Visual Association Cortex Research Articles

Representations of naturalistic stimulus complexity in early and associative visual and auditory cortices

The complexity of sensory stimuli has an important role in perception and cognition. However, its neural representation is not well understood. Here, we characterize the representations of naturalistic visual and auditory stimulus complexity in early and associative visual and auditory cortices. This is realized by means of encoding and decoding analyses of two fMRI datasets in the visual and auditory modalities. Our results implicate most early and some associative sensory areas in representing the complexity of naturalistic sensory stimuli. For example, parahippocampal place area, which was previously shown to represent scene features, is shown to also represent scene complexity. Similarly, posterior regions of superior temporal gyrus and superior temporal sulcus, which were previously shown to represent syntactic (language) complexity, are shown to also represent music (auditory) complexity. Furthermore, our results suggest the existence of gradients in sensitivity to naturalistic sensory stimulus complexity in these areas.

Semantically Congruent Sounds Facilitate the Decoding of Degraded Images

Semantically congruent sounds can facilitate perception of visual objects in the human brain. However, the manner in which semantically congruent sounds affect cognitive processing for degraded visual stimuli remains unclear. We presented participants with naturalistic degraded images and semantically congruent sounds from different conceptual categories in three modalities: degraded visual only, auditory only, and auditory and degraded visual. Functional magnetic resonance imaging was performed to assess variations in brain-activation spatial patterns. In order to account for the facilitation of auditory modulation at different levels, four conceptual categories of stimuli were divided into coarse and fine groups. Conjunction analysis and multivariate pattern analysis were used to investigate integrative properties. Superadditive interactions were found in the visual association cortex and subadditive interactions were observed in the superior temporal sulcus/superior temporal gyrus (STS/STG). Our results demonstrate that the visual association cortex and STS/STG are involved in the integration of auditory and degraded visual information. In addition, the pattern classification results imply that semantically congruent sounds may facilitate identification of degraded images in both coarse and fine groups. Importantly, when naturalistic visual stimuli were further subdivided, facilitation through auditory modulation exhibited category selectivity.

"Occipital Tunnel" Sign on FDG PET for Differentiating Dementias.

PET using FDG is a critical tool for evaluation of dementias, with characteristic patterns of hypometabolism suggesting specific diagnoses. Hypometabolism in the occipital region is recognized as an important finding associated with dementia with Lewy bodies and posterior cortical atrophy. We describe here the novel "occipital tunnel" sign, which results from relative sparing of FDG uptake in the medial occipital (primary visual) cortex compared with more severe loss in the surrounding lateral occipital (visual association) cortex. This sign is useful for recognizing the occipital findings of dementia with Lewy bodies and posterior cortical atrophy, especially when viewing sagittal projections.

Cerebral Responses to Acupuncture at GV24 and Bilateral GB13 in Rat Models of Alzheimer's Disease.

Acupuncture has been widely used in China to treat neurological diseases including Alzheimer's disease (AD). However, its mechanism remains unclear. In the present study, eighty healthy Wistar rats were divided into a normal control group (n = 15) and premodel group (n = 65). Forty-five rats that met the criteria for the AD model were then randomly divided into the model group (MG), the nonacupoint group (NG), and the acupoint group (AG). All rats received positron emission tomography (PET) scanning, and the images were analyzed with Statistical Parametric Mapping 8.0. MG exhibited hypometabolism in the olfactory bulb, insular cortex, orbital cortex, prelimbic cortex, striatum, parietal association cortex, visual cortex, cingulate gyrus, and retrosplenial cortex. AG exhibited prominent and extensive hypermetabolism in the thalamus, hypothalamus, bed nucleus of the stria terminalis, cerebral peduncle, midbrain tegmentum, and pontine tegmentum compared to NG. These results demonstrated that acupuncturing at GV24 and bilateral GB13 acupoints may improve the learning and memory abilities of the AD rats, probably via altering cerebral glucose metabolism (CGM) in the hypothalamus, thalamus, and brain stem. The observed effects of acupuncture may be caused by regulating the distribution of certain kinds of neurotransmitters and enhancing synaptic plasticity.

The Role of Visual Association Cortex in Associative Memory Formation across Development

The Role of Visual Association Cortex in Associative Memory Formation across Development

Altered functional connectivity in blepharospasm/orofacial dystonia.

IntroductionBlepharospasm is characterized by involuntary eyelid spasms. It can be associated with perioral dystonia (Meige's syndrome or orofacial dystonia). We aimed at studying resting‐state functional brain connectivity in these patients and its potential modulation by therapeutic botulinum toxin injections.MethodsWe performed resting‐state functional MRI and a region of interest‐based analysis of functional connectivity in 13 patients with blepharospasm/Meige's syndrome in comparison to 13 healthy controls. Patients were studied before and 4 weeks after botulinum toxin treatment. Simultaneous facial electromyography was applied to control for involuntary facial movements.ResultsBefore botulinum toxin treatment, patients showed reduced functional connectivity between caudate and primary sensorimotor, somatosensory association and visual cortices as well as between putamen and parietal association cortex. Cerebellar areas displayed decreased functional connectivity to somatosensory and visual association cortices. On the cortical level, connectivity was reduced between the cingulate cortex and the primary sensorimotor/premotor and parietal association cortex, between premotor areas and the primary somatosensory cortices, and between the postcentral gyrus and temporoparietal, secondary somatosensory, cingular, and cerebellar regions. Botulinum toxin treatment modulated functional connectivity, especially between cerebellum and visual cortices.ConclusionsPatients with blepharospasm/Meige's syndrome show altered functional connectivity at rest in widespread brain regions including basal ganglia, cerebellar, primary/secondary sensorimotor, and visual areas. Functionally, this may reflect a predisposition for defective movement inhibition and sensorimotor integration. Botulinum toxin treatment could modulate brain connectivity in blepharospasm by altering visual and sensory input.

Right Brodmann area 18 predicts tremor arrest after Vim radiosurgery: a voxel-based morphometry study

Drug-resistant essential tremor (ET) can benefit from open standard stereotactic procedures, such as deep-brain stimulation or radiofrequency thalamotomy. Non-surgical candidates can be offered either high-focused ultrasound (HIFU) or radiosurgery (RS). All proceduresaim to target the same thalamic site, the ventro-intermediate nucleus (e.g., Vim). The mechanisms by which tremor stops after Vim RS or HIFU remain unknown. We used voxel-based morphometry (VBM) on pretherapeutic neuroimaging data and assessed which anatomical site would best correlate with tremor arrest 1year after Vim RS. Fifty-two patients (30 male, 22 female; mean age 71.6years, range 49-82) with right-sided ET benefited from left unilateral Vim RS in Marseille, France. Targeting was performed in a uniform manner, using 130Gy and a single 4-mm collimator. Neurological (pretherapeutic and 1year after) and neuroimaging (baseline) assessments were completed. Tremor score on the treated hand (TSTH) at 1year after Vim RS was included in a statistical parametric mapping analysis of variance (ANOVA) model as a continuous variable with pretherapeutic neuroimaging data. Pretherapeutic gray matter density (GMD) was furthercorrelated with TSTH improvement. No a priori hypothesis was used in the statistical model. The only statistically significant region was right Brodmann area (BA) 18 (visual association area V2, p=0.05, cluster size Kc=71). Higher baseline GMD correlated with better TSTH improvement at 1 year after Vim RS(Spearman's rank correlation coefficient=0.002). Routine baseline structural neuroimaging predicts TSTH improvement 1year after Vim RS. The relevant anatomical area is the right visual association cortex (BA 18, V2). The question whether visual areas should be included in the targeting remains open.

The Role of Visual Association Cortex in Associative Memory Formation across Development.

Associative learning underlies the formation of new episodic memories. Associative memory improves across development, and this age-related improvement is supported by the development of the hippocampus and pFC. Recent work, however, additionally suggests a role for visual association cortex in the formation of associative memories. This study investigated the role of category-preferential visual processing regions in associative memory across development using a paired associate learning task in a sample of 56 youths (age 6-19 years). Participants were asked to bind an emotional face with an object while undergoing fMRI scanning. Outside the scanner, participants completed a memory test. We first investigated age-related changes in neural recruitment and found linear age-related increases in activation in lateral occipital cortex and fusiform gyrus, which are involved in visual processing of objects and faces, respectively. Furthermore, greater activation in these visual processing regions was associated with better subsequent memory for pairs over and above the effect of age and of hippocampal and pFC activation on performance. Recruitment of these visual processing regions mediated the association between age and memory performance, over and above the effects of hippocampal activation. Taken together, these findings extend the existing literature to suggest that greater recruitment of category-preferential visual processing regions during encoding of associative memories is a neural mechanism explaining improved memory across development.

Structure-function correlations in Retinitis Pigmentosa patients with partially preserved vision: a voxel-based morphometry study

Retinitis Pigmentosa is a group of hereditary retinal dystrophy disorders associated with progressive peripheral visual field loss. The impact of this retinal loss in cortical gray matter volume has not been addressed before in Retinitis Pigmentosa patients with low vision. Voxel-based morphometry was applied to study whole brain gray matter volume changes in 27 Retinitis Pigmentosa patients with partially preserved vision and 38 age- and gender-matched normally sighted controls to determine whether peripheral visual loss can lead to changes in gray matter volume. We found significant reductions in gray matter volume that were restricted to the occipital cortex of patients. The anteromedial pattern of reduced gray matter volume in visual primary and association cortices was significantly correlated with the extent of the peripheral visual field deficit in this cohort. Moreover, this pattern was found to be associated with the extent of visual field loss. In summary, we found specific visual cortical gray matter loss in Retinitis Pigmentosa patients associated with their visual function profile. The spatial pattern of gray matter loss is consistent with disuse-driven neuronal atrophy which may have clinical implications for disease management, including prosthetic restoration strategies.

CORTICAL BLINDNESS AND ANTON SYNDROME IN POSTERIOR CORTICAL ATROPHY

The dementia disorder - Posterio Cortical Atrophy (PCA) is clinically characterized by progressive impairment in visuoperception and visuospatial function. The imaging studies (brain MRI and FDG-PET/CT) show outstanding cortical atrophy or hypometabolism of visual association cortices of occipital, temporal and parietal lobes. Though the underlying pathology includes Alzheimer's disease, corticobasal degeneration and Lewy-body dementia, Alzheimer's pathology has been reported in majority of PCA patients in medical literature. Among all visual symptoms of PCA, cortical blindness and Anton syndrome mostly devastate patients. In this report, the PCA patients with cortical blindness and Anton syndrome are studies in a dementia specialty clinic. The medical charts of patients, who had met the diagnostic criteria of PCA from July 2015 to December 2016, were reviewed. For this study, the patients with documented cortical blindness and Anton syndrome were recruited. The data of clinical evaluation, MMSE scores, brain MRI studies, neurological reports, FDG-PET/CT, Amyloid-PET/CT and neuropsychiatric profiles were analyzed. There were four PCA patients with cortical blindness and Anton syndrome (one woman; three men). The average age was 58. Compared with the PCA patients without cortical blindness and Anton syndrome, these four subjects displayed either worse cortical atrophy of brain MRI studies or severe hypometablism of the FDG-PET/CT study. However, the positive result of Amyloid PET/CT was the same in these four subjects as those patients without cortical atrophy and Anton syndrome. These four subjects presented frequent neuropsychiatric symptoms daily, including agitation and visual hallucinations. The progression of PCA often results in cortical blindness and Anton syndrome. The implication of this development is extensive neuron loss and breakdown of higher cortical visual system. Early intervention of the Alzheimer pathology could be the future hope to halt the progression of PCA.

A case of recurrent depressive disorder presenting with Alice in Wonderland syndrome: psychopathology and pre- and post-treatment FDG-PET findings

BackgroundAlice in Wonderland syndrome (AIWS) is a rare neuropsychiatric syndrome that typically manifests in distortion of extrapersonal visual image, altered perception of one’s body image, and a disturbed sense of the passage of distance and time. Several conditions have been reported to contribute to AIWS, although its biological basis is still unknown. Here, we present the first case demonstrating a clear concurrence of recurrent depressive disorder and AIWS. The clinical manifestations and pre- and post-treatment fluorodeoxyglucose positron-emission tomographic (FDG-PET) images provide insights into the psychopathological and biological basis of AIWS.Case presentationWe describe a 63-year-old Japanese male who developed two distinct episodes of major depression concurrent with AIWS. In addition to typical AIWS perceptual symptoms, he complained of losing the ability to intuitively grasp the seriousness of news and the value of money, which implies disturbance of high-order cognition related to estimating magnitude and worth. Both depression and AIWS remitted after treatment in each episode. Pre-treatment FDG-PET images showed significant hypometabolism in the frontal cortex and hypermetabolism in the occipital and parietal cortex. Post-treatment images showed improvement of these abnormalities.ConclusionsThe clinical co-occurrence of depressive episodes and presentation of AIWS can be interpreted to mean that they have certain functional disturbances in common. In view of incapacity, indifference, devitalization, altered perception of one’s body image, and disturbed sense of time and space, the features of AIWS analogous to those of psychotic depression imply a common psychopathological basis. These high-order brain dysfunctions are possibly associated with the metabolic abnormalities in visual and parietotemporal association cortices that we observed on the pre- and post-treatment FDG-PET images in this case, while the hypometabolism in the frontal cortex is probably associated with depressive symptoms.

Pyramidal Neurons Are Not Generalizable Building Blocks of Cortical Networks

A key challenge in cortical neuroscience is to gain a comprehensive understanding of how pyramidal neuron heterogeneity across different areas and species underlies the functional specialization of individual neurons, networks, and areas. Comparative studies have been important in this endeavor, providing data relevant to the question of which of the many inherent properties of individual pyramidal neurons are necessary and sufficient for species-specific network and areal function. In this mini review, the importance of pyramidal neuron structural properties for signaling are outlined, followed by a summary of our recent work comparing the structural features of mouse (C57/BL6 strain) and rhesus monkey layer 3 (L3) pyramidal neurons in primary visual and frontal association cortices and their implications for neuronal and areal function. Based on these and other published data, L3 pyramidal neurons plausibly might be considered broadly “generalizable” from one area to another in the mouse neocortex due to their many similarities, but major differences in the properties of these neurons in diverse areas in the rhesus monkey neocortex rules this out in the primate. Further, fundamental differences in the dendritic topology of mouse and rhesus monkey pyramidal neurons highlight the implausibility of straightforward scaling and/or extrapolation from mouse to primate neurons and cortical networks.

The spatiotemporal substrates of autobiographical recollection: Using event-related ICA to study cognitive networks in action

Higher cognitive functions depend upon dynamically unfolding brain network interactions. Autobiographical recollection – the autonoetic re-experiencing of context rich, emotionally laden, personally experienced episodes – is an excellent example of such a process. Autobiographical recollection unfolds over time, with different cognitive processes engaged at different times throughout. In this paper we apply a recently developed analysis technique – event related independent components analysis (eICA) – to study the spatiotemporal dynamics of neural activity supporting autobiographical recollection. Participants completed an in-scanner autobiographical recollection paradigm in which the recalled episodes varied in chronological age and emotional content. By combining eICA with these cognitive manipulations we show that the brain-wide response to autobiographical recollection comprises brain networks with (i) different sensitivities to psychological aspects of the to-be-recollected material and (ii) distinct temporal profiles of activity during recollection. We identified networks with transient activations (in language and cognitive control related regions) and deactivations (in auditory and sensorimotor regions) to each autobiographical probe question, as well as networks with responses that are sustained over the course of the recollection period. These latter networks together overlapped spatially with the broader default mode network (DMN), indicating subspecialisation within the DMN. The vividness of participants' recollection was associated with the magnitude of activation in left dorsolateral prefrontal cortex and deactivation in visual association cortices. We interpret our results in the context of current theories of the spatial and temporal organisation of the human autobiographical memory system. Our findings demonstrate the utility of eICA as a tool for studying higher cognitive functions. The application of eICA to high spatial and temporal resolution datasets identifies in a single experimental protocol spatially specific networks that are recruited during cognitive activity, as well as the temporal order of activation of these networks.

Plasticity of Visual Pathways and Function in the Developing Brain: Is the Pulvinar a Crucial Player?

The pulvinar is the largest of the thalamic nuclei in the primates, including humans. In the primates, two of the three major subdivisions, the lateral and inferior pulvinar, are heavily interconnected with a significant proportion of the visual association cortex. However, while we now have a better understanding of the bidirectional connectivity of these pulvinar subdivisions, its functions remain somewhat of an enigma. Over the past few years, researchers have started to tackle this problem by addressing it from the angle of development and visual cortical lesions. In this review, we will draw together literature from the realms of studies in nonhuman primates and humans that have informed much of the current understanding. This literature has been responsible for changing many long-held opinions on the development of the visual cortex and how the pulvinar interacts dynamically with cortices during early life to ensure rapid development and functional capacity Furthermore, there is evidence to suggest involvement of the pulvinar following lesions of the primary visual cortex (V1) and geniculostriate pathway in early life which have far better functional outcomes than identical lesions obtained in adulthood. Shedding new light on the pulvinar and its role following lesions of the visual brain has implications for our understanding of visual brain disorders and the potential for recovery.

Reduction of Interhemispheric Functional Brain Connectivity in Early Blindness: A Resting-State fMRI Study.

Objective The purpose of this study was to investigate the resting-state interhemispheric functional connectivity in early blindness by using voxel-mirrored homotopic connectivity (VMHC). Materials and Methods Sixteen early blind patients (EB group) and sixteen age- and gender-matched sighted control volunteers (SC group) were recruited in this study. We used VMHC to identify brain areas with significant differences in functional connectivity between different groups and used voxel-based morphometry (VBM) to calculate the individual gray matter volume (GMV). Results VMHC analysis showed a significantly lower connectivity in primary visual cortex, visual association cortex, and somatosensory association cortex in EB group compared to sighted controls. Additionally, VBM analysis revealed that GMV was reduced in the left lateral calcarine cortices in EB group compared to sighted controls, while it was increased in the left lateral middle occipital gyri. Statistical analysis showed the duration of blindness negatively correlated with VMHC in the bilateral middle frontal gyri, middle temporal gyri, and inferior temporal gyri. Conclusions Our findings help elucidate the pathophysiological mechanisms of EB. The interhemispheric functional connectivity was impaired in EB patients. Additionally, the middle frontal gyri, middle temporal gyri, and inferior temporal gyri may be potential target regions for rehabilitation.

Investigating the relationship between multiple grip forces and BOLD signal in the Cerebellum and dentate nuclei of MS subjects

Investigating the relationship between multiple grip forces and BOLD signal in the Cerebellum and dentate nuclei of MS subjects

Evaluating the Signal Processing Capacities of Post-Mortem Cerebral Cortical Tissue by Artificial Phototransduction of Dynamic Visual Stimuli

The signal processing function of human cerebral cortical tissues is determined by the regional cytoarchitectures distributed throughout the brain. Based upon this assumption, we pursued the hypothesis that residual microstructure within the primary and associative visual cortices of a fixed, post-mortem whole human brain would process electrical signals differentially. To this end, we designed and engineered a very simple brain-photocell interface. Photostimuli, presented as either periodic flashes or as dynamic visual images, were transduced by photocells attached to the optic nerve of a post-mortem human brain specimen. The novel approach revealed that microvolt fluctuations within the primary and associative visual cortices could be discriminated. Simple light-dark discrimination was noted for the primary visual area (BA17) whereas within the right occipito-parietal cortices of the dorsal visual stream (BA19, BA7), spectral power of microvolt fluctuations could discriminate moving visual stimuli from those which were non-moving. Discriminant analysis classified movement represented within the right parietal lobe with 80% success. Together, the results suggest that artificially generated electrical signals are processed differentially by alternative cortical regions in the post-mortem brain.

Altered functional brain connectivity in patients with visually induced dizziness.

BackgroundVestibular patients occasionally report aggravation or triggering of their symptoms by visual stimuli, which is called visually induced dizziness (VID). These patients therefore experience dizziness, discomfort, disorientation and postural unsteadiness. The underlying pathophysiology of VID is still poorly understood.ObjectiveThe aim of the current explorative study was to gain a first insight in the underlying neural aspects of VID.MethodsWe included 10 VID patients and 10 healthy matched controls, all of which underwent a resting state fMRI scan session. Changes in functional connectivity were explored by means of the intrinsic connectivity contrast (ICC). Seed-based analysis was subsequently performed in visual and vestibular seeds.ResultsWe found a decreased functional connectivity in the right central operculum (superior temporal gyrus), as well as increased functional connectivity in the occipital pole in VID patients as compared to controls in a hypothesis-free analysis. A weaker functional connectivity between the thalamus and most of the right putamen was measured in VID patients in comparison to controls in a seed-based analysis. Furthermore, also by means of a seed-based analysis, a decreased functional connectivity between the visual associative area and the left parahippocampal gyrus was found in VID patients. Additionally, we found increased functional connectivity between thalamus and occipital and cerebellar areas in the VID patients, as well as between the associative visual cortex and both middle frontal gyrus and precuneus.ConclusionsWe found alterations in the visual and vestibular cortical network in VID patients that could underlie the typical VID symptoms such as a worsening of their vestibular symptoms when being exposed to challenging visual stimuli. These preliminary findings provide the first insights into the underlying functional brain connectivity in VID patients. Future studies should extend these findings by employing larger sample sizes, by investigating specific task-based paradigms in these patients and by exploring the implications for treatment.

Visual Processing in the Ventral Pathway: Shape, Face, Color, Material Properties, and Stereoscopic Depth

The ventral visual pathway projecting from the primary visual cortex to the visual temporal association cortex processes shape, color, and material properties of objects as well as face and facial expression, and stereoscopic depth. The last decade has witnessed great advances in our understanding of how information is transformed at each transition between the stages along this pathway. Accumulating evidence also indicates that neurons in the later part of the pathway (e.g., area V4 and inferior temporal cortex) are causally involved in generating perception of shape, color, face, and fine stereoscopic depth.

Consciousness assessment by activated cerebral 18F-FDG PET complemented with the Wessex head injury matrix (WHIM) in patients with disorder of consciousness (DOC)

Cerebral 18F-FDG PET complements bedside examination with behavioural scales in patients with DOC enabling better functional categorization. We realized a resting PET, then another after motor/visual activation, in patients with DOC according to their clinical course. It is a retrospective mono central study in our acute inpatients rehabilitation unit between 2011 and 2014. Our group consists of 14 patients (whom 5 women) with DOC, 18–70 years old at moment of brain injury (6 severe TBI, 4 anoxia, 3 hemorrhagic and 1 ischemic major strokes). All had months after brain lesions (average delay 186 days), DOC assessment by the Wessex head injury matrix (WHIM), a basal resting state PET, followed by an activated one consisting on providing motor or visual stimulation during second PET. Distant WHIM was performed at least 6 months after (average 14.8 months). We defined 3 groups: (1) WHIM at [1–14], (2) WHIM at [15–29] and (3) WHIM at [30–58]. We analysed, by compared T test of each patient, metabolic increment between basal and activated PET-scan according to clinical course. All patients had initial significant increase of metabolism in the activated PET-scan compared with basal ones, but patterns were not always consistent with assigned task. But this significant activation (FWE [ P < 0,005]) was particularly located in left occipital, parietal and temporal associative areas, among patients with further best clinical course. All sever DOC had metabolic increase on activated PET-scan during first year post injury (average 6 months). Among patients with best clinical course we noticed that initial increased metabolism was located in left visual associative cortex and language/phonology treatment areas.