Dissociating representations of affect and motion in visual cortices

While a delicious dessert being presented to us may elicit strong feelings of happiness and excitement, the same treat falling slowly away can lead to sadness and disappointment. Our emotional response to the item depends on its visual motion direction. Despite this importance, it remains unclear whether (and how) cortical areas devoted to decoding motion direction represents or integrates emotion with perceived motion direction. Motion-selective visual area V5/MT+ sits, both functionally and anatomically, at the nexus of dorsal and ventral visual streams. These pathways, however, differ in how they are modulated by emotional cues. The current study was designed to disentangle how emotion and motion perception interact, as well as use emotion-dependent modulation of visual cortices to understand the relation of V5/MT+ to canonical processing streams. During functional magnetic resonance imaging (fMRI), approaching, receding, or static motion after-effects (MAEs) were induced on stationary positive, negative, and neutral stimuli. An independent localizer scan was conducted to identify the visual-motion area V5/MT+. Through univariate and multivariate analyses, we demonstrated that emotion representations in V5/MT+ share a more similar response profile to that observed in ventral visual than dorsal, visual structures. Specifically, V5/MT+ and ventral structures were sensitive to the emotional content of visual stimuli, whereas dorsal visual structures were not. Overall, this work highlights the critical role of V5/MT+ in the representation and processing of visually acquired emotional content. It further suggests a role for this region in utilizing affectively salient visual information to augment motion perception of biologically relevant stimuli.

Daily fluctuations in visual motion discriminability contribute to daily fluctuations in continuous visuomotor performance

In ball sports such as table tennis, in which a ball moving at high speed is hit, an athlete's brain needs to process the motion information of the ball, predict the arrival point, and form a motor command to direct the racket there. Therefore, day-to-day fluctuations in visuomotor performance may be ascribed to fluctuations in visual motion discriminability, but it is not clear how the two are related. To examine this point, university table tennis players performed a motion direction discrimination (MDD) task and continuous visuomotor (CVM) task over 10 days as an estimation of visual motion discriminability and visuomotor performance, respectively. In the MDD task, using a joystick, participants distinguished the direction of a global coherent motion of target dots moving in the same direction on a PC monitor from innumerable dots moving in random directions. In the CVM task, participants hit sequential targets moving fast from right to left on the PC monitor by operating the cursor on the left side of the monitor up and down using the prehensile force of their thumb and index finger. The scores in the MDD and CVM tasks fluctuated day by day and showed a significant and moderate correlation between the MDD task score for the visual field in which the participants captured the target in the CVM task and the CVM task score. This correlation was confirmed even with the target moving from left to right. The fluctuations in the onset latency and the endpoint position of the cursor movement approaching the target were correlated with those of the visual motion discriminability, suggesting the contribution of motion vision to the speed and accuracy of the visuomotor performance. Moreover, these relationships were prominent in veteran players. For table tennis athletes, especially experienced players, fluctuations in the visual motion discrimination performance in a visual field specific for capturing a ball may be responsible for the fluctuations in continuous visuomotor (striking) performance.

Visual Motion Coherence Responses in Human Visual Cortex

Random dot kinematograms (RDKs) have recently been used to train subjects with cortical scotomas to perform direction of motion discrimination, partially restoring visual motion perception. To study the recovery of visual perception, it is important to understand how visual areas in normal subjects and subjects with cortical scotomas respond to RDK stimuli. Studies in normal subjects have shown that blood oxygen level-dependent (BOLD) responses in human area hV5/MT+ increase monotonically with coherence, in general agreement with electrophysiology studies in primates. However, RDK responses in prior studies were obtained while the subject was performing fixation, not a motion discrimination condition. Furthermore, BOLD responses were gauged against a baseline condition of uniform illumination or static dots, potentially decreasing the specificity of responses for the spatial integration of local motion signals (motion coherence). Here, we revisit this question starting from a baseline RDK condition of no coherence, thereby isolating the component of BOLD response due specifically to the spatial integration of local motion signals. In agreement with prior studies, we found that responses in the area hV5/MT+ of healthy subjects were monotonically increasing when subjects fixated without performing a motion discrimination task. In contrast, when subjects were performing an RDK direction of motion discrimination task, responses in the area hV5/MT+ remained flat, changing minimally, if at all, as a function of motion coherence. A similar pattern of responses was seen in the area hV5/MT+ of subjects with dense cortical scotomas performing direction of motion discrimination for RDKs presented inside the scotoma. Passive RDK presentation within the scotoma elicited no significant hV5/MT+ responses. These observations shed further light on how visual cortex responses behave as a function of motion coherence, helping to prepare the ground for future studies using these methods to study visual system recovery after injury.

Motion Coherence and Luminance Contrast Interact in Driving Visual Gamma-Band Activity

Synchronized neuronal population activity in the gamma-frequency range (>30 Hz) correlates with the bottom-up drive of various visual features. It has been hypothesized that gamma-band synchronization enhances the gain of neuronal representations, yet evidence remains sparse. We tested a critical prediction of the gain hypothesis, which is that features that drive synchronized gamma-band activity interact super-linearly. To test this prediction, we employed whole-head magnetencephalography in human subjects and investigated if the strength of visual motion (motion coherence) and luminance contrast interact in driving gamma-band activity in visual cortex. We found that gamma-band activity (64-128 Hz) monotonically increased with coherence and contrast, while lower frequency activity (8-32 Hz) decreased with both features. Furthermore, as predicted for a gain mechanism, we found a multiplicative interaction between motion coherence and contrast in their joint drive of gamma-band activity. The lower frequency activity did not show such an interaction. Our findings provide evidence that gamma-band activity acts as a cortical gain mechanism that nonlinearly combines the bottom-up drive of different visual features.

A flexible readout mechanism of human sensory representations

Attention can both enhance and suppress cortical sensory representations. However, changing sensory representations can also be detrimental to behavior. Behavioral consequences can be avoided by flexibly changing sensory readout, while leaving the representations unchanged. Here, we asked human observers to attend to and report about either one of two features which control the visibility of motion while making concurrent measurements of cortical activity with BOLD imaging (fMRI). We extend a well-established linking model to account for the relationship between these measurements and find that changes in sensory representation during directed attention are insufficient to explain perceptual reports. Adding a flexible downstream readout is necessary to best explain our data. Such a model implies that observers should be able to recover information about ignored features, a prediction which we confirm behaviorally. Thus, flexible readout is a critical component of the cortical implementation of human adaptive behavior.

Fundamentals of the modern theory of the phenomenon of "pain" from the perspective of a systematic approach. Neurophysiological basis. Part 1: A brief presentation of key subcellular and cellular ctructural elements of the central nervous system

The phenomenon of “pain” is a psychophysiological phenomenon that is actualized in the mind of a person as a result of the systemic response of his body to certain external and internal stimuli. The heart of the corresponding mental processes is certain neurophysiological processes, which in turn are caused by a certain form of the systemic structural and functional organization of the central nervous system (CNS). Thus, the systemic structural and functional organization of the central nervous system of a person, determining the corresponding psychophysiological state in a specific time interval, determines its psycho-emotional states or reactions manifested by the pain phenomenon. The nervous system of the human body has a hierarchical structure and is a morphologically and functionally complete set of different, interconnected, nervous and structural formations. The basis of the structural formations of the nervous system is nervous tissue. It is a system of interconnected differentials of nerve cells, neuroglia and glial macrophages, providing specific functions of perception of stimulation, excitation, generation of nerve impulses and its transmission. The neuron and each of its compartments (spines, dendrites, catfish, axon) is an autonomous, plastic, active, structural formation with complex computational properties. One of them – dendrites – plays a key role in the integration and processing of information. Dendrites, due to their morphology, provide neurons with unique electrical and plastic properties and cause variations in their computational properties. The morphology of dendrites: 1) determines – a) the number and type of contacts that a particular neuron can form with other neurons; b) the complexity, diversity of its functions; c) its computational operations; 2) determines – a) variations in the computational properties of a neuron (variations of the discharges between bursts and regular forms of pulsation); b) back distribution of action potentials. Dendritic spines can form synaptic connection – one of the main factors for increasing the diversity of forms of synaptic connections of neurons. Their volume and shape can change over a short period of time, and they can rotate in space, appear and disappear by themselves. Spines play a key role in selectively changing the strength of synaptic connections during the memorization and learning process. Glial cells are active participants in diffuse transmission of nerve impulses in the brain. Astrocytes form a three-dimensional, functionally “syncytia-like” formation, inside of which there are neurons, thus causing their specific microenvironment. They and neurons are structurally and functionally interconnected, based on which their permanent interaction occurs. Oligodendrocytes provide conditions for the generation and transmission of nerve impulses along the processes of neurons and play a significant role in the processes of their excitation and inhibition. Microglial cells play an important role in the formation of the brain, especially in the formation and maintenance of synapses. Thus, the CNS should be considered as a single, functionally “syncytia-like”, structural entity. Because the three-dimensional distribution of dendritic branches in space is important for determining the type of information that goes to a neuron, it is necessary to consider the three-dimensionality of their structure when analyzing the implementation of their functions.

A quantitative framework for motion visibility in human cortex

Despite the central use of motion visibility to reveal the neural basis of perception, perceptual decision making, and sensory inference there exists no comprehensive quantitative framework establishing how motion visibility parameters modulate human cortical response. Random-dot motion stimuli can be made less visible by reducing image contrast or motion coherence, or by shortening the stimulus duration. Because each of these manipulations modulates the strength of sensory neural responses they have all been extensively used to reveal cognitive and other nonsensory phenomena such as the influence of priors, attention, and choice-history biases. However, each of these manipulations is thought to influence response in different ways across different cortical regions and a comprehensive study is required to interpret this literature. Here, human participants observed random-dot stimuli varying across a large range of contrast, coherence, and stimulus durations as we measured blood-oxygen-level dependent responses. We developed a framework for modeling these responses that quantifies their functional form and sensitivity across areas. Our framework demonstrates the sensitivity of all visual areas to each parameter, with early visual areas V1-V4 showing more parametric sensitivity to changes in contrast and V3A and the human middle temporal area to coherence. Our results suggest that while motion contrast, coherence, and duration share cortical representation, they are encoded with distinct functional forms and sensitivity. Thus, our quantitative framework serves as a reference for interpretation of the vast perceptual literature manipulating these parameters and shows that different manipulations of visibility will have different effects across human visual cortex and need to be interpreted accordingly. NEW & NOTEWORTHY Manipulations of motion visibility have served as a key tool for understanding the neural basis for visual perception. Here we measured human cortical response to changes in visibility across a comprehensive range of motion visibility parameters and modeled these with a quantitative framework. Our quantitative framework can be used as a reference for linking human cortical response to perception and underscores that different manipulations of motion visibility can have greatly different effects on cortical representation.

Connectivity Reveals Sources of Predictive Coding Signals in Early Visual Cortex During Processing of Visual Optic Flow

Superimposed on the visual feed-forward pathway, feedback connections convey higher level information to cortical areas lower in the hierarchy. A prominent framework for these connections is the theory of predictive coding where high-level areas send stimulus interpretations to lower level areas that compare them with sensory input. Along these lines, a growing body of neuroimaging studies shows that predictable stimuli lead to reduced blood oxygen level-dependent (BOLD) responses compared with matched nonpredictable counterparts, especially in early visual cortex (EVC) including areas V1-V3. The sources of these modulatory feedback signals are largely unknown. Here, we re-examined the robust finding of relative BOLD suppression in EVC evident during processing of coherent compared with random motion. Using functional connectivity analysis, we show an optic flow-dependent increase of functional connectivity between BOLD suppressed EVC and a network of visual motion areas including MST, V3A, V6, the cingulate sulcus visual area (CSv), and precuneus (Pc). Connectivity decreased between EVC and 2 areas known to encode heading direction: entorhinal cortex (EC) and retrosplenial cortex (RSC). Our results provide first evidence that BOLD suppression in EVC for predictable stimuli is indeed mediated by specific high-level areas, in accord with the theory of predictive coding.

A Direct Demonstration of Functional Differences between Subdivisions of Human V5/MT

Two subdivisions of human V5/MT+: one located posteriorly (MT/TO-1) and the other more anteriorly (MST/TO-2) were identified in human participants using functional magnetic resonance imaging on the basis of their representations of the ipsilateral versus contralateral visual field. These subdivisions were then targeted for disruption by the application of repetitive transcranial magnetic stimulation (rTMS). The rTMS was delivered to cortical areas while participants performed direction discrimination tasks involving 3 different types of moving stimuli defined by the translational, radial, or rotational motion of dot patterns. For translational motion, performance was significantly reduced relative to baseline when rTMS was applied to both MT/TO-1 and MST/TO-2. For radial motion, there was a differential effect between MT/TO-1 and MST/TO-2, with only disruption of the latter area affecting performance. The rTMS failed to reveal a complete dissociation between MT/TO-1 and MST/TO-2 in terms of their contribution to the perception of rotational motion. On the basis of these results, MT/TO-1 and MST/TO-2 appear to be functionally distinct subdivisions of hV5/MT+. While both areas appear to be implicated in the processing of translational motion, only the anterior region (MST/TO-2) makes a causal contribution to the perception of radial motion.

Increase in MST activity correlates with visual motion learning: A functional MRI study of perceptual learning

Repeated practice of a specific task can improve visual performance, but the neural mechanisms underlying this improvement in performance are not yet well understood. Here we trained healthy participants on a visual motion task daily for 5 days in one visual hemifield. Before and after training, we used functional magnetic resonance imaging (fMRI) to measure the change in neural activity. We also imaged a control group of participants on two occasions who did not receive any task training. While in the MRI scanner, all participants completed the motion task in the trained and untrained visual hemifields separately. Following training, participants improved their ability to discriminate motion direction in the trained hemifield and, to a lesser extent, in the untrained hemifield. The amount of task learning correlated positively with the change in activity in the medial superior temporal (MST) area. MST is the anterior portion of the human motion complex (hMT+). MST changes were localized to the hemisphere contralateral to the region of the visual field, where perceptual training was delivered. Visual areas V2 and V3a showed an increase in activity between the first and second scan in the training group, but this was not correlated with performance. The contralateral anterior hippocampus and bilateral dorsolateral prefrontal cortex (DLPFC) and frontal pole showed changes in neural activity that also correlated with the amount of task learning. These findings emphasize the importance of MST in perceptual learning of a visual motion task. Hum Brain Mapp 39:145–156, 2018. © 2017 Wiley Periodicals, Inc.

Representation of illusory and physical rotations in human MST: A cortical site for the pinna illusion

Visual illusions have fascinated mankind since antiquity, as they provide a unique window to explore the constructive nature of human perception. The Pinna illusion is a striking example of rotation perception in the absence of real physical motion. Upon approaching or receding from the Pinna-Brelstaff figure, the observer experiences vivid illusory counter rotation of the two rings in the figure. Although this phenomenon is well known as an example of integration from local cues to a global percept, the visual areas mediating the illusory rotary perception in the human brain have not yet been identified. In the current study we investigated which cortical area in the human brain initially mediates the Pinna illusion, using psychophysical tests and functional magnetic resonance imaging (fMRI) of visual cortices V1, V2, V3, V3A, V4, and hMT+ of the dorsal and ventral visual pathways. We found that both the Pinna-Brelstaff figure (illusory rotation) and a matched physical rotation control stimulus predominantly activated subarea MST in hMT+ with a similar response intensity. Our results thus provide neural evidence showing that illusory rotation is initiated in human MST rather than MT as if it were physical rotary motion. The findings imply that illusory rotation in the Pinna illusion is mediated by rotation-sensitive neurons that normally encode physical rotation in human MST, both of which may rely on a cascade of similar integrative processes from earlier visual areas. Hum Brain Mapp 37:2097-2113, 2016. © 2016 Wiley Periodicals, Inc.

Eye Movements as Indicators of Vestibular Dysfunction

Virtual reality technologies are in wide use in sport psychology. An advantage of this kind of technology is the possibility to assess sportspeople’s readiness to perform complex movements. This study is aimed at developing a method for the evaluation of vestibular function disturbances in young skaters. Such disturbances may occur while skaters are performing rotation movements. To achieve this goal, we induced a vection illusion, accompanied by virtual environment rotation in a CAVE virtual reality system. Vestibular disturbances were tested for two groups—professional skaters and people who had very little or no skating experience. The quantitative evaluation of vestibular dysfunction was based on eye movement characteristics, which were recorded in subjects experiencing a vection illusion.

Motion area V5/MT+ response to global motion in the absence of V1 resembles early visual cortex

Motion area V5/MT+ shows a variety of characteristic visual responses, often linked to perception, which are heavily influenced by its rich connectivity with the primary visual cortex (V1). This human motion area also receives a number of inputs from other visual regions, including direct subcortical connections and callosal connections with the contralateral hemisphere. Little is currently known about such alternative inputs to V5/MT+ and how they may drive and influence its activity. Using functional magnetic resonance imaging, the response of human V5/MT+ to increasing the proportion of coherent motion was measured in seven patients with unilateral V1 damage acquired during adulthood, and a group of healthy age-matched controls. When V1 was damaged, the typical V5/MT+ response to increasing coherence was lost. Rather, V5/MT+ in patients showed a negative trend with coherence that was similar to coherence-related activity in V1 of healthy control subjects. This shift to a response-pattern more typical of early visual cortex suggests that in the absence of V1, V5/MT+ activity may be shaped by similar direct subcortical input. This is likely to reflect intact residual pathways rather than a change in connectivity, and has important implications for blindsight function. It also confirms predictions that V1 is critically involved in normal V5/MT+ global motion processing, consistent with a convergent model of V1 input to V5/MT+. Historically, most attempts to model cortical visual responses do not consider the contribution of direct subcortical inputs that may bypass striate cortex, such as input to V5/MT+. We have shown that the signal change driven by these non-striate pathways can be measured, and suggest that models of the intact visual system may benefit from considering their contribution.

Electrical stimulation of the human homolog of the medial superior temporal area induces visual motion blindness

Despite tremendous advances in neuroscience research, it is still unclear how neuronal representations of sensory information give rise to the contents of our perception. One of the first and also the most compelling pieces of evidence for direct involvement of cortical signals in perception comes from electrical stimulation experiments addressing the middle temporal (MT) area and the medial superior temporal (MST) area: two neighboring extrastriate cortical areas of the monkey brain housing direction-sensitive neurons. Here we have combined fMRI with electrical stimulation in a patient undergoing awake brain surgery, to separately probe the functional significance of the human homologs, i.e., area hMT and hMST, on motion perception. Both the stimulation of hMT and hMST made it impossible for the patient to perceive the global visual motion of moving random dot patterns. Although visual motion blindness was predominantly observed in the contralateral visual field, stimulation of hMST also affected the ipsilateral hemifield. These results suggest that early visual cortex up to the stage of MT is not sufficient for the perception of global visual motion. Rather, visual motion information must be mediated to higher-tier cortical areas, including hMST, to gain access to conscious perception.

A brain-derived metric for preferred kinetic stimuli

We here address the question of whether there is any correlation between subjective preference for simple configurations within a specific visual domain such as motion and strength of activity in visual areas in which that domain is emphasized. We prepared several distinctive patterns of dots in motion with various characteristics and asked humans to rate them according to their preference, before and while scanning the activity in their brains with functional magnetic resonance imaging. For simplicity, we restricted ourselves to motion in the fronto-parallel plane. Moving patterns produced activity in areas V1, V2, the V3 complex (V3, V3A, V3B) and V5, but only in areas V5, V3A/B and parietal cortex did the preferred kinetic patterns produce stronger activity when compared with the non-preferred ones. In addition, preferred patterns produced activity within field A1 of medial orbito-frontal cortex (mOFC), which is not otherwise activated by kinetic stimuli. Hence, for these areas, stronger neural activity correlated with subjective preference. We conclude that configurations of kinetic stimuli that are subjectively preferred correlate with stronger activity within early visual areas and within mOFC. This opens up the possibility of more detailed studies to relate subjective preferences to strength of activity in early visual areas and to relate activity in them to areas whose activity correlates with the subjective experience of beauty.

Parallel motion signals to the medial and lateral motion areas V6 and MT+

MT+ and V6 are key motion areas of the dorsal visual stream in both macaque and human brains. In the present study, we combined electrophysiological and neuroimaging methods (including retinotopic brain mapping) to find the electrophysiological correlates of V6 and to define its temporal relationship with the activity observed in MT+. We also determined the spatio-temporal profile of the motion coherency effect on visual evoked potentials (VEPs), and localized its neural generators. We found that area V6 participates in the very early phase of the coherent motion processing and that its electroencephalographic activity is almost simultaneous with that of MT+. We also found a late second activity in V6 that we interpret as a re-entrant feedback from extrastriate visual areas (e.g. area V3A). Three main cortical sources were differently modulated by the motion coherence: while V6 and MT+ showed a preference for the coherent motion, area V3A preferred the random condition. The response timing of these cortical sources indicates that motion signals flow in parallel from the occipital pole to the medial and lateral motion areas V6 and MT+, suggesting the view of a differential functional role.

Processing of coherent visual motion in topographically organized visual areas in human cerebral cortex

Recent imaging studies in human subjects have demonstrated representations of global visual motion in medial parieto-occipital cortex (area V6) and posterior parietal cortex, the latter containing at least seven topographically organized areas along the intraparietal sulcus (IPS0-IPS5, SPL1). In this fMRI study we used topographic mapping procedures to delineate a total of 18 visual areas in human cerebral cortex and tested their responsiveness to coherent visual motion under conditions of controlled attention and fixation. Preferences for coherent visual motion as compared to motion noise as well as hemispheric asymmetries were assessed for contralateral, ipsilateral, and bilateral visual motion presentations. Except for areas V1-V4 and IPS3-5, all other areas showed stronger responses to coherent motion with the most significant activations found in V6, followed by MT/MST, V3A, IPS0-2 and SPL1. Hemispheric differences were negligible altogether suggesting that asymmetries in parietal cortex observed in cognitive tasks do not reflect differences in basic visual response properties. Interestingly, areas V6, MST, V3A, and areas along the intraparietal sulcus showed specific representations of coherent visual motion not only when presented in the hemifield primarily covered by the given visual representation but also when presented in the ipsilateral visual field. This finding suggests that coherent motion induces a switch in spatial representation in specialized motion areas from contralateral to full-field coding.

Visual motion responses in the posterior cingulate sulcus: a comparison to V5/MT and MST

Motion processing regions apart from V5+/MT+ are still relatively poorly understood. Here, we used functional magnetic resonance imaging to perform a detailed functional analysis of the recently described cingulate sulcus visual area (CSv) in the dorsal posterior cingulate cortex. We used distinct types of visual motion stimuli to compare CSv with V5/MT and MST, including a visual pursuit paradigm. Both V5/MT and MST preferred 3D flow over 2D planar motion, responded less yet substantially to random motion, had a strong preference for contralateral versus ipsilateral stimulation, and responded nearly equally to contralateral and to full-field stimuli. In contrast, CSv had a pronounced preference to 2D planar motion over 3D flow, did not respond to random motion, had a weak and nonsignificant lateralization that was significantly smaller than that of MST, and strongly preferred full-field over contralateral stimuli. In addition, CSv had a better capability to integrate eye movements with retinal motion compared with V5/MT and MST. CSv thus differs from V5+/MT+ by its unique preference to full-field, coherent, and planar motion cues. These results place CSv in a good position to process visual cues related to self-induced motion, in particular those associated to eye or lateral head movements.

Disruption of MT impairs motion processing

Functional magnetic resonance imaging (fMRI) studies have associated motion processing with cortical region MT+, which includes sub-region MT that preferentially processes motion in the contralateral visual field. Transcranial magnetic stimulation (TMS) has been used to temporarily disrupt MT+ which impaired motion perception, suggesting this region is necessary for motion processing. In the present study, we used fMRI guided TMS to disrupt MT and determine whether this sub-region is necessary for motion processing. On an individual participant basis, MT was localized in each hemisphere using motion related fMRI activity on the posterior bank of the ascending limb of the inferior temporal sulcus. In the first experiment, 1 Hz TMS of left MT preferentially impaired motion detection in the contralateral versus ipsilateral visual field. In the second experiment, single-pulse TMS of MT impaired motion processing to a greater degree than color processing. These results provide convergent evidence that sub-region MT is necessary for motion processing.

Beyond visual, aural and haptic movement perception: hMT+ is activated by electrotactile motion stimulation of the tongue in sighted and in congenitally blind individuals

The motion-sensitive middle temporal cortex (hMT+ complex) responds also to non-visual motion stimulation conveyed through the tactile and auditory modalities, both in sighted and in congenitally blind individuals. This indicates that hMT+ is truly responsive to motion-related information regardless of visual experience and the sensory modality through which such information is carried to the brain. Here we determined whether the hMT+ complex responds to motion perception per se, that is, motion not perceived through the visual, haptic or aural modalities. Using functional magnetic resonance imaging (fMRI), we investigated brain responses in eight congenitally blind and nine sighted volunteers who had been trained to use the tongue display unit (TDU), a sensory substitution device which converts visual information into electrotactile pulses delivered to the tongue, to resolve a tactile motion discrimination task. Stimuli consisted of either static dots, dots moving coherently or dots moving in random directions. Both groups learned the task at the same rate and activated the hMT+ complex during tactile motion discrimination, although at different anatomical locations. Furthermore, the congenitally blind subjects showed additional activations within the dorsal extrastriate cortical pathway. These results extend previous data in support of the supramodal functional organization of hMT+ complex by showing that this cortical area processes motion-related information per se, that is, motion stimuli that are not visual in nature and that are administered to body structures that, in humans, are not primarily devoted to movement perception or spatial location, such as the tongue. In line with previous studies, the differential activations between sighted and congenitally blind individuals indicate that lack of vision leads to functional rearrangements of these supramodal cortical areas.

Effect of TMS on oculomotor behavior but not perceptual stability during smooth pursuit eye movements

During smooth pursuit eye movements, we do not mistake the shift of the retinal image induced by the visual background for motion of the world around us but instead perceive a stable world. The goal of this study was to search for the neuronal substrates providing perceptual stability. To this end, pursuit eye movements across a background stimulus and perceptual stability were measured in the absence and presence, respectively, of transcranial magnetic stimulation (TMS) applied to 6 different brain regions, that is, primary visual cortex (V1), area MT+/V5, left and right temporoparietal junctions (TPJs), medial parieto-occipital cortex (POC), and the lateral cerebellum (LC). Stimulation of MT+/V5 and the cerebellum induced significant decreases in pursuit gain independent of background presentation, whereas stimulation of TPJ impaired the suppression of the optokinetic reflex induced by background stimulation. In contrast to changes in pursuit, only nonsignificant modifications in perceptual stability were observed. We conclude that MT+/V5, TPJ, and the LC contribute to pursuit eye movements and that TPJ supports the suppression of optokinesis. The lack of significant influences of TMS on perception suggests that motion perception invariance is not based on a localized but rather a highly distributed network featuring parallel processing.

Visual motion perception deficits due to cerebellar lesions are paralleled by specific changes in cerebro-cortical activity

Recent anatomical studies have revealed strong cerebellar projections into parietal and prefrontal cortex. These findings suggest that the cerebellum might not only play a functional role in motor control but also cognitive domains, an idea also supported by neuropsychological testing of patients with cerebellar lesions that has revealed specific deficits. The goal of the present study was to test whether or not cognitive impairments after cerebellar damage are resulting from changes in cerebro-cortical signal processing. The detection of global visual motion embedded in noise, a faculty compromised after cerebellar lesions, was chosen as a model system. Using magnetoencephalography, cortical responses were recorded in a group of patients with cerebellar lesions (n = 8) and controls (n = 13) who observed visual motion of varied coherence, i.e., motion strength, presented in the peripheral visual field during controlled stationary fixation. Corroborating earlier results, the patients showed a significant impairment in global motion discrimination despite normal fixation behavior. This deficit was paralleled by qualitative differences in responses recorded from parieto-temporal cortex, including a reduced responsiveness to coherent visual motion and a striking loss of bilateral representations of motion coherence. Moreover, the perceptual thresholds correlated with the cortical representation of motion strength on single subject basis. These results demonstrate that visual motion processing in cerebral cortex critically depends on an intact cerebellum and establish a correlation between cortical activity and impaired visual perception resulting from cerebellar damage.