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January 1999 - present
Publications
Publications (80)
Extrastriate visual area V5/MT in primates is defined both structurally by myeloarchitecture and functionally by distinct responses to visual motion. Myelination is directly identifiable from postmortem histology but also indirectly by image contrast with structural magnetic resonance imaging (sMRI). First, we compared the identification of V5/MT u...
In the primate visual cortex, neurons signal differences in the appearance of objects with high precision. However, not all activated neurons contribute directly to perception. We defined the perceptual pool in extrastriate visual area V5/MT for a stereo-motion task, based on trial-by-trial co-variation between perceptual decisions and neuronal fir...
Judgments about the perceptual appearance of visual objects require the combination of multiple parameters, like location, direction, color, speed, and depth. Our understanding of perceptual judgments has been greatly informed by studies of ambiguous figures, which take on different appearances depending upon the brain state of the observer. Here w...
Vision research has the potential to reveal fundamental mechanisms underlying sensory experience. Causal experimental approaches, such as electrical microstimulation, provide a unique opportunity to test the direct contributions of visual cortical neurons to perception and behaviour. But in spite of their importance, causal methods constitute a min...
Decision-making models distil principles of information processing that underlie a range of cognitive functions. For the cases of motion detection in random-dot kinematograms and decisions about the rotation of 3D structure-from-motion cylinders, contributing neural processes have been localized to specific circuits in extrastriate area V5/MT on th...
Primate lateral intraparietal area (LIP) is critical for cognitive processing. Its contribution to categorization and decision-making has been causally linked to neurons' spatial sensorimotor selectivity. We reveal the intrinsic anatomical circuits and neuronal responses within LIP that provide the substrate for this flexible generation of motor re...
Noninvasive diffusion-weighted magnetic resonance imaging (dMRI) can be used to map the neural connectivity between distinct areas in the intact brain, but the standard resolution achieved fundamentally limits the sensitivity of such maps. We investigated the sensitivity and specificity of high-resolution postmortem dMRI and probabilistic tractogra...
Behavioural context in the form of reward expectation or the social influence of conspecifics has profound effects on the decisions primates make. A central question is whether such contextual influences can already bias processing of sensory stimuli (and thereby affect perception), or whether they predominantly exert their effects by altering brai...
Diffusion-weighted magnetic resonance imaging (DW-MRI) tractography is a non-invasive tool to probe neural connections and the structure of the white matter. It has been applied successfully in studies of neurological disorders and normal connectivity. Recent work has revealed that tractography produces a high incidence of false-positive connection...
Spiking activity in single neurons of the primate visual cortex has been tightly linked to perceptual decisions. Any mechanism that reads out these perceptual signals to support behavior must respect the underlying neuroanatomy that shapes the functional properties of sensory neurons. Spatial distribution and timing of inputs to the next processing...
One of the most influential accounts of central orbitofrontal cortex—that it mediates behavioral flexibility—has been challenged by the finding that discrimination reversal in macaques, the classic test of behavioral flexibility, is unaffected when lesions are made by excitotoxin injection rather than aspiration. This suggests that the critical bra...
Evolutionary adaptations of temporo-parietal cortex are considered to be a critical specialization of the human brain. Cortical adaptations, however, can affect different aspects of brain architecture, including local expansion of the cortical sheet or changes in connectivity between cortical areas. We distinguish different types of changes in brai...
Evolutionary adaptations of temporo-parietal cortex are considered to be a critical specialization of the human brain. Cortical adaptations, however, can affect different aspects of brain architecture, including local expansion of the cortical sheet or changes in connectivity between cortical areas. We distinguish different types of changes in brai...
Evolutionary adaptations of temporo-parietal cortex are considered to be a critical specialization of the human brain. Cortical adaptations, however, can affect different aspects of brain architecture, including local expansion of the cortical sheet or changes in connectivity between cortical areas. We distinguish different types of changes in brai...
The frontal lobe is central to distinctive aspects of human cognition and behavior. Some comparative studies link this to a larger frontal cortex and even larger frontal white matter in humans compared with other primates, yet others dispute these findings. The discrepancies between studies could be explained by limitations of the methods used to q...
Evaluation of the structural connectivity (SC) of the brain based on tractography has mainly focused on the choice of diffusion model, tractography algorithm, and their respective parameter settings. Here, we systematically validate SC derived from a post mortem monkey brain, while varying key acquisition parameters such as the b-value, gradient an...
Recording from single neurons in the brain for long periods of time has been a central goal in both basic neuroscience and translational neurology, in order to understand mechanisms underlying brain processes such as learning and to understand the pathogenesis of neurodynamic disease states. Recent advances in materials engineering, digital signal...
Perceptual decisions are thought to depend on the activation of task-relevant neurons, whose activity is often correlated in time. Here, we examined how the temporal structure of shared variability in neuronal firing relates to perceptual choices. We recorded stimulus-selective neurons from visual area V5/MT while two monkeys (Macaca mulatta) made...
Lesions of primary visual cortex (V1) lead to loss of conscious visual perception with significant impact on human patients. Understanding the neural consequences of such damage may aid the development of rehabilitation methods. In this rare case of a Rhesus macaque (monkey S), likely born without V1, the animal’s in-group behaviour was unremarkabl...
Evolutionary adaptations can affect different aspects of brain architecture, including areal expansion, relocation, or changes in connectivity profiles. Distinguishing between different types of reorganization is critical for our understanding of brain evolution. We propose to address this using a computational neuroanatomy approach. We investigate...
One of the most influential accounts of central orbitofrontal cortex − that it mediates behavioral flexibility − has been challenged by the finding that discrimination reversal in macaques − the classic test of behavioral flexibility − is unaffected when lesions are made by excitotoxin injection rather than aspiration. This suggests the critical br...
To understand brain circuits it is necessary both to record and manipulate their activity. Transcranial ultrasound stimulation (TUS) is a promising non-invasive brain stimulation technique. To date, investigations report short-lived neuromodulatory effects, but to deliver on its full potential for research and therapy, ultrasound protocols are requ...
Significance
Social influence biases even simple perceptual decisions across a range of contexts. The development and mechanism of such biases remain unclear. We systematically examined the developmental course of social influence bias exerted by another person on perceptual decisions in children between 6 and 14 years old. To probe underlying mech...
Lesions of primate primary visual cortex (V1) lead to loss of conscious visual perception, and are often devastating to those affected. Understanding the neural consequences of such damage may aid the development of rehabilitation methods. In this rare case of a Rhesus macaque (monkey S), likely born without V1, we investigated the brain structures...
To understand brain circuits it is necessary both to record and manipulate their activity. Despite increased availability of techniques for manipulating neural activity in rodents, manipulating neural activity in primates remains difficult. Here we show that a minimally invasive technique, transcranial focused ultrasound stimulation (TUS), induced...
Zusammenfassung
Die neurowissenschaftliche Forschung hat enorme Fortschritte in der Entschlüsselung der neuronalen Codes unserer Sinneswahrnehmung erzielt. Von Einzelzellen in der Sehrinde des Affen bis zu Aktivitätsmustern in neuronalen Schaltkreisen korreliert elektrische Aktivität über verschiedene Ebenen mit Wahrnehmung. Der Schlüssel zum Verst...
Neuroscientific research has made tremendous progress towards unravelling the neuronal codes that underlie our rich sensory perception and experience. From single neurons in primates’ visual brain that predict perceptual choices to activity patterns in defined neuronal circuits, electrical activity across different levels correlates with perception...
The parietal lobe has a unique place in the human brain. Anatomically, it is at the crossroad between the frontal, occipital, and temporal lobes, thus providing a middle ground for multimodal sensory integration. Functionally, it supports higher cognitive functions that are characteristic of the human species, such as mathematical cognition, semant...
Autism spectrum disorder is a debilitating condition with possible neurodevelopmental origins but unknown neuroanatomical correlates. Whereas investigators have paid much attention to the cerebral cortex, few studies have detailed the basal ganglia in autism. The caudate nucleus may be involved in the repetitive movements and limbic changes of auti...
Human social life has changed dramatically in the past 100 years, as first advances in transport and later the Internet allowed us to interact with a much greater and more diverse group of people. As a result, even the term “social networks” has a profound new meaning in the 21st century. The human species is now more connected than ever, and we li...
Stereoscopic vision delivers a sense of depth based on binocular information but additionally acts as a mechanism for achieving correspondence between patterns arriving at the left and right eyes. We analyse quantitatively the cortical architecture for stereoscopic vision in two areas of macaque visual cortex. For primary visual cortex V1, the resu...
Large and small reward conditions do not differ in the proportion of microstimulated trials, nor in the distribution of stimulus disparities.
The nature of the reward contingencies in this experiment meant that the reward size for any particular trial was dictated by the monkey's accumulated performance on the previous trials. Therefore, the distri...
Causal methods to interrogate brain function have been employed since the advent of modern neuroscience in the nineteenth century. Initially, randomly placed electrodes and stimulation of parts of the living brain were used to localize specific functions to these areas. Recent technical developments have rejuvenated this approach by providing more...
Magnetoencephalography (MEG) allows the physiological recording of human brain activity at high temporal resolution. However, spatial localization of the source of the MEG signal is an ill-posed problem as the signal alone cannot constrain a unique solution and additional prior assumptions must be enforced. An adequate source reconstruction method...
Classic studies on social influence used simple perceptual decision-making tasks to examine how the opinions of others change individuals' judgments. Since then, one of the most fundamental questions in social psychology has been whether social influence can alter basic perceptual processes. To address this issue, we used a diffusion model analysis...
Illustration of the type of stimulus used in this study. Consistent with an orthographic projection of a three-dimensional cylinder, the peak velocity of the stimulus dots was at the midline of cylinder image; i.e., the dot velocity increased as they approached the midline and then decreased as they moved toward the lateral edges of the cylinder. T...
Visual area MT is a model of choice in primate neurophysiological and human imaging research of visual perception, due to its considerable sensitivity to moving stimuli and the strong direction selectivity of its neurons. While the location of MT(V5) in the non-human primate is easily identifiable based on gross anatomy and appears consistent betwe...
A large fraction of the primate brain, especially of the cortex, is dedicated to the processing of visual information. A complex network of brain structures transforms electrical signals in the eye about local differences in brightness into signals which directly relate to visual perception in higher areas of visual cortex. Using electrical recordi...
Judgments of visual depth rely crucially on the relative binocular disparity between two visual features. While areas of ventral visual cortex contain neurons that signal the relative disparity between spatially adjacent visual features, the same tests in dorsal visual areas yield little evidence for relative disparity selectivity. We investigated...
Visual area V5/MT in the rhesus macaque has a distinct functional organization, where neurons with specific preferences for direction of motion and binocular disparity are co-organized in columns or clusters. Here, we analyze the pattern of intrinsic connectivity within cortical area V5/MT in both parasagittal sections of the intact brain and tange...
Variations in firing of single neurons in MT(V5) of awake, behaving macaques correlate highly with perceptual choice for the rotation of an ambiguous zero disparity cylinder (choice probability 0.67). Neuronal responses in MT(V5) are also correlated with direction discrimination in a random motion stimulus, but this choice probability is considerab...
In the awake macaque, MT neuronal firing to ambiguously rotating cylinders is correlated with the reported direction of rotation when the stimulus is closely matched to the neuronal receptive field. We recently reported the existence of strong choice-related firing in MT, even when the orientation of the cylinder is sub-optimal for the neuron (Curn...
Emerging evidence suggests that the long-established distinction between habit-based and goal-directed decision-making mechanisms can also be sustained in humans. Although the habit-based system has been extensively studied in humans, the goal-directed system is less well characterized. This review brings to that task the distinction between concep...
Making decisions is an integral part of everyday life. Social psychologists have demonstrated in many studies that humans' decisions are frequently and strongly influenced by the opinions of others--even in simple perceptual decisions, where, for example, participants have to judge what an image looks like. However, because the effect of other peop...
Comparison of performance on anaglyph stereo display and Wheatstone stereo display
Comparison of fitting parameters for gamma and gamma-rate fits
The included movie illustrates the general type of ambiguous stimulus used for these experiments. The attached movie does not replicate all aspects of the stimulus used in the experiments. In particular, the lifetime of the dots as viewed in a movie loop is infinite, whereas for the stimuli used in the experiments, individual dots in the display ha...
The cumulative distribution function (CDF) for participants with good performance (catch events correct≥75%)
The two experimental set-ups
Slowing of the rate at which a rivalrous percept switches from one configuration to another has been suggested as a potential trait marker for bipolar disorder. We measured perceptual alternations for a bistable, rotating, structure-from-motion cylinder in bipolar and control participants. In a control task, binocular depth rendered the direction o...
Neurons in the extrastriate visual area V5/MT show perceptually relevant signals in binocular depth tasks, which can be measured as a choice probability (CP) for the neuron. The presence of a CP in a particular paradigm may be an indicator that the neuron is generally part of the substrate for the perception of binocular depth. We compared the resp...
In the past two decades, sensory neuroscience has moved from describing response properties to external stimuli in cerebral cortex to establishing connections between neuronal activity and sensory perception. The seminal studies by Newsome, Movshon and colleagues in the awake behaving macaque firmly link single cells in extrastriate area V5/MT and...
Ambiguous figures that may take on the appearance of two or more distinct forms have fascinated philosophers and psychologists for generations. Recently, several laboratories have studied the neuronal basis of perceptual appearance at the level of single neurons in the cerebral cortex. Experiments that integrate neuronal recording with analyses bas...
BLDSC reference no.: D226393. Supervisors: Andrew Parker and Kristine Krug. Thesis (D.Phil.) - University of Oxford, 2003. Includes bibliographical references.
In order to isolate the neuronal activity that relates to the making of perceptual decisions, we have made use of a perceptually ambiguous motion stimulus. This stimulus lies on the boundary between two perceptual categories that correspond to clockwise and counter-clockwise rotation of a three-dimensional figure. It consists of a two-dimensional p...
In order to isolate the neuronal activity that relates to the making of perceptual decisions, we have made use of a perceptually ambiguous motion stimulus. This stimulus lies on the boundary between two perceptual categories that correspond to clockwise and counter-clockwise rotation of a three-dimensional figure. It consists of a two-dimensional p...
The role of the primate middle temporal area (MT) in depth perception was examined by considering the trial-to-trial correlations between neuronal activity and reported depth sensations. A set of moving random dots portrayed a cylinder rotating about its principal axis. In this structure-from-motion stimulus, the direction of rotation is ambiguous...
The role of the primate middle temporal area (MT) in depth perception was examined by considering the trial-to-trial correlations between neuronal activity and reported depth sensations. A set of moving random dots portrayed a cylinder rotating about its principal axis. In this structure-from-motion stimulus, the direction of rotation is ambiguous...
In studies of the developing mammalian visual system, it has been axiomatic that visual experience begins with eye-opening. Any role for neuronal activity earlier in development has been attributed to the patterned spontaneous activity found in retina and lateral geniculate nucleus (LGN). Here we show that, as early as 2 wk before eye-opening, visu...
In studies of the developing mammalian visual system, it has been axiomatic that visual experience begins with eye-opening. Any role for neuronal activity earlier in development has been attributed to the patterned spontaneous activity found in retina and lateral geniculate nucleus (LGN). Here we show that, as early as 2 wk before eye-opening, visu...
We have examined the spatial-frequency selectivity of neurons in areas 17 and 18 of the adult pigmented ferret, by measuring how the amplitude of response depends on the spatial-frequency of moving sinusoidal gratings of optimal orientation and fixed contrast. Neurons in area 17 of the ferret respond optimally to low spatial frequencies [average 0....
Precise point-to-point connectivity is the basis of ordered maps of the visual field. The immaturity of the newborn hamster's visual system has allowed us to examine emerging topography in the geniculo-cortical projection well before thalamic axons have reached their cortical target, layer IV. Using anterograde transneuronal labeling with wheat ger...
