What is the function of auditory cortex when it develops in the absence of acoustic input?

•Auditory cortex of the deaf is recruited to perform enhanced visual functions.•Specific visual functions are localized to distinct portions of deaf auditory cortex.•Crossmodal plasticity switches sensory, but not behavioural, roles of auditory cortex.

When the brain is deprived of input from one sensory modality, it often compensates with supranormal performance in one or more of the intact sensory systems. Therefore, we were interested in examining the function of auditory cortex when it is deprived of normal acoustic input. In this context, it has been proposed that auditory cortex of the deaf may be recruited to perform visual functions. Here, we review recent evidence of a causal link between supranormal visual performance and visual activity in reorganized deaf auditory cortex. Furthermore, we considered that if auditory cortex does mediate the enhanced visual abilities of the deaf, are these functions distributed uniformly across deaf auditory cortex, or are specific functions differentially localized to distinct portions of the affected cortices? Finally, we considered whether reorganized cortex retains any relationship to functions performed in these regions in hearing subjects. These fundamental questions are of significant clinical importance as restoration of hearing in prelingually deaf children is possible with cochlear prosthetics.