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Handbook of Clinical Neurology 2022Blindness is a common sequela after stroke affecting the primary visual cortex, presenting as a contralesional, homonymous, visual field cut. This can occur unilaterally... (Review)
Review
Blindness is a common sequela after stroke affecting the primary visual cortex, presenting as a contralesional, homonymous, visual field cut. This can occur unilaterally or, less commonly, bilaterally. While it has been widely assumed that after a brief period of spontaneous improvement, vision loss becomes stable and permanent, accumulating data show that visual training can recover some of the vision loss, even long after the stroke. Here, we review the different approaches to rehabilitation employed in adult-onset cortical blindness (CB), focusing on visual restoration methods. Most of this work was conducted in chronic stroke patients, partially restoring visual discrimination and luminance detection. However, to achieve this, patients had to train for extended periods (usually many months), and the vision restored was not entirely normal. Several adjuvants to training such as noninvasive, transcranial brain stimulation, and pharmacology are starting to be investigated for their potential to increase the efficacy of training in CB patients. However, these approaches are still exploratory and require considerably more research before being adopted. Nonetheless, having established that the adult visual system retains the capacity for restorative plasticity, attention recently turned toward the subacute poststroke period. Drawing inspiration from sensorimotor stroke rehabilitation, visual training was recently attempted for the first time in subacute poststroke patients. It improved vision faster, over larger portions of the blind field, and for a larger number of visual discrimination abilities than identical training initiated more than 6 months poststroke (i.e., in the chronic period). In conclusion, evidence now suggests that visual neuroplasticity after occipital stroke can be reliably recruited by a range of visual training approaches. In addition, it appears that poststroke visual plasticity is dynamic, with a critical window of opportunity in the early postdamage period to attain more rapid, more extensive recovery of a larger set of visual perceptual abilities.
Topics: Adult; Blindness, Cortical; Humans; Primary Visual Cortex; Stroke; Stroke Rehabilitation; Vision, Ocular; Visual Perception
PubMed: 35034749
DOI: 10.1016/B978-0-12-819410-2.00030-8 -
Nature Nov 2022Neuropsychiatric disorders classically lack defining brain pathologies, but recent work has demonstrated dysregulation at the molecular level, characterized by...
Neuropsychiatric disorders classically lack defining brain pathologies, but recent work has demonstrated dysregulation at the molecular level, characterized by transcriptomic and epigenetic alterations. In autism spectrum disorder (ASD), this molecular pathology involves the upregulation of microglial, astrocyte and neural-immune genes, the downregulation of synaptic genes, and attenuation of gene-expression gradients in cortex. However, whether these changes are limited to cortical association regions or are more widespread remains unknown. To address this issue, we performed RNA-sequencing analysis of 725 brain samples spanning 11 cortical areas from 112 post-mortem samples from individuals with ASD and neurotypical controls. We find widespread transcriptomic changes across the cortex in ASD, exhibiting an anterior-to-posterior gradient, with the greatest differences in primary visual cortex, coincident with an attenuation of the typical transcriptomic differences between cortical regions. Single-nucleus RNA-sequencing and methylation profiling demonstrate that this robust molecular signature reflects changes in cell-type-specific gene expression, particularly affecting excitatory neurons and glia. Both rare and common ASD-associated genetic variation converge within a downregulated co-expression module involving synaptic signalling, and common variation alone is enriched within a module of upregulated protein chaperone genes. These results highlight widespread molecular changes across the cerebral cortex in ASD, extending beyond association cortex to broadly involve primary sensory regions.
Topics: Humans; Autism Spectrum Disorder; Cerebral Cortex; Neurons; RNA; Transcriptome; Autopsy; Sequence Analysis, RNA; Primary Visual Cortex; Neuroglia; Genetic Variation
PubMed: 36323788
DOI: 10.1038/s41586-022-05377-7 -
Nature May 2023Sensory processing in the neocortex requires both feedforward and feedback information flow between cortical areas. In feedback processing, higher-level representations...
Sensory processing in the neocortex requires both feedforward and feedback information flow between cortical areas. In feedback processing, higher-level representations provide contextual information to lower levels, and facilitate perceptual functions such as contour integration and figure-ground segmentation. However, we have limited understanding of the circuit and cellular mechanisms that mediate feedback influence. Here we use long-range all-optical connectivity mapping in mice to show that feedback influence from the lateromedial higher visual area (LM) to the primary visual cortex (V1) is spatially organized. When the source and target of feedback represent the same area of visual space, feedback is relatively suppressive. By contrast, when the source is offset from the target in visual space, feedback is relatively facilitating. Two-photon calcium imaging data show that this facilitating feedback is nonlinearly integrated in the apical tuft dendrites of V1 pyramidal neurons: retinotopically offset (surround) visual stimuli drive local dendritic calcium signals indicative of regenerative events, and two-photon optogenetic activation of LM neurons projecting to identified feedback-recipient spines in V1 can drive similar branch-specific local calcium signals. Our results show how neocortical feedback connectivity and nonlinear dendritic integration can together form a substrate to support both predictive and cooperative contextual interactions.
Topics: Animals; Mice; Calcium; Dendrites; Visual Cortex; Visual Pathways; Feedback, Physiological; Primary Visual Cortex; Pyramidal Cells; Optogenetics; Calcium Signaling
PubMed: 37138089
DOI: 10.1038/s41586-023-06007-6 -
Frontiers in Neural Circuits 2018All neuronal circuits are subject to neuromodulation. Modulatory effects on neuronal processing and resulting behavioral changes are most commonly reported for higher... (Review)
Review
All neuronal circuits are subject to neuromodulation. Modulatory effects on neuronal processing and resulting behavioral changes are most commonly reported for higher order cognitive brain functions. Comparatively little is known about how neuromodulators shape processing in sensory brain areas that provide the signals for downstream regions to operate on. In this article, we review the current knowledge about how the monoamine neuromodulators serotonin, dopamine and noradrenaline influence the representation of sensory stimuli in the mammalian sensory system. We review the functional organization of the monoaminergic brainstem neuromodulatory systems in relation to their role for sensory processing and summarize recent neurophysiological evidence showing that monoamines have diverse effects on early sensory processing, including changes in gain and in the precision of neuronal responses to sensory inputs. We also highlight the substantial evidence for complementarity between these neuromodulatory systems with different patterns of innervation across brain areas and cortical layers as well as distinct neuromodulatory actions. Studying the effects of neuromodulators at various target sites is a crucial step in the development of a mechanistic understanding of neuronal information processing in the healthy brain and in the generation and maintenance of mental diseases.
Topics: Animals; Auditory Cortex; Dopamine; Humans; Norepinephrine; Perception; Sensation; Serotonin; Somatosensory Cortex; Visual Cortex
PubMed: 30042662
DOI: 10.3389/fncir.2018.00051 -
Current Biology : CB May 2021How many thalamic neurons converge onto a cortical cell? This is an important question, because the organization of thalamocortical projections can influence the...
How many thalamic neurons converge onto a cortical cell? This is an important question, because the organization of thalamocortical projections can influence the cortical architecture. Here, we estimate the degree of thalamocortical convergence in primary visual cortex by taking advantage of the cortical expansion-neurons within a restricted volume in primary visual cortex have overlapping receptive fields driven by a smaller set of inputs from the lateral geniculate nucleus. Under these conditions, the measurements of cortical receptive fields in a population can be used to infer the receptive fields of their geniculate inputs and the weights of their projections using non-negative matrix factorization. The analysis reveals sparse connectivity, where a handful (~2-6) of thalamic inputs account for 90% of the total synaptic weight to a cortical neuron. Together with previous findings, these results paint a picture consistent with the idea that convergence of a few inputs partly determine the retinotopy and tuning properties of cortical cells..
Topics: Animals; Geniculate Bodies; Neurons; Primary Visual Cortex; Thalamus
PubMed: 33705713
DOI: 10.1016/j.cub.2021.02.032 -
ELife Aug 2018The ongoing debate on the neural basis of orientation selectivity in the primary visual cortex continues.
The ongoing debate on the neural basis of orientation selectivity in the primary visual cortex continues.
Topics: Orientation; Orientation, Spatial; Photic Stimulation; Visual Cortex; Visual Perception
PubMed: 30106374
DOI: 10.7554/eLife.39762 -
Frontiers in Neural Circuits 2021Lesion or damage to the primary visual cortex (V1) results in a profound loss of visual perception in humans. Similarly, in mice, optogenetic silencing of V1 profoundly... (Review)
Review
Lesion or damage to the primary visual cortex (V1) results in a profound loss of visual perception in humans. Similarly, in mice, optogenetic silencing of V1 profoundly impairs discrimination of orientated gratings. V1 is thought to have such a critical role in perception in part due to its position in the visual processing hierarchy. It is the first brain area in the neocortex to receive visual input, and it distributes this information to more than 18 brain areas. Here I review recent advances in our understanding of the organization and function of the V1 projections in the mouse. This progress is in part due to new anatomical and viral techniques that allow for efficient labeling of projection neurons. In the final part of the review, I conclude by highlighting challenges and opportunities for future research.
Topics: Animals; Mice; Neurons; Optogenetics; Primary Visual Cortex; Visual Cortex; Visual Pathways; Visual Perception
PubMed: 34867213
DOI: 10.3389/fncir.2021.751331