Extrastriate Areas Research Articles

Brain Activity in Response to Visual Symmetry

A number of studies have explored visual symmetry processing by measuring event related potentials and neural oscillatory activity. There is a sustained posterior negativity (SPN) related to the presence of symmetry. There is also functional magnetic resonance imaging (MRI) activity in extrastriate visual areas and in the lateral occipital complex. We summarise the evidence by answering six questions. (1) Is there an automatic and sustained response to symmetry in visual areas? Answer: Yes, and this suggests automatic processing of symmetry. (2) Which brain areas are involved in symmetry perception? Answer: There is an extended network from extrastriate areas to higher areas. (3) Is reflection special? Answer: Reflection is the optimal stimulus for a more general regularity-sensitive network. (4) Is the response to symmetry independent of view angle? Answer: When people classify patterns as symmetrical or random, the response to symmetry is view-invariant. When people attend to other dimensions, the network responds to residual regularity in the image. (5) How are brain rhythms in the two hemispheres altered during symmetry perception? Answer: Symmetry processing (rather than presence) produces more alpha desynchronization in the right posterior regions. Finally, (6) does symmetry processing produce positive affect? Answer: Not in the strongest sense, but behavioural measures reveal implicit positive evaluation of abstract symmetry.

Relationship of high blood lactate levels with latency of visual-evoked potentials.

We studied, in healthy adult subjects, the association of high blood lactate levels, induced with an exhaustive exercise (12 subjects) or an intravenous infusion (four subjects) of a lactate solution (3 mg/kg in 1 min), with amplitude and latency of visual-evoked potentials. Amplitude of N75, P100, and N145 components did not show significant changes, whereas latency of P100 was reduced at exercise's end and that of N145 increased 10 min after the conclusion. Therefore, an increase of blood lactate induced by an exhaustive exercise or an intravenous infusion appears to induce an improvement in the conduction time between eye and striate cortex, while it seems to evoke a worsening of intracortical communication between striate and extrastriate areas.

Body-selective areas in the visual cortex are less active in children than in adults.

Our ability to read other people’s non-verbal signals gets refined throughout childhood and adolescence. How this is paralleled by brain development has been investigated mainly with regards to face perception, showing a protracted functional development of the face-selective visual cortical areas. In view of the importance of whole-body expressions in interpersonal communication it is important to understand the development of brain areas sensitive to these social signals. Here we used functional magnetic resonance imaging (fMRI) to compare brain activity in a group of 24 children (age 6–11) and 26 adults while they passively watched short videos of body or object movements. We observed activity in similar regions in both groups; namely the extra-striate body area (EBA), fusiform body area (FBA), posterior superior temporal sulcus (pSTS), amygdala and premotor regions. Adults showed additional activity in the inferior frontal gyrus (IFG). Within the main body-selective regions (EBA, FBA and pSTS), the strength and spatial extent of fMRI signal change was larger in adults than in children. Multivariate Bayesian (MVB) analysis showed that the spatial pattern of neural representation within those regions did not change over age. Our results indicate, for the first time, that body perception, like face perception, is still maturing through the second decade of life.

Contextual modulation and stimulus selectivity in extrastriate cortex.

Contextual modulation is observed throughout the visual system, using techniques ranging from single-neuron recordings to behavioral experiments. Its role in generating feature selectivity within the retina and primary visual cortex has been extensively described in the literature. Here, we describe how similar computations can also elaborate feature selectivity in the extrastriate areas of both the dorsal and ventral streams of the primate visual system. We discuss recent work that makes use of normalization models to test specific roles for contextual modulation in visual cortex function. We suggest that contextual modulation renders neuronal populations more selective for naturalistic stimuli. Specifically, we discuss contextual modulation's role in processing optic flow in areas MT and MST and for representing naturally occurring curvature and contours in areas V4 and IT. We also describe how the circuitry that supports contextual modulation is robust to variations in overall input levels. Finally, we describe how this theory relates to other hypothesized roles for contextual modulation.

Why is "blindsight" blind? A new perspective on primary visual cortex, recurrent activity and visual awareness.

The neuropsychological phenomenon of blindsight has been taken to suggest that the primary visual cortex (V1) plays a unique role in visual awareness, and that extrastriate activation needs to be fed back to V1 in order for the content of that activation to be consciously perceived. The aim of this review is to evaluate this theoretical framework and to revisit its key tenets. Firstly, is blindsight truly a dissociation of awareness and visual detection? Secondly, is there sufficient evidence to rule out the possibility that the loss of awareness resulting from a V1 lesion simply reflects reduced extrastriate responsiveness, rather than a unique role of V1 in conscious experience? Evaluation of these arguments and the empirical evidence leads to the conclusion that the loss of phenomenal awareness in blindsight may not be due to feedback activity in V1 being the hallmark awareness. On the basis of existing literature, an alternative explanation of blindsight is proposed. In this view, visual awareness is a "global" cognitive function as its hallmark is the availability of information to a large number of perceptual and cognitive systems; this requires inter-areal long-range synchronous oscillatory activity. For these oscillations to arise, a specific temporal profile of neuronal activity is required, which is established through recurrent feedback activity involving V1 and the extrastriate cortex. When V1 is lesioned, the loss of recurrent activity prevents inter-areal networks on the basis of oscillatory activity. However, as limited amount of input can reach extrastriate cortex and some extrastriate neuronal selectivity is preserved, computations involving comparison of neural firing rates within a cortical area remain possible. This enables "local" read-out from specific brain regions, allowing for the detection and discrimination of basic visual attributes. Thus blindsight is blind due to lack of "global" long-range synchrony, and it functions via "local" neural readout from extrastriate areas.

Robust expertise effects in right FFA

The fusiform face area (FFA) is one of several areas in occipito-temporal cortex whose activity is correlated with perceptual expertise for objects. Here, we investigate the robustness of expertise effects in FFA and other areas to a strong task manipulation that increases both perceptual and attentional demands. With high-resolution fMRI at 7T, we measured responses to images of cars, faces and a category globally visually similar to cars (sofas) in 26 subjects who varied in expertise with cars, in (a) a low load 1-back task with a single object category and (b) a high load task in which objects from two categories were rapidly alternated and attention was required to both categories. The low load condition revealed several areas more active as a function of expertise, including both posterior and anterior portions of FFA bilaterally (FFA1/FFA2, respectively). Under high load, fewer areas were positively correlated with expertise and several areas were even negatively correlated, but the expertise effect in face-selective voxels in the anterior portion of FFA (FFA2) remained robust. Finally, we found that behavioral car expertise also predicted increased responses to sofa images but no behavioral advantages in sofa discrimination, suggesting that global shape similarity to a category of expertise is enough to elicit a response in FFA and other areas sensitive to experience, even when the category itself is not of special interest. The robustness of expertise effects in right FFA2 and the expertise effects driven by visual similarity both argue against attention being the sole determinant of expertise effects in extrastriate areas.

Beta oscillation dynamics in extrastriate cortex after removal of primary visual cortex.

The local field potential (LFP) in visual cortex is typically characterized by the following spectral pattern: before the onset of a visual stimulus, low-frequency oscillations (beta, 12-20 Hz) dominate, whereas during the presentation of a stimulus these oscillations diminish and are replaced by fluctuations at higher frequencies (gamma, >30 Hz). The origin of beta oscillations in vivo remains unclear, as is the basis of their suppression during visual stimulation. Here we investigate the contribution of ascending input from primary visual cortex (V1) to beta oscillation dynamics in extrastriate visual area V4 of behaving monkeys. We recorded LFP activity in V4 before and after resecting a portion of V1. After the surgery, the visually induced gamma LFP activity in the lesion projection zone of V4 was markedly reduced, consistent with previously reported spiking responses (Schmid et al., 2013). In the beta LFP range, the lesion had minimal effect on the normal pattern of spontaneous oscillations. However, the lesion led to a surprising and permanent reversal of the normal beta suppression during visual stimulation, with visual stimuli eliciting beta magnitude increases up to 50%, particularly in response to moving stimuli. This reversed beta activity pattern was specific to stimulus locations affected by the V1 lesion. Our results shed light on the mechanisms of beta activity in extrastriate visual cortex: The preserved spontaneous oscillations point to a generation mechanism independent of the geniculostriate pathway, whereas the positive beta responses support the contribution of visual information to V4 via direct thalamo-extrastriate projections.

Can we simulate an action that we temporarily cannot perform?

The scope of individuals' motor repertoire and expertise influences the way they perceive the actions of others. When observing skilled actions, experts recruit the cortical network subserving action perception (action observation network, AON) to a greater extent than non-experts. However, it remains unknown whether and how a temporary motor injury affects activation within the AON. To investigate this issue, brain hemodynamic activity was recorded twice in thirteen national female gymnasts suffering from a lower extremity injury at the onset of the experiment. The gymnasts were scanned one month after the injury and were shown gymnastics routines they were able and temporarily unable to perform. Six months later, after complete recovery, they were scanned again and shown the same routines they were now able to practice. Results showed: first, that the level of activity within the inferior parietal lobule and MT/V5/EBA (extrastriate body area), areas constitutive of the AON, was independent of the gymnasts' physical condition. Second, when gymnasts were hurt (vs. when recovered), higher activity in the cerebellum was detected. The equal contribution of MT/V5/EBA and inferior parietal lobule during the observation of movements the gymnasts were able or unable to practice suggests respectively that physical provisional incapacity does not interfere with the perceptual processing of body shape and motion information, and that motor expertise may prevent the decay of sensorimotor representations. Higher activations in the cerebellum may suggest that this structure plays a role in dissociating perceived physically feasible movements from those that are provisionally unfeasible.

Reduced resting-state functional connectivity of the somatosensory cortex predicts psychopathological symptoms in women with bulimia nervosa.

Background: Alterations in the resting-state functional connectivity (rs-FC) of several brain networks have been demonstrated in eating disorders. However, very few studies are currently available on brain network dysfunctions in bulimia nervosa (BN). The somatosensory network is central in processing body-related stimuli and it may be altered in BN. The present study therefore aimed to investigate rs-FC in the somatosensory network in bulimic women.Methods: Sixteen medication-free women with BN (age = 23 ± 5 years) and 18 matched controls (age = 23 ± 3 years) underwent a functional magnetic resonance resting-state scan and assessment of eating disorder symptoms. Within-network and seed-based functional connectivity analyses were conducted to assess rs-FC within the somatosensory network and to other areas of the brain.Results: Bulimia nervosa patients showed a decreased rs-FC both within the somatosensory network (t = 9.0, df = 1, P = 0.005) and with posterior cingulate cortex and two visual areas (the right middle occipital gyrus and the right cuneus) (P = 0.05 corrected for multiple comparison). The rs-FC of the left paracentral lobule with the right middle occipital gyrus correlated with psychopathology measures like bulimia (r = −0.4; P = 0.02) and interoceptive awareness (r = −0.4; P = 0.01). Analyses were conducted using age, BMI (body mass index), and depressive symptoms as covariates.Conclusion: Our findings show a specific alteration of the rs-FC of the somatosensory cortex in BN patients, which correlates with eating disorder symptoms. The region in the right middle occipital gyrus is implicated in body processing and is known as extrastriate body area (EBA). The connectivity between the somatosensory cortex and the EBA might be related to dysfunctions in body image processing. The results should be considered preliminary due to the small sample size.

On the Role of Suppression in Spatial Attention: Evidence from Negative BOLD in Human Subcortical and Cortical Structures

There is clear evidence that spatial attention increases neural responses to attended stimuli in extrastriate visual areas and, to a lesser degree, in earlier visual areas. Other evidence shows that neurons representing unattended locations can also be suppressed. However, the extent to which enhancement and suppression is observed, their stimulus dependence, and the stages of the visual system at which they are expressed remains poorly understood. Using fMRI we set out to characterize both the task and stimulus dependence of neural responses in the lateral geniculate nucleus (LGN), primary visual cortex (V1), and visual motion area (V5) in humans to determine where suppressive and facilitatory effects of spatial attention are expressed. Subjects viewed a lateralized drifting grating stimulus, presented at multiple stimulus contrasts, and performed one of three tasks designed to alter the spatial location of their attention. In retinotopic representations of the stimulus location, we observed increasing attention-dependent facilitation and decreasing dependence on stimulus contrast moving up the visual hierarchy from the LGN to V5. However, in the representations of unattended locations of the LGN and V1, we observed suppression, which was not significantly dependent on the attended stimulus contrast. These suppressive effects were also found in the pulvinar, which has been frequently associated with attention. We provide evidence, therefore, for a spatially selective suppressive mechanism that acts at a subcortical level.

Attenuation of the contingency detection effect in the extrastriate body area in autism spectrum disorder

Detection of the contingency between one's own behavior and consequent social events is important for normal social development, and impaired contingency detection may be a cause of autism spectrum disorder (ASD). To depict the neural underpinnings of this contingency effect, 19 adults with ASD and 22 control participants underwent functional MRI while imitating another's actions and their actions being imitated by the other. As the extrastriate body area (EBA) receives efference copies of one's own movements, we predicted that the EBA would show an atypical response during contingency detection in ASD. We manipulated two factors: the congruency of the executed and observed actions, and the order of action execution and observation. Both groups showed the congruency effect in the bilateral EBA during imitation. When action preceded observation, the left EBA of the control group showed the congruency effect, representing the response to being imitated, indicating contingency detection. The ASD group showed a reduced contingency effect in the left EBA. These results indicate that the function of the EBA in the contingency detection is altered in ASD.

The brain network underlying the recognition of hand gestures in the blind: the supramodal role of the extrastriate body area.

The visual perception of others' body parts is critical for understanding and imitating their behavior. The visual cortex in humans includes the extrastriate body area (EBA), which is a large portion of the occipitotemporal cortex that is selectively responsive to visually perceived body parts. Previous neuroimaging studies showed that the EBA not only receives sensory inputs regarding others' body information but also receives kinesthetic feedback regarding one's own actions. This finding raised the possibility that the EBA could be formed via nonvisual sensory modalities. However, the effect of visual deprivation on the formation of the EBA has remained largely unknown. Here, we used fMRI to investigate the effect of vision loss on the development of the EBA. Blind and sighted human subjects performed equally well in a haptic-identification task involving three categories of objects (hand shapes, toy cars, and teapots). The superior part (i.e., the middle temporal gyrus and angular gyrus) of the EBA and the supramarginal gyrus showed greater sensitivity to recognized hand shapes than to inanimate objects, regardless of the sensory modality and visual experience. Unlike the superior part of the EBA, the sensitivity of the inferior part (i.e., the inferior temporal sulcus and middle occipital gyrus) depended on visual experience. However, this vision-dependent sensitivity explained minor individual differences in hand-recognition performance. These results indicate that nonvisual modalities drive the development of the cortical network underlying the recognition of hand gestures with a node in the visual cortex.

Distinct contributions of extrastriate body area and temporoparietal junction in perceiving one's own and others' body.

The right temporoparietal cortex plays a critical role in body representation. Here, we applied repetitive transcranial magnetic stimulation (rTMS) over right extrastriate body area (EBA) and temporoparietal junction (TPJ) to investigate their causative roles in perceptual representations of one's own and others' body. Healthy women adjusted size-distorted pictures of their own body or of the body of another person according to how they perceived the body (subjective task) or how others perceived it (intersubjective task). In keeping with previous reports, at baseline, we found an overall underestimation of body size. Crucially, EBA-rTMS increased the underestimation bias when participants adjusted the images according to how others perceived their own or the other woman's body, suggesting a specific role of EBA in allocentric body representations. Conversely, TPJ-rTMS increased the underestimation bias when participants adjusted the body of another person, either a familiar other or a close friend, in both subjective and intersubjective tasks, suggesting an involvement of TPJ in representing others' bodies. These effects were body-specific, since no TMS-induced modulation was observed when participants judged a familiar object. The results suggest that right EBA and TPJ play active and complementary roles in the complex interaction between the perceptions of one's own and other people's body.

Body form and body motion processing are dissociable in the visual pathways.

Body form and body motion processing are dissociable in the visual pathways.

Action Sentences Activate Sensory Motor Regions in the Brain Independently of Their Status of Reality

Some studies have reported that understanding concrete action-related words and sentences elicits activations of motor areas in the brain. The present fMRI study goes one step further by testing whether this is also the case for comprehension of nonfactual statements. Three linguistic structures were used (factuals, counterfactuals, and negations), referring either to actions or, as a control condition, to visual events. The results showed that action sentences elicited stronger activations than visual sentences in the SMA, extending to the primary motor area, as well as in regions generally associated with the planning and understanding of actions (left superior temporal gyrus, left and right supramarginal gyri). Also, we found stronger activations for action sentences than for visual sentences in the extrastriate body area, a region involved in the visual processing of human body movements. These action-related effects occurred not only in factuals but also in negations and counterfactuals, suggesting that brain regions involved in action understanding and planning are activated by default even when the actions are described as hypothetical or as not happening. Moreover, some of these regions overlapped with those activated during the observation of action videos, indicating that the act of understanding action language and that of observing real actions share neural networks. These results support the claim that embodied representations of linguistic meaning are important even in abstract linguistic contexts.

Proprioceptive drift in the rubber hand illusion is intensified following 1 Hz TMS of the left EBA.

The rubber hand illusion (RHI) is a paradigm used to induce an illusory feeling of owning a dummy hand through congruent multisensory stimulation. Thus, it can grant insights into how our brain represents our body as our own. Recent research has demonstrated an involvement of the extrastriate body area (EBA), an area of the brain that is typically implicated in the perception of non-face body parts, in illusory body ownership. In this experiment, we sought causal evidence for the involvement of the EBA in the RHI. Sixteen participants took part in a sham controlled, 1 Hz repetitive transcranial magnetic stimulation (rTMS) experiment. Participants received (RHI condition) or asynchronous (control) stroking and were asked to report the perceived location of their real hand, as well as the intensity and the temporal onset of experienced ownership of the dummy hand. Following rTMS of the left EBA, participants misjudged their real hand’s location significantly more toward the dummy hand during the RHI than after sham stimulation. This difference in “proprioceptive drift” provides the first causal evidence that the EBA is involved in the RHI and subsequently in body representation and further supports the view that the EBA is necessary for multimodal integration.

Spatiotemporal dynamics of early cortical gesture processing

Gesture processing has been consistently shown to be associated with activation of the inferior parietal lobe (IPL); however, little is known about the integration of IPL activation into the temporal dynamics of early sensory areas. Using a temporally graded repetition suppression paradigm, we examined the activation and time course of brain areas involved in hand gesture processing. We recorded event-related potentials in response to stimulus pairs of static hand images forming gestures of the popular rock–paper–scissors game and estimated their neuronal generators. We identified two main components associated with adaptive patterns related to stimulus repetition. The N190 component elicited at temporo-parietal sites adapted to repetitions of the same gesture and was associated with right-hemispheric extrastriate body area activation. A later component at parieto-occipital sites demonstrated temporally graded adaptation effects for all gestures with a left-hemispheric dominance. Source localization revealed concurrent activations of the right extrastriate body area, fusiform gyri bilaterally, and the left IPL at about 250ms. The adaptation pattern derived from the graded repetition suppression paradigm demonstrates the functional sensitivity of these sources to gesture processing. Given the literature on IPL contribution to imitation, action recognition, and action execution, IPL activation at about 250ms may represent the access into specific cognitive routes for gesture processing and may thus be involved in integrating sensory information from cortical body areas into subsequent visuo-motor transformation processes.

Abnormal response to photic stimulation in juvenile myoclonic epilepsy: an EEG-fMRI study.

Juvenile myoclonic epilepsy (JME) is a young-onset electroclinical syndrome, characterized by myoclonic, generalized tonic-clonic, and possibly typical absence seizures. Interictal electroencephalography (EEG) displays 3-6 Hz spike/polyspike and wave pattern. Photosensitivity is common. Our aim was to explore the blood oxygen level-dependent (BOLD) response evoked by a highly provocative photic stimulus in a cohort of people with JME compared to a group of nonphotosensitive healthy controls, and to investigate the hemodynamic phenomena seen in patients with photosensitive JME. We studied 13 JME patients and 18 healthy controls using EEG-functional magnetic resonance imaging (fMRI) performed during low luminance intermittent photic stimulation (IPS). The BOLD response to IPS was investigated both in JME and control groups. In photosensitive JME subjects, we also performed a dynamic evaluation of BOLD signal changes evoked by the photoparoxysmal response (PPR) in a time frame ranging from 10 s before the onset of the EEG paroxysm up until 10 s afterward. The IPS evoked a positive BOLD response in striate and extrastriate visual areas, which was less in JME patients than in controls. Moreover, people with JME had a reduced positive BOLD response in the frontoparietal areas and putamen but a stronger negative BOLD response in the primary sensorimotor cortex (SM1) and in cortical regions belonging to the default mode network (DMN). In JME, the dynamic evaluation of BOLD signal changes related to PPR revealed an early positive response in the putamen and SM1, followed by BOLD signal decrements in the putamen, caudate nuclei, thalami, and SM1. Our results confirm the hypothesis that people with JME might have an altered interaction between the motor circuit and other neuronal networks, with prominent involvement of basal ganglia circuitry. The PPR could be a final expression of pathogenic phenomena occurring in the striato-thalamocortical system, possibly a core feature of system epilepsy JME.

Global selection of saccadic target features by neurons in area v4.

Psychophysical and neurophysiological studies indicate that during the preparation of saccades, visual processing at the target location is facilitated automatically by the deployment of attention. It has been assumed that the neural mechanisms involved in presaccadic shifts of attention are purely spatial in nature. Saccade preparation modulates the visual responses of neurons within extrastriate area V4, where the responses to targets are enhanced and responses to nontargets are suppressed. We tested whether this effect also engages a nonspatial form of modulation. We measured the responses of area V4 neurons to oriented gratings in two monkeys (Macaca mulatta) making delayed saccades to targets distant from the neuronal receptive field (RF). We varied the orientation of both the RF stimulus and the saccadic target. We found that, in addition to the spatial modulation, saccade preparation involves a feature-dependent modulation of V4 neuronal responses. Specifically, we found that the suppression of area V4 responses to nontarget stimuli during the preparation of saccades depends on the features of the saccadic target. Presaccadic suppression was absent when the features of the saccadic target matched the features preferred by individual V4 neurons. This feature-dependent modulation occurred in the absence of any feature-attention task. We show that our observations are consistent with a computational framework in which feature-based effects automatically emerge from saccade-related feedback signals that are spatial in nature.

Developmental remodeling of corticocortical feedback circuits in ferret visual cortex

Visual cortical areas in the mammalian brain are linked through a system of interareal feedforward and feedback connections, which presumably underlie different visual functions. We characterized the refinement of feedback projections to primary visual cortex (V1) from multiple sources in juvenile ferrets ranging in age from 4-10 weeks postnatal. We studied whether the refinement of different aspects of feedback circuitry from multiple visual cortical areas proceeds at a similar rate in all areas. We injected the neuronal tracer cholera toxin B (CTb) into V1 and mapped the areal and laminar distribution of retrogradely labeled cells in extrastriate cortex. Around the time of eye opening at 4 weeks postnatal, the retinotopic arrangement of feedback appears essentially adult-like; however, suprasylvian cortex supplies the greatest proportion of feedback, whereas area 18 supplies the greatest proportion in the adult. The density of feedback cells and the ratio of supragranular/infragranular feedback contribution declined in this period at a similar rate in all cortical areas. We also found significant feedback to V1 from layer IV of all extrastriate areas. The regularity of cell spacing, the proportion of feedback arising from layer IV, and the tangential extent of feedback in each area all remained essentially unchanged during this period, except for the infragranular feedback source in area 18, which expanded. Thus, while much of the basic pattern of cortical feedback to V1 is present before eye opening, there is major synchronous reorganization after eye opening, suggesting a crucial role for visual experience in this remodeling process.