Amplified extrastriate visual cortical projections to the dorsal zone of auditory cortex following early- and late-onset deafness

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Adaptive cross-modal plasticity refers to cortical reorganization that takes place across sensory modalities following the loss of a sensory system. This loss of one modality is often accompanied by a heightening of the remaining senses (Bavelier and Neville, 2002). Cat auditory cortex has been shown to undergo cross-modal reorganization following deafness, such that deaf animals are better able to detect visual motion than hearing controls, an advantage which can be localized to the dorsal zone (DZ) of auditory cortex (Lomber et al., 2010). However, because the structural adaptations that might subserve this plasticity remain largely unknown, the purpose of the present investigation was to examine modifications in anatomical connectivity following early- or late-onset deafness. We injected DZ of hearing, early- and late-deafened cats ( n = 5 per group) with biotinylated dextran amine (BDA). Immunohistochemistry was performed following perfusion to reveal the tracer. Overall, the pattern of cortical projections to DZ was similar in both early- and late-deafened cats and hearing controls. However, an increase in projection strength from visual areas involved in visual motion processing was observed in both early- and late-deafened animals compared to hearing controls. Our observations suggest that amplified cortical projections from visual motion processing regions to DZ may underlie the cross-modal reorganization that functionally manifests as superior visual motion detection abilities in the deaf animal. Furthermore, the degree to which this reorganization occurs is similar between early- and late-deafened animals, suggesting that structural compensations can occur regardless of duration of acoustic experience.