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Brain (re)organization following visual loss

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The study of the neural consequences of sensory loss provides a unique window into the brain's functional and organizational principles. Although the blind visual cortex has been implicated in the cross‐modal processing of nonvisual inputs for quite some time, recent research has shown that certain cortical organizational principles are preserved even in the case of complete sensory loss. Furthermore, a growing body of work has shown that markers of neuroplasticity extend to neuroanatomical metrics that include cortical thickness and myelinization. Although our understanding of the mechanisms that underlie sensory deprivation‐driven cross‐modal plasticity is improving, several critical questions remain unanswered. The specific pathways that underlie the rerouting of nonvisual information, for instance, have not been fully elucidated. The fact that important cross‐modal recruitment occurs following transient deprivation in sighted individuals suggests that significant rewiring following blindness may not be required. Furthermore, there are marked individual differences regarding the magnitude and functional relevance of the cross‐modal reorganization. It is also not clear to what extent precise environmental factors may play a role in establishing the degree of reorganization across individuals, as opposed to factors that might specifically relate to the cause or the nature of the visual loss. In sum, although many unresolved questions remain, sensory deprivation continues to be an excellent model for studying the plastic nature of the brain. This article is categorized under: Psychology > Brain Function and Dysfunction Psychology > Perception and Psychophysics Neuroscience > Plasticity
Illustration of the link between cortical thickness and auditory behavior. The left panel illustrates the result of a whole‐brain vertex‐wise regression analysis depicting the areas where cortical thickness best predicted the performance of blind individuals on an auditory discrimination task (adapted with permission from Voss & Zatorre, ). The right panel illustrates the result of a linear interaction model to ascertain how the covariation between the thickness of occipital seed (using the result from the left panel) and the thickness across the rest of the cortex in early blind individuals varied as a function of performance on an auditory discrimination task. It was shown that the performance of the early blind was strongly predicted by the strength of the cortical covariance between the occipital cortex and intraparietal sulcus (IPS), a region for which cortical thickness in sighted individuals was previously shown to predict performance in the same task (adapted with permission from Voss & Zatorre, )
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Illustration of how neuromodulators can be combined with behavioral training to promote cortical plasticity. Illustrated in the top row are overlap maps of A1 responsiveness to training tones in young rodents, whereas A1 maps of aged rodents are illustrated in the bottom row. Blue polygons represent areas activated by target tones (5 kHz), green polygons represent areas activated by distractor tones (10 kHz), and the pink polygons indicate areas of the A1 map that were activated by both frequencies. Compared to control animals (left column), auditory training (center column) produced a dramatic reduction in the overlapping area (by 30% in the young and 36% in the old), and this reduction was further increased by the administration of a cholinergic enhancer (right column) in rodents also receiving auditory training (by another 30% in the young and 37% in the old). The cholinergic enhancement thus further improved the average ability of A1 neurons to properly discriminate between tones (adapted with permission from Voss et al., )
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Illustration of the dissociation between anatomical changes that are the direct result of sensory deprivation and consequent atrophy and those related to compensatory reorganization and behavioral adaptations. The left panel illustrates brain areas where the magnetization transfer ratio (MTR; a proxy for myelin content) is significantly more elevated in the early blind relative to sighted controls (EARLY – SIGHTED), whereas the center panel illustrates brain areas where the MTR is significantly reduced in the early blind (SIGHTED – EARLY). The right panel illustrates brain areas where MTR was found to significantly correlate with performance on an auditory discrimination task; note the correspondence between the regions highlighted in the left and right panels, demonstrating the adaptive and compensatory nature of the change in myelin (adapted with permission from Voss et al., )
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Neuroscience > Plasticity
Psychology > Perception and Psychophysics
Psychology > Brain Function and Dysfunction

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