Abstract
Cortical areas are highly interconnected both via cortical and subcortical pathways, and primary sensory cortices are not isolated from this general structure. In primary sensory cortical areas, these pre-existing functional connections serve to provide contextual information for sensory processing and can mediate adaptation when a sensory modality is lost. Cross-modal plasticity in broad terms refers to widespread plasticity across the brain in response to losing a sensory modality, and largely involves two distinct changes: cross-modal recruitment and compensatory plasticity. The former involves recruitment of the deprived sensory area, which includes the deprived primary sensory cortex, for processing the remaining senses. Compensatory plasticity refers to plasticity in the remaining sensory areas, including the spared primary sensory cortices, to enhance the processing of its own sensory inputs. Here, we will summarize potential cellular plasticity mechanisms involved in cross-modal recruitment and compensatory plasticity, and review cortical and subcortical circuits to the primary sensory cortices which can mediate cross-modal plasticity upon loss of vision.
Highlights
It is well established that sensory experience can alter cortical and subcortical circuits, especially during early development
This study demonstrated that primary visual cortex (V1) activity was essential for enhanced learning of braille reading in blindfolded individuals by showing that transcranial magnetic stimulation (TMS) of V1 removes this advantage in blindfolded adults
This study further demonstrated that sound activates a disinhibitory circuit in layer 1 (L1) and layer 2/3 (L2/3) involving vasoactive intestinal peptide-positive (VIP) and somatostatin-positive (SOM) interneurons, which is mediated by a direct functional connection from primary auditory cortex (A1) layer 5 (L5) that arrives through V1 L1 (Ibrahim et al, 2016)
Summary
It is well established that sensory experience can alter cortical and subcortical circuits, especially during early development. In addition to these local inputs, V1 L2/3 neurons receive multisensory information from other cortical areas via direct long-range intracortical connections, as well as indirectly via subcortical structures (Figure 5; ‘‘Subcortical Sources of Inputs to V1 L2/3 That Can Mediate Cross-modal Recruitment’’ section).
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