9263KSSaleemJPaulsMAAugathTTrinathBAPrauseTHashikawaNKLogothetis2002-05-00534685700Recently, an MRI-detectable, neuronal tract-tracing method in living animals was introduced that exploits the anterograde transport of manganese (Mn2+). We present the results of experiments simultaneously tracing manganese chloride and wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) to evaluate the specificity of the former by tracing the neuronalconnections of the basal ganglia of the monkey. Mn2+ and WGA-HRP yielded remarkably similar and highly specific projection patterns. By showing the sequential transport of Mn2+ from striatum to pallidum-substantia nigra and then to thalamus, we demonstrated MRI visualization of transport across at least one synapse in the CNS of the primate. Transsynaptic tract tracing in living primates will allow chronic studies of development and plasticity and provide valuable anatomical information for fMRI and electrophysiological experiments in primates.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published15Magnetic Resonance Imaging of Neuronal Connections in the Macaque Monkey15017154218833NKLogothetisJPaulsMAAugathTTrinathAOeltermann2001-07-006843412150157Functional magnetic resonance imaging (fMRI) is widely used to study the operational organization of the human brain, but the exact relationship between the measured fMRI signal and the underlying neural activity is unclear. Here we present simultaneous intracortical recordings of neural signals and fMRI responses. We compared local field potentials (LFPs), single- and multi-unit spiking activity with highly spatio-temporally resolved blood-oxygen-level-dependent (BOLD) fMRI responses from the visual cortex of monkeys. The largest magnitude changes were observed in LFPs, which at recording sites characterized by transient responses were the only signal that significantly correlated with the haemodynamic response. Linear systems analysis on a trial-by-trial basis showed that the impulse response of the neurovascular system is both animal- and site-specific, and that LFPs yield a better estimate of BOLD responses than the multi-unit responses. These findings suggest that the BOLD contrast mechanism reflects the input and intracortical processing of a given area rather than its spiking output.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published7Neurophysiological investigation of the basis of the fMRI signal15017154212043NKLogothetisHGuggenbergerSPeledJPauls1999-06-0062555562Functional magnetic resonance imaging (fMRI) has become an essential tool for studying human brain function. Here we describe the application of this technique to anesthetized monkeys. We present spatially resolved functional images of the monkey cortex based on blood oxygenation level dependent (BOLD) contrast. Checkerboard patterns or pictures of primates were used to study stimulus-induced activation of the visual cortex, in a 4.7-Tesla magnetic field, using optimized multi-slice, gradient-recalled, echo-planar imaging (EPI) sequences to image the entire brain. Under our anesthesia protocol, visual stimulation yielded robust, reproducible, focal activation of the lateral geniculate nucleus (LGN), the primary visual area (V1) and a number of extrastriate visual areas, including areas in the superior temporal sulcus. Similar responses were obtained in alert, behaving monkeys performing a discrimination task.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published7Functional imaging of the monkey brain15017154219093NKLogothetisJPauls1995-05-0035270288A key question concerning the perception of 3D objects is the spatial reference frame used by the brain to represent them. The celerity of the recognition process could be explained by the visual system's ability to quickly transform stored models of familiar 3D objects, or by its ability to specify the relationship among viewpoint-invariant features or volumetric primitives that can be used to accomplish a structural description of an image. Alternatively, viewpoint-invariant recognition could be realized by a system endowed with the ability to perform an interpolation between a set of stored 2D templates, created for each experienced viewpoint. In the present study we set out to examine the nature of object representation in the primate in combined psychophysical-electrophysiological experiments. Monkeys were trained to recognize novel objects from a given viewpoint and subsequently were tested for their ability to generalize recognition for views generated by mathematically rotating the objects around any arbitrary axis. The perception of 3D novel objects was found to be a function of the object's retinal projection at the time of the recognition encounter. Recognition became increasingly difficult for the monkeys as the stimulus was rotated away from its familiar attitude. The generalization field for novel wire-like and spheroidal objects extended to about +/- 40 degrees around an experienced viewpoint. When the animals were trained with as few as three views of the object, 120 degrees apart, they could often interpolate recognition for all views resulting from rotations around the same axis. Recordings from inferotemporal cortex during the psychophysical testing showed a number of neurons with remarkable selectivity for individual views of those objects that the monkey had learned to recognize. Plotting the response of neurons as a function of rotation angle revealed systematic view-tuning curves for rotations in depth. A small percentage of the view-selective cells responded strongly for a particular view and its mirror-symmetrical view. For some of the tested objects, different neurons were found to be tuned to different views of the same object; the peaks of the view-tuning curves were 40-50 degrees apart. Neurons were also found that responded to the sight of unfamiliar objects or distractors. Such cells, however, gave nonspecific responses to a variety of other patterns presented while the monkey performed a simple fixation task.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published18Psychophysical and physiological evidence for viewer-centered object representations in the primate9083NKLogothetisJPaulsTPoggio1995-05-0055552563Background: The inferior temporal cortex (IT) of the monkey has long been known to play an essential role in visual object recognition. Damage to this area results in severe deficits in perceptual learning and object recognition, without significantly affecting basic visual capacities. Consistent with these ablation studies is the discovery of IT neurons that respond to complex two-dimensional visual patterns, or objects such as faces or body parts. What is the role of these neurons in object recognition? Is such a complex configurational selectivity specific to biologically meaningful objects, or does it develop as a result of extensive exposure to any objects whose identification relies on subtle shape differences? If so, would IT neurons respond selectively to recently learned views or features of novel objects? The present study addresses this question by using combined psychophysical and electrophysiological experiments, in which monkeys learned to classify and recognize computer-generated three-dimensional objects.
Results A population of IT neurons was found that responded selectively to views of previously unfamiliar objects. The cells discharged maximally to one view of an object, and their response declined gradually as the object was rotated away from this preferred view. No selective responses were ever encountered for views that the animal systematically failed to recognize. Most neurons also exhibited orientation-dependent responses during view-plane rotations. Some neurons were found to be tuned around two views of the same object, and a very small number of cells responded in a view-invariant manner. For the five different objects that were used extensively during the training of the animals, and for which behavioral performance became view-independent, multiple cells were found that were tuned around different views of the same object. A number of view-selective units showed response invariance for changes in the size of the object or the position of its image within the parafovea.
Conclusion Our results suggest that IT neurons can develop a complex receptive field organization as a consequence of extensive training in the discrimination and recognition of objects. None of these objects had any prior meaning for the animal, nor did they resemble anything familiar in the monkey's environment. Simple geometric features did not appear to account for the neurons' selective responses. These findings support the idea that a population of neurons — each tuned to a different object aspect, and each showing a certain degree of invariance to image transformations — may, as an ensemble, encode at least some types of complex three-dimensional objects. In such a system, several neurons may be active for any given vantage point, with a single unit acting like a blurred template for a limited neighborhood of a single view.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published11Shape Representation in the Inferior Temporal Cortex of Monkeys.6783NKLogothetisJPaulsHHBülthoffTPoggio1994-05-0054401414Background: How do we recognize visually perceived three-dimensional objects, particularly when they are seen from novel view-points? Recent psychophysical studies have suggested that the human visual system may store a relatively small number of two-dimensional views of a three-dimensional object, recognizing novel views of the object by interpolation between the stored sample views. In order to investigate the neural mechanisms underlying this process, physiological experiments are required and, as a prelude to such experiments, we have been interested to know whether the observations made with human observers extend to monkeys.Results We trained monkeys to recognize computer-generated images of objects presented from an arbitrarily chosen training view and containing sufficient three-dimensional information to specify the object’s structure. We subsequently tested the trained monkeys’ ability to generalize recognition of the object to views generated by rotation of the target object around any arbitrary axis. The monkeys recognized as the target only those two-dimensional views that were close to the familiar, training view. Recognition became increasingly difficult for the monkeys as the stimulus was rotated away from the experienced viewpoint, and failed for views farther than about 40° from the training view. This suggests that, in the early stages of learning to recognize a previously unfamiliar object, the monkeys build two-dimensional, viewer-centered object representations, rather than a three-dimensional model of the object. When the animals were trained with as few as three views of the object, 120° apart, they could often recognize all the views of the object resulting from rotations around the same axis.Conclusion Our experiments show that recognition of three-dimensional novel objects is a function of the object's retinal projection. This suggests that non-human primates, like humans, may accomplish view-invariant recognition of familiar objects by a viewer-centered system that interpolates between a small number of stored views. The measures of recognition performance can be simulated by a regularization network that stores a few familiar views, and is endowed with the ability to interpolate between these views. Our results provide the basis for physiological studies of object-recognition by monkeys and suggest that the insights gained from such studies should apply also to humans.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published13View-dependent object recognition by monkeys.150171542231747AGrettonAJSmolaOBousquetRHerbrichABelitskiMAugathYMurayamaJPaulsBSchölkopfNKLogothetisBridgetown, Barbados2005-01-00112119We discuss reproducing kernel Hilbert space (RKHS)-based measures of statistical dependence, with emphasis on constrained covariance (COCO), a novel criterion to test dependence of random variables. We show that COCO is a test for independence if and only if the associated RKHSs are universal. That said, no independence test exists that can distinguish dependent and independent random variables in all circumstances. Dependent random variables can result in a COCO which is arbitrarily close to zero when the source densities are highly non-smooth. All current kernel-based independence tests share this behaviour. We demonstrate exponential convergence between the population and empirical COCO. Finally, we use COCO as a measure of joint neural activity between voxels in MRI recordings of the macaque monkey, and compare the results to the mutual information and the correlation. We also show the effect of removing breathing artefacts from the MRI recording.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de//fileadmin/user_upload/files/publications/pdf3174.pdfpublished7Kernel Constrained Covariance for Dependence Measurement150171542015017154219137EBricoloJPaulsNKLogothetisJülich, Germany1995-00-00225242nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published17The Role of Inferior Temporal Cortex in Visual Object Recognition9152JPaulsEBricoloNKLogothetisOxford University PressNew York, NY, USA1996-00-00941nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published32View Invariant Representations in Monkey Temporal Cortex: Position, Scale, and Rotational Invariance91046NKLogothetisJPaulsTPoggio1995-03-0090746NKLogothetisJPaulsTPoggio1994-04-00ShmuelAOPL2004_27AShmuelMAugathAOeltermannJPaulsNKLogothetisSarasota, FL, USA2004-08-0016Background: 1. Numerous studies demonstrated that the response to a stimulus within the classical receptive field is modulated by an additional stimulus outside the receptive field. 2. A recent human fMRI study (Shmuel et al., Neuron 2002) demonstrated a robust sustained negative BOLD response (NBR) beyond the stimulated regions within retinotopic occipital areas. The NBR was associated with decreases in cerebral blood flow (CBF) and oxygen consumption, corroborating that the NBR could be triggered by decreases in neuronal activity. Aims: 1) Are there changes relative to spontaneous activity in non-stimulated regions in V1? 2) What are the neuronal correlates of the negative BOLD response? Methods: Monkeys were visually stimulated with iso-eccentricity rings of rotating checkers that subtended part of the visual-field (VF). A blank gray stimulus was used to measure the baseline cortical signal. Electrical recordings were obtained from the central VF representation in V1 simultaneously with fMRI. Results: Peripheral VF stimulus elicited positive/negative BOLD response in peripheral/more central VF representation in V1. The NBR was associated with decreases in neuronal activity (DsiNA), comparably large in action potentials, in the local-field potential and the multi-unit activity. DsiNA were observed up to 11 mm from the activated region in V1. The onsets of the increases and DsiNA were approximately concurrent, and the onset of the DsiNA preceded the corresponding onset of the NBR. Conclusions: 1) Non-stimulated regions adjacent to active regions in V1 decrease their neuronal activity. 2) The DsinNA cannot be exclusively mediated by the horizontal connections in V1. 3) The NBR in monkey V1 is associated with DsiNA that cannot be caused by hypoxia due to blood steal. 4) Most plausibly, the DsiNA trigger reductions in CBF that cause the NBR.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published-16Decreases in neuronal activity and negative BOLD response in non-stimulated regions of monkey V1150171542127877HBXiaoJPaulsJPfeufferNKLogothetisRiva del Garda, Italy2004-06-00The extracellular compartment of the brain is a complex, dynamic microenvironment
containing nutrients, metabolites, and molecules related to neural signaling. Understanding of
brain function requires direct monitoring of neural activity, commonly done by means of
intracortical microelectrode recordings. The existing extracellular recording techniques
provide us with rich information regarding single or multiple neuron activity as well as some
information about subthreshold processes, but fail to reveal the role of inhibition in the
anatomically demonstrated microcircuits. One possible solution to this is simultaneous
extracellular field potential and neurotransmitter recordings. In this study, an in vivo nanosampling
technique was developed, with significantly higher spatial resolution than that
afforded through microdialysis. The technique capitalizes on its ability to directly withdraw
large quantities (several hundreds of nL) of extracellular fluids (ECF) from the monkey brain
at a rate of 1-50 nL min-1. The fluids were stored along a 4 m long, 20 µm I.D., 90 µm O.D.
fused silica capillary loop. The obtained intact ECF sample was then distributed into a series
of micro-vials according the time interval specified by the systems temporal resolution. The
contents of multiple neurotransmitters and signaling molecules in each distributed ECF
sample, including glutamate, GABA, acetylcholine, and asparagine, were determined
simultaneously by capillary HPLC-MS. Hydrophilic interaction chromatography was
employed to separate the highly polar and ionic compounds directly for mass spectrometer
detection.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de//fileadmin/user_upload/files/publications/pdf2787.pdfpublished0In vivo nano-sampling and capillary liquid chromatography: mass spectrometry analysis of neurotransmitters in the monkey brain150171542145027ASToliasMAugathJPaulsAOeltermannEJTehovnikPHSchillerNKLogothetisNew Orleans, LA, USA2003-11-00Electrical microstimulation has been used extensively to study both neuronal connectivity and the behavioral effects of focal neural excitation. Yet most behaviors involve concurrent activation of several structures that are directly or indirectly interconnected with the stimulated site. Microstimulation performed simultaneously with fMRI offers a unique opportunity to investigate the network of structures eliciting certain behaviors. Recently, simultaneous recording of neural activity and BOLD responses in the monkey has been developed to study the correlation between the fMRI signals and electrical activity in the brain (Logothetis et al., 2001). This work has also enabled us to carry out simultaneous electrical microstimulation and fMRI. The specific goal of the current study is to determine the electrical parameters which elicit activity in the brain similar to that generated by focal visual stimulation. We compared visual stimulation with constant-current charge-balanced biphasic electrical pulses delivered via monopolar microelectrodes placed in area V1. We find that under certain microstimulation parameters we obtain focal activity around the electrode tip in area V1 as well the corresponding retinotopic location in area V2, V3, and MT. Ongoing research examines the activity patterns elicited by stimulating at different cortical layers of V1. This study paves the way to incorporate the much needed anatomical information in the analysis of the electrical signals obtained in trained, awake animals.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published0Simultaneous electrical microstimulation and fMRI in the macaque1501715421FustPAOML20037AFustJPaulsMAugathAOeltermannYMurayamaNKLogothetisNew Orleans, LA, USA2003-11-00The state of unconsciousness during anaesthesia is not characterized by a global disruption of CNS activity. Instead consciousness is mediated by a specific subset of brain states or processes selectively affected by anaesthetics. Our aim is to study the action sites of different types of anaesthetics in the monkey brain (M. mulatta). Here we report on the neural effects of Ketamine, a dissociative anaesthetic acting primarily on the NMDA receptor, and Midazolam, a benzodiazepine affecting GABA(A)-receptors. Ketamine exhibits both inhibitory and excitatory effects at different brain sites. Midazolam, however, is known to increase the GABA(A)-receptor function, and therefore to inhibit cortical activity. To study the primary sites-of-action of these agents in the monkey brain, high-resolution functional magnetic resonance imaging (fMRI) was used to measure stimulus induced activity changes in the alert and anaesthetized monkey. The activity of neurons in visual cortex was recorded during scanning, as well as in separate experiments outside the scanner. Following the acquisition of base-line data, a bolus of the test-substance was applied intravenously via a computerized infusion pump. Brain activity was monitored continuously before, during and after the infusion. The data presented here focus on the effects of anaesthetics on subthreshold and spiking activity and the BOLD-signal. A comparison of the influences on these different neural signals allows studying the site and type of action of anaesthetics in more detail. In addition it has the potential to afford further insights into the neural processes underlying the BOLD-signal.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published0The influence of anaesthetic agents on spiking and subthreshold activity in visual cortex revealed by electrophysiology and high-resolution functional MRI150171542124067AShmuelMAugathAOeltermannJPaulsNKLogothetisNew Orleans, LA, USA2003-11-00Negative BOLD responses (NBRs) are pervasive in human fMRI, but commonly ignored. A recent study (Shmuel et al., Neuron 2002) characterized a robust sustained NBR in the human occipital cortex associated with decreases in cerebral blood flow (CBF) and oxygen consumption, corroborating that the NBR could be triggered by decreases in neuronal activity (DsiNA).
1) Is the NBR associated with DsiNA?
2) Is the origin of the DsiNA vascular (e.g. from hypoxia due to blood steal) or neuronal?
Monkeys were visually stimulated with iso-eccentricity rings composed of rotating checkers. A blank gray stimulus was used to measure the baseline cortical signal.
Similar to the findings in humans, NBR was observed in monkeys: 1) in V1, V2, and V3, 2) in response to stimulation of part of the visual-field (VF), and 3) with a time course anti-correlated to that of the PBR.
To determine the neuronal correlates of the NBR, electrical recordings were obtained from the central VF representation in V1 simultaneously with fMRI. Central/peripheral VF stimulus elicited PBR/NBR in the vicinity of the electrode (Fig. 1). Note that: 1) the NBR was associated with DsiNA, 2) the onsets of the increases and DsiNA were approximately concurrent, and 3) the onset of the DsiNA preceded the corresponding onset of the NBR. The NBR was associated with comparable decreases in both the local-field potential and the multi-unit activity.
The NBR in monkey V1 is associated with DsiNA that could not be caused by blood steal. Most plausibly, the DsiNA trigger reductions in CBF that cause the NBR.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published0The Negative BOLD Response in Monkey V1 is Associated with Decreases in Neuronal Activity150171542120387JPfeufferJPaulsMAAugathTSteudelHMerkleNKLogothetisToronto, Canada2003-07-13349First fMRI results in the awake trained monkey (Macaca mulatta) using a novel vertical 7T/60cm MR system are reported. The setup was custom-designed for MR imaging of monkeys in upright position and simultaneous electrophysiological recording. Using fast gradients and optimized RF coils, the benefits of high magnetic field with increased signal and contrast-to-noise ratio are demonstrated in high-resolution anatomical and functional images.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de//fileadmin/user_upload/files/publications/pdf2038.pdfpublished-349Functional MR imaging of the awake monkey in a novel vertical large-bore 7 Tesla setup150171542124047AShmuelMAAugathAOeltermannJPaulsYMurayamaNKLogothetisNew York, NY, USA2003-06-00e567e568Negative BOLD responses (NBRs; i.e. below baseline) are pervasive in human fMRI experiments, but commonly
ignored. A recent study characterized a robust sustained NBR in the human occipital cortex, triggered by
stimulating part of the visual-field (Shmuel et al., 2002). The NBR depends on the pattern of neuronal activity and
is coupled to the positive BOLD response (PBR). The NBR is correlated with reductions in cerebral blood flow
(CBF) and with decreases in oxygen consumption. The findings from this human study corroborate contributions
to the NBR by 1) a significant component of reduction in neuronal activity and possibly 2) a component of
hemodynamic changes independent of the local changes in neuronal activity.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published0The Negative BOLD Response in Monkey V1 Is Associated with Decreases in Neuronal Activity150171542114827JPaulsNKLogothetisOrlando, FL, USA2002-11-00Identical sensory information often needs to be interpreted and responded to in different ways. For example, identification may require the viewer to pay attention to different information in a visual stimulus than classification. Is task-context-specific processing of a visual stimulus represented in the responses of IT neurons?
We trained two monkeys (macaca mulatta) to perform a classification / identification task in which the animal had to classify or identify a particular stimulus depending on a cue presented at the beginning of the trial.
We analyzed the activity of 356 visually responsive neurons. While the majority of these neurons (65%) responded nearly the same to a stimulus regardless of the task, a considerable population (35%, 126/356) exhibited task-context dependent responses, firing significantly differently to one or more, but never to all, stimuli depending on the task. As a population, task-context dependent neurons fired significantly more during the classification task. A contrast-based selectivity index revealed that these neurons did not respond more selectively to stimuli in the context of the identification task.
In conclusion, IT neurons are more active during classification. Moreover, task-context dependent responses do not appear to be correlated with visual selectivity. A possible explanation for this, perhaps unexpected, effect is that less specificity and broader tuning results in the activation of larger populations which may lead to an increase in the response of individual units during classification. One model of recognition does indeed predict this outcome.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published0Activity of inferior temporal (IT) neurons changes with task context: A comparison of classification and identification150171542115517AAGhazanfarJPaulsDALeopoldMDHauserNKLogothetisOrlando, FL, USA2002-11-00The design of the primate auditory system should reflect the specialized functions that it evolved to carry out. One such function is conspecific vocal recognition. Measuring the neural selectivity to vocalizations is a way to identify the mechanisms underlying this auditory specialization. Previous studies examining call selectivity in the primate auditory cortex suffered from two drawbacks: an impoverished stimulus set and/or the use of anesthetized or passive-listening paradigms. We adopted a simple behavioural task to study how neurons in the rhesus monkey auditory cortex respond to conspecific vocalizations. Two monkeys were trained to listen to sound sequences composed of one or two conspecific vocalizations (mean SPL=79.9 dB) and an artificial horn sound (frequency bandwidth: 788Hz-11kHz; 300ms in duration; SPL=69.7 dB) presented in free-field. They were rewarded if they pulled a lever within 1 sec following the horn sound. Both monkeys were able to do this task at >95%-correct performance levels. This task requires that the monkey attend in the auditory domain without the confounds of over-training on vocalizations and the response lability that occurs during passive-listening. Our stimuli consist of 3 exemplars from each of 7 call categories (coos, pant-threats, grunts, aggressive barks, shrill barks, noisy screams and harmonic arches). Using this paradigm, we are investigating whether the responses of auditory ‘belt’ cortical neurons reflect category-level selectivity to conspecific vocalizations.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published0Neural responses to species-specific vocalizations in the auditory association cortex of the awake behaving rhesus monkey1501715421PrauseSPATHL20027BPrauseKSSaleemJPaulsMAugathTTrinathTHashikawaNKLogothetisHonolulu, HI, USA2002-05-21nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/ISMRM-2002-Prause.pdfpublished0In Vivo MRI of Neuronal Connections in the Macaque Monkey15017154219577IVBondarDALeopoldJMPaulsNKLogothetisTübingen, Germany2002-02-0088Adaptational aftereffects have often been described as the “psychophysicist’s electrode”
because of their ability to isolate specific populations of neurons related to perception.
We have recently demonstrated that adaptational aftereffects can systematically and precisely
bias the perception of complex patterns such as faces (Leopold et al., 2001). These
results suggested a privileged role for the prototype or ‘central tendency’ of an object category
in the representation of faces, which may be expressed in the selective responses of
neurons in the inferotemporal cortex. Specifically, the analysis of a complex sensory pattern
may involve a comparison with a prototype representation implicitly stored in the
sensory apparatus. The present study is a first step to investigating this hypothesis in
alert, behaving, monkeys.
Two monkeys were trained to indicate the identity of up to four individual faces by pressing
one of four buttons. In the first experiment they were shown brief presentations of
faces whose identity was modulated between the mean face and each individual, and
required to identify the face. In the second experiment a 4-second adaptation to a different
face preceded each test face presentation.
Without adaptation, thresholds for discriminating between the memorized faces were
evaluated in both monkeys, and were very similar to those of humans performing the
same task. Following adaptation, perception was biased according to the structure of the
adapting stimulus. The nature and magnitude of the adaptation effects were very similar
to that observed in humans.
These results suggest that mechanisms underlying face recognition in the monkey are
similar to those present in humans, even when it is across species. Current studies are
underway using multielectrode bundles implanted in the inferotemporal cortex of both
monkeys to elucidate the role of the prototype in the neural representation of faces.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published-88Investigation of face representation in monkeys using adaptational aftereffects150171542110627JPaulsNKLogothetisSan Diego, CA, USA2001-11-00In order to investigate the possibility of a more cognitive role for inferior temporal (IT) cortex in visual recognition, we trained two monkeys (macaca mulatta) to perform a classification (CL) / identification (ID) task in which the animal had to classify or identify a particular stimulus depending on a cue presented at the beginning of the trial. Here we compare the responses of neurons in ventral STS and lateral and ventral TE to identical stimuli presented in the context of two different recognition tasks.
Of the 399 neurons recorded to date, roughly 20% were visually responsive to the stimuli presented in the task (86% excitatory, 14% inhibitory). While the majority of neurons (70%) exhibited task-context independent responses, a small population (30%, 23/78) did respond significantly differently to one or more, but never to all, stimuli depending on the task. Closer examination of this population of task-context dependent neurons revealed that the vast majority (21/23) fired more for the stimulus or stimuli for which they showed a significant difference in the context of the CL task. Moreover, only 3 of these cells responded selectively (more than 2:1 over the next best stimulus) to any of the stimuli presented, although 15/78 were selective in one or both tasks by the same criterion.
These results indicate that IT neurons may be contributing more than just a faithful representation of the sensory input in the act of visual recognition. Additionally, task-context dependent information does not appear to be correlated with the selectivity for complex stimuli often observed in the responses of IT neurons.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published0Classification versus identification: task context effects the responses of neurons in inferior temporal cortex150171542110677NKLogothetisJPaulsAOeltermannMAugathTTrinathSan Diego, CA, USA2001-11-00We describe a new method that combines microstimulation with fMRI for the detailed study of neural connectivity in the alive animal. We used specially constructed microelectrodes to stimulate directly a selected subcortical or cortical area while simultaneously measuring changes in brain activity, indexed by the blood oxygen level dependent (BOLD) signal. The exact location of the stimulation site was achieved by means of anatomical scans as well as by the study of the physiological properties of neurons. Imaging was carried out in a Biospec 4.7T/40 cm vertical bore scanner (Bruker, Inc), using pulse sequences described elsewhere (Logothetis et. al. Nature Neuroscience 1999). Electrical stimulation was delivered using a biphasic pulse generator attached to a constant-current stimulus isolation unit. Constant-current charge-balanced biphasic pulses (300usec, 50 to 150 uA, at 50 to 500 Hz) were delivered to the brain for 12.5 sec preceded and followed by 12.5 and 39 sec respectively. The compensation circuit, designed to minimize interference generated by the switching gradients during recording, was always active alleviating all gradient-induced currents in the range of the stimulation current. Local microstimulation of striate cortex yielded both local BOLD signals and activation of areas V2, V3, and MT. Microstimulation of dLGN resulted in the activation of striate cortex, as well as areas V2, V3, and MT. Our findings show that microstimulation combined with fMRI can be exquisitely used to find and study target areas of regions of electrophysiological interest.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published0In vivo study of connectivity with electrical microstimulation and fMRI150171542110667KSSaleemBAPrauseJPaulsMAugathTTrinathTHashikawaNKLogothetisSan Diego, CA, USA2001-11-00To date neuroanatomical connections have been mainly examined by means of degeneration methods and tracing techniques. Such studies require fixed processed tissue for the data analysis, and therefore they cannot be applied on the live animal. In the present study, we examined the neuronal connections in-vivo, particularly the output connections of striatum using MRI visible contrast agent (MnCl2) that is transported anterogradely through the axon, and subsequently trans-synaptically. MnCl2 (0.8 M) was injected into the caudate nucleus, and putamen in two rhesus monkeys. After the injection, the axonal transport of MnCl2 was continuously monitored for 24 hr or 45 hr using a 4.7T Biospec (Bruker, Inc) NMR scanner. We found a clear signal enhancement in the external and internal segments of the globus pallidus (Gpe and Gpi, respectively), and the substantia nigra, 24h after MnCl2 injection into the head of the caudate nucleus or putamen. Consistent with the previous anatomical studies, the spatial distribution of MnCl2 signal in globus pallidus, was different between caudate and putamen injections, with the former resulting in tracer accumulation in the dorsomedial, and the latter in the ventrolateral portion of the Gpe and Gpi. These findings were also confirmed histologically after WGA-HRP injection into the same region of the caudate or putamen, where the MnCl2 was injected. In addition, we found a strong signal increase in the thalamus and the cortical areas, particularly prefrontal and ventral inferotemporal areas, 45h after striatal injection. In conclusion, the tracer can be used to visualize neural networks with MRI.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published0Magnetic resonance imaging of neuronal connections in the macaque monkey150171542110607IBondarDLeopoldJPaulsNKLogothetisSan Diego, CA, USA2001-11-00The fast and accurate recognition of face identity is one of the hallmarks of primate visual performance. While numerous studies have revealed face-responsive neurons throughout the monkey brain, particularly in the superior temporal sulcus (STS) and inferotemporal (IT) lobe, the basic encoding strategies for faces remain poorly understood. Recent results using high-level adaptational aftereffects have suggested that the perception of identity involves reference to a stored prototype representation (Leopold et al., Nat. Neuro., 4:1, 2001). In the current study, we investigated the neurophysiological mechanisms underlying face perception in monkeys. We taught a monkey to discriminate between four human faces, and to indicate which face it perceived by pressing one of four buttons. We then measured the responses of IT and STS neurons to morphed faces that were modulated in their identity strength, as determined by their position in a computationally derived face-space. The monkey thus classified caricatures, anti-caricatures and anti-faces as one of the learned faces. Recordings were carried out with an implanted bundle of 64 high impedance Ni-Cr-Al microwire electrodes (Bondar & Logothetis, Soc. Neurosci. Abstr., 2000). Individual electrodes were different lengths, and the position of the bundle was adjustable in all directions, allowing for simultaneous measurement of single and multiple units, as well as local field potentials, from various areas in the temporal lobe. We will report on the modulation of temporal neurons to faces morphed along perceptually meaningful trajectories in face space.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published0Neural responses related to face identity in inferotemporal cortex of monkeys measured with 64 implanted electrodes150171542110477JPaulsNKLogothetisNew Orleans, LA, USA2000-11-00The contribution of temporal cortex (TE) to vision has been studied extensively in both human and nonhuman primates. Experiments in both species have focused on the consistency of neuronal responses to stimuli presented in a particular context in defining a functional role for TE in vision, however, the role of TE in cognition remains unknown. Do cells in TE respond differently to the same visual stimulus depending on the context in which it must be evaluated, or does their response remain the same, faithfully representing the sensory input? In order to address this question, we taught two monkeys (macaca mulatta) to perform a classification (CL) / identification (ID) task. Each trial began with the presentation of a colored frame, indicating the task the animal was to perform (blue - CL, orange - ID), followed by the presentation of a stimulus from one of a number of object classes (spheroids, wires, faces, monkeys, cars, greebles). The animal indicated its response by pressing one of 18 buttons. In the CL task, the animals were taught to group similar stimuli together by pressing one of 9 buttons located in front of their left hand for every member belonging to a class (e.g., button 1 for all faces), while, in the ID task, the animals had to use their right hand to indicate which of nine individuals from a given class had been presented. The learning of new classes of stimuli, as well as new individuals, was accompanied by an increase in reaction time and error rate that improved with training until performance for the two tasks was not significantly different. In currently ongoing, combined psychophysical-physiological experiments, the responses of single neurons in both medial and lateral aspects of TE are being evaluated with respect to task context.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published0Classification versus identification: a novel task for studying context effects in recognition150171542110507NKLogothetisJPaulsAOeltermannMAugathTTrinathNew Orleans, LA, USA2000-11-00The contribution of fMRI to our understanding of the functional anatomy of the brain is directly related to the degree to which the relationship between the MRI signal and the underlying neural activity is understood. It is established that activity in the brain is characterized by time-varying spatial distributions of action potentials superimposed on relatively slow-varying field potentials. To study how such potentials relate to the BOLD signal we scanned the visual cortex of anesthetized monkeys in a 4.7T scanner while recording local field potentials (LFPs), single (SUA), and multi (MUA) unit activity, by means of a novel, recently-developed recording technique. The geometry of novel electrodes and the active compensation built into the recording system minimized magnetic and electrostatic coupling respectively, permitting the elimination of any interference in subsequent off-line analysis. In each session, active sites were selected by first imaging the entire brain with a multi-shot, multi-slice gradient-recalled EPI MRI sequence (TE=20ms, TR=750ms), with FOV=128x128mm^2,128^2 matrix, 2mm thickness. Single slices, with areas of interest, were subsequently imaged with quadrature, transmit/receive volume or implanted surface coils with a voxel size of 250x250x660um^3 using time-resolved MR imaging (TE=20ms, TR=250ms). Our results provide insights into (a) the relationship of slow waves, single unit activity, and coherence functions of simultaneously-recorded single-units to the BOLD signal; (b) the temporal response function of the signals, and (c) the effects of anesthesia depth and stimulus strength on the modulation of each signal-type.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published0The relationship of LFPs, MUA, and SUA to the bold fMRI signal150171542110367NKLogothetisHGuggenbergerJPaulsMiami Beach, FL, USA1999-10-00313.7nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published-313.7Electrophysiological investigation of the BOLD signal15017154213067NKLogothetisHGuggenbergerJPaulsFort Lauderdale, FL, USA1999-05-00818nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published-818Precision and resolution of the fMRI signal in monkeys150171542110037NKLogothetisSPeledJPaulsLos Angeles, CA, USA1998-11-0011nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published-11Development and Application of fMRI for Visual Studies in Monkeys1501715421PaulsL19987JPaulsNKLogothetisTübingen, Germany1998-02-00104The inferior temporal cortex (IT) of the monkey has long been known to play an essential role in visual object recognition. The present study examines the role of IT neurons in combined psychophysical and electrophysiological experiments, in which monkeys learned to classify and recognize computer generated three-dimensional objects.
The monkeys recognized as the target only those 2-D views that were close to the familiar, training view (Logothetis et al., Current Biology, 1994). Recognition became increasingly difficult for them as the stimulus was rotated away from the experienced viewpoint, and they failed to recognize views farther than about ± 40 deg from the training view.
When the animals were trained with as few as three views of an object, 120 deg apart, they could often recognize all views resulting from rotations around the same axis. Such
performance suggests that view-invariant recognition of familiar objects by both humans and nonhuman primates involves perceptual learning and may be accomplished by a
viewer-centered system that interpolates between only a small number of stored views.
A population of IT neurons was found that responded selectively to views of recently learned objects (Logothetis et al, Current Biology, 1995). The cells discharged maximally for one object-view, and their response fell off gradually as the object was rotated away
from the neuron's preferred view. A systematic analysis of the response of these neurons to various parts of the view revealed that most cells were responding to a complex configuration within the view. The response of some other cells to object parts was highly nonlinear indicating more configurational or “holistic” selectivity. No selective responses were ever encountered for views that the animal systematically failed to recognize. For a number of objects that were used extensively during the training of the animals, and for which behavioral performance was view-independent, multiple cells were found that were tuned around different views of the same object. A very small number of neurons were selective for all views of one particular object.
Our experiments show that recognition of three-dimensional novel objects is a function of the object's retinal projection. This finding supports the notion of viewer-centered object representations for the purpose of recognition. Our results are similar to those obtained under similar circumstances in humans (Rock et al., JEP: Gen., 1981; Bülthoff & Edelman, PNAS, 1992). Our results suggest that IT neurons can develop a complex receptive field organization as a consequence of extensive training in the discrimination and recognition of objects. None of these objects had any prior meaning for the animal,
nor did they resemble anything familiar in the monkey's environment. These findings support the idea that a population of neurons -- each tuned to a different object aspect, showing a certain degree of invariance to image transformations, and selective for complex object features -- may, as an assembly, encode at least some types of complex 3-D objects for which structural decomposition is not possible or meaningful.nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published-104Evidence for the Encoding of Complex Object Features in
Monkey Inferior Temporal Cortex15017154219947JPaulsNKLogothetisWashington, DC, USA1995-11-0019nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published-19Invariances in Object Representation in Monkey Inferior Temporal (IT) Cortex9917JPaulsNKLogothetisFort Lauderdale, FL, USA1995-05-00S1052nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published0Invariance to Image Transformations in Monkey Inferior Temporal (IT) Cortex9867JPaulsNKLogothetisHouston, TX, USA1994-00-00nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published0Neuronal Correlates of Visual Object Recognition in the Nonhuman Primate9847NKLogothetisJPaulsHHBülthoffTPoggioWashington, DC, USA1993-11-0027nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published-27Responses of Inferotemporal (IT) Neurons to Novel Wire-Objects in Monkeys Trained in an Object Recognition Task9837NKLogothetisJPaulsHHBülthoffTPoggioSarasota, FL, USA1993-05-001132nonotspecifiedhttp://www.kyb.tuebingen.mpg.de/published-1132Evidence for recognition based on interpolation among 2D views of objects in monkeysShmuelAOPL200410AShmuelMAugathAOeltermannJPaulsNKLogothetis240710AShmuelMAAugathAOeltermannJPaulsNKLogothetis