Adoi\%2F10.1371\%2Fjournal.pbio.0020044\&representation=PDF}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, DOI = {10.1371/journal.pbio.0020044}, EPUB = {e44}, author = {Rainer, G and Lee, H and Logothetis, NK} } @Poster { 3163, title = {Generalization of neural selectivity across spatial scale in monkey extrastriate area V4}, year = {2004}, month = {10}, volume = {34}, number = {751.3}, abstract = {Lesions of area V4 lead to impairments in size discrimination. To study the involvement of single V4 neurons in generalization across spatial scale, we trained monkeys on a modified delayed matching-to-sample task. On each trial, one of five novel natural scenes was briefly shown at the center of gaze at one of three sizes (small: 6\(^{\circ}\)\(\times\)6\(^{\circ}\), medium 10\(^{\circ}\)\(\times\)10\(^{\circ}\) and large 15\(^{\circ}\)\(\times\)15\(^{\circ}\)). After a delay of 1 second a probe object (always at medium size) was presented and monkeys had to report if it matched the sample. We found behavioral evidence for partial generalization across spatial scale. Monkeys’ performance was best for medium size samples (92\% correct). Paired t-tests (evaluated at P<.05) showed that performance was significantly lower for both small (73\% correct) and large (80\% correct), but greater than chance performance (50\% correct). We have preliminary data from 34 neurons recorded in one monkey. Quantitative receptive field spot mapping revealed that the receptive field centers of most neurons were within 4 degrees of the fixation point. Most (25/34 or 74\%) neurons distinguished in terms of their sample evoked activity among the sample stimuli at one or more of the three spatial scales (ANOVAs evaluated at P<0.05). We used a correlation analysis to evaluate how well neurons generalized across spatial scale, by comparing tuning functions for small and large stimuli to the tuning functions for the standard medium size. We found that on average neurons appeared to generalize to both larger and smaller stimuli (mean correlation coefficients: 0.62 for larger size, 0.38 for smaller size). For about a quarter of these neurons (6/25 or 24\%) correlation coefficients were greater than 0.8 for both size increases and decreases suggesting robust generalization to both smaller and larger sizes. The results reveal extent and limits of generalization across image size at the level of single neurons in extrastriate area V4.}, department = {Department Logothetis}, web_url = {http://www.sfn.org/absarchive/}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, event_place = {San Diego, CA, USA}, event_name = {34th Annual Meeting of the Society for Neuroscience (Neuroscience 2004)}, author = {Lee, H and Logothetis, NK and Rainer, G} } @Poster { RainerLL2004, title = {The contribution of color and luminance to the neural response to natural images in extrastriate area V4}, year = {2004}, month = {7}, number = {A052.8-307}, abstract = {Extrastriate visual area V4 is thought to play an important role in color processing. To study how color and luminance affect activity of V4 neurons, we decomposed colored natural images (I) into chrominance (C) and luminance (L) parts, such that the images can be reconstructed as the sum of these two contributions (i. e. I=L+C). In addition, we also studied their response to grayscale versions of the colored natural image stimuli. We have preliminary data from 82 V4 neurons. We used eight natural images as stimuli, which were 10 by 10 deg in size and presented for 300ms while monkeys were maintaining central fixation. Average neural activity was similar for colored and black \& white versions of the natural image stimuli, while luminance (L) and chrominance (C) contributions elicited greater and less average activity, respectively. Analysis of neural selectivity revealed that V4 neurons were on average significantly more selective for colored than black \& white natural images, and that selectivity for both the L and C components of these images was significantly lower. These results help clarify the importance of color for neural activity in extrastriate visual cortex.}, department = {Department Logothetis}, web_url = {http://fens2004.neurosciences.asso.fr/}, event_place = {Lisboa, Portugal}, event_name = {4th Forum of European Neuroscience (FENS 2004)}, author = {Rainer, G and Lee, H and Logothetis, NK} } @Poster { 3162, title = {Working Memory Related Neuronal Activity and Theta Oscillations in Extrastriate V4}, year = {2004}, month = {2}, volume = {7}, pages = {131}, abstract = {Working memory is used to store information for brief periods. The mechanism of working memory is studied in both humans and monkeys. While in monkeys working memory is thought to depend on elevated ring activity in prefrontal cortex during the memory period of a cognitive task, EEG studies in humans have linked oscillations to working memory not only in the frontal but also in the occipital cortex. It is not known, whether these two ndings -the delay activity and the oscillatory phenomena- interact with each other and how they may support working memory. We addressed this issue by recording simultaneously single unit activity (SUA) and local eld potentials (LFP) from an occipital brain region -area V4- in monkeys. The monkeys had to perform a delayed-matching-to-sample task. The task started with a 1000 ms xation period, followed by a 300 ms presentation of a sample object. After a delay of 1000 ms a probe object was presented and the monkeys had to decide whether the probe matched the sample by releasing a lever. The objects were natural images of the size 10 f x10 f . The sample stimuli had contrast levels between 5\% and 100\%, while the probe objects were always at 100\% contrast. The monkeys' performance was almost at ceiling for contrast levels higher than 25\% and at chance for low contrast levels. We compared the delay period to the xation period by assessing power in the theta band of the LFP during the last 800 ms of the delay and the xation respectively. Compared to the xation period we observed increased theta oscillations for high contrast stimuli at many recording sites during the delay. Almost all sites showed reduced theta oscillations at 5\% contrast level, when the monkeys were performing at chance. Unlike in prefrontal cortex there was no elevated neuronal activity during the delay period. SUA during the delay was similar to values during the xation. But examining at the relationship between theta phase and SUA, we found that many neurons red preferentially at a particular phase of the theta cycle. These ndings suggest that theta oscillations increase during the delay period in visual cortex, and that these oscillations serve to structure neuronal activity.}, department = {Department Logothetis}, web_url = {http://www.twk.tuebingen.mpg.de/twk04/index.php}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, event_place = {T{\"u}bingen, Germany}, event_name = {7th T{\"u}bingen Perception Conference (TWK 2004)}, author = {Lee, H and Rainer, G and Logothetis, NK} } @Poster { 3161, title = {Phase locking of single neuron activity to theta oscillations during working memory in monkey extrastriate visual cortex}, year = {2003}, month = {11}, volume = {33}, number = {385.20}, abstract = {Several studies in humans have linked oscillations in frontal and occipital cortex with working memory. In monkeys, working memory is thought to depend on delay actitity - elevated firing of neurons in prefrontal and other cortical areas. Whether or how these oscillatory phenomena and delay activity interact to support working memory is unknown. To address this question, we recorded both single-unit activity (SUA) and local field potentials (LFP) simultaneously from multiple sites in area V4. Monkeys performed a delayed-matching-to-sample task. After a 1sec fixation period, a sample object was briefly presented (300ms). Following a 1sec delay, a probe object was presented and monkeys had to release a lever if the probe matched the sample. Natural images (10\(^{\circ}\)x10\(^{\circ}\) at center of gaze) of varying contrast were used a sample stimuli, probe stimuli were always at full contrast. Monkeys performed above 90\% correct at contrasts of 25\% and higher, and near chance at low contrast. We assessed power in the theta band during the last 700ms of the delay period, and compared this to a similar period during fixation. Almost all sites showed a marked reduction of theta oscillations at 5\% contrast, when monkeys were unable to discriminate the sample stimuli. We observed increased theta oscillations during the delay at many sites for contrasts of 25\% and higher, where monkeys were performing accurately. Examining the relationship between theta phase and single unit activity, we found that many single neurons fired preferentially at a particular phase of the theta cycle. These findings suggest that increases in theta oscillations are present in monkey visual cortex during delays, and that these oscillations serve to structure single unit activity.}, department = {Department Logothetis}, web_url = {http://www.sfn.org/index.aspx?pagename=annualmeeting_futureandpast}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, event_place = {New Orleans, LA, USA}, event_name = {33rd Annual Meeting of the Society for Neuroscience (Neuroscience 2003)}, author = {Lee, H and Simpson, GV and Logothetis, NK and Rainer, G} } @Poster { 953, title = {Psychophysikalische Studien zur Lerninvarianz von Objekten}, year = {2002}, month = {2}, volume = {5}, pages = {87}, abstract = {dass durch das Lernen Generalisierungen entlang bestimmter Stimulusdimensionen stattfinden. In unseren Experimenten untersuchen wir solche Invarianzen des visuellen Lernens in Affen mit nat{\"u}rlichen Objekten. Dazu wurden Makaken trainiert, einen delayed matching-to-sample (DMS) task auszuf{\"u}hren: Den Affen wurde in jedem Durchgang kurz ein Testobjekt pr{\"a}sentiert und nach einer kurzen Verz{\"o}gerung ein Vergleichsobjekt. Die Affen mussten entscheiden ob das Vergleichsobjekt identisch mit dem Testobjekt war oder nicht und dementsprechend einen Hebel loslassen. Die Testobjekte wurden systematisch mit Rauschen interpoliert, w{\"a}hrend die Vergleichsobjekte unmanipuliert blieben. Die Wahrnehmungsleistung der Affen nahm mit zunehmenden Rauschen ab. In jeder Sitzung wurden sowohl bekannte Objekte, die jedesmal gezeigt wurden, als auch neue, unbekannte Objekte gezeigt. Im Vergleich zu den neuen Objekten konnten bekannte Objekte unter st{\"a}rkerem Rauschen identifiziert werden, d.h. die Affen besa{\ss}en f{\"u}r bekannte Objekte eine niedrigere Schwelle. Zus{\"a}tzlich zeigte sich w{\"a}hrend des Trainings, dass die Affen f{\"u}r stark verrauschte Testobjekte, die f{\"u}r sie nicht identifizierbar waren, ein individuell ausgepr{\"a}gtes, stereotypes Verhalten an den Tag legten. Die Affen hatten n{\"a}mlich eine Tendenz f{\"u}r neue Vergleichsobjekte den Hebel viel {\"o}fter loszulassen als f{\"u}r bekannte Vergleichsobjekte. Dies f{\"u}hrte zu systematischen Ver{\"a}nderungen der psychometrischen Funktion. Wir entwickelten eine Methode, mit der die psychometrische Funktion bez{\"u}glich dieser Antwortpr{\"a}ferenz (“response bias”) korrigiert werden kann. Den erfahrungsbedingten Unterschied in der Wahrnehmungsleistung nutzten wir, um systematisch zu untersuchen, f{\"u}r welche Objekteigenschaften visuelles Lernen generalisiert. Dazu wurden zwischen den Trainingssitzungen Testsitzungen eingef{\"u}gt, in denen jeweils eine bestimmte Eigenschaft der Objekte ver{\"a}ndert wurde. Durch den Vergleich von Test- und Trainingssitzungen l{\"a}sst sich zeigen, ob eine bestimmte Objekteigenschaft relevant f{\"u}r das visuelle Lernen ist oder nicht. Vorl{\"a}ufige Daten von einem Affen mit gespiegelten und gr{\"o}ssenver{\"a}nderten Objekten belegen, dass visuelles Lernen bez{\"u}glich dieser Manipulationen teilweise invariant ist.}, department = {Department Logothetis}, web_url = {http://www.twk.tuebingen.mpg.de/twk02/}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, event_place = {T{\"u}bingen, Germany}, event_name = {5. T{\"u}binger Wahrnehmungskonferenz (TWK 2002)}, author = {Lee, H and Rainer, G and Logothetis, NK} } @Poster { 962, title = {Using noise to test invariances of visual learning in the macaque}, year = {2001}, month = {11}, volume = {31}, number = {188.1}, abstract = {Human psychophysics has shown that some perceptual learning effects are invariant with respect to stimulus manipulations, for example changes in object size. Here, we examine invariances of visual object learning in the macaque monkey. Monkeys were first trained on regular sessions of a delayed-matching-to-sample task, in which they were briefly presented with a sample object, which was parametrically degraded with various amounts of visual noise. After a brief delay, an undegraded test object was presented, and monkeys had to release a lever if the test object matched the sample. Performance on this task decreased systematically as more and more noise was added to the stimuli. In addition, thresholds were significantly lower for identifying highly familiar objects in the presence of noise compared to novel objects, which the monkeys had not seen before. Thus, repeated experience with a particular set of objects allowed monkeys to identify them in the presence of greater amounts of noise compared to novel objects. We used this experience-dependent difference in psychophysical performance to study learning invariances, by interspersing test sessions among the regular sessions described above. In test sessions, a systematic change was made to the objects. By comparing performance to regular session, we are able to assess whether visual learning is affected by a given stimulus manipulation. We have preliminary data (4 sessions) from one monkey with mirror-reversed objects, which indicates that mirror reversal leads to psychophysical performance intermediate between the trained views and novel objects. In addition, we are examining the effects of changes in size and visual field position.}, department = {Department Logothetis}, web_url = {http://www.sfn.org/index.aspx?pagename=abstracts_ampublications}, institute = {Biologische Kybernetik}, organization = {Max-Planck-Gesellschaft}, event_place = {San Diego, CA, USA}, event_name = {31st Annual Meeting of the Society for Neuroscience (Neuroscience 2001)}, author = {Lee, H and Rainer, G and Hengstenberg, R and Logothetis, NK} }