Deafness induces complete crossmodal plasticity in a belt region of dorsal auditory cortex

Many neural areas, where patterned activity is lost following deafness, have the capacity to become activated by the remaining sensory systems. This crossmodal plasticity can be measured at perceptual/behavioural as well as physiological levels. The dorsal zone (DZ) of auditory cortex of deaf cats is involved in supranormal visual motion detection, but its physiological level of crossmodal reorganisation is not well understood. The present study of early‐deaf DZ (and hearing controls) used multiple single‐channel recording methods to examine neuronal responses to visual, auditory, somatosensory and combined stimulation. In early‐deaf DZ, no auditory activation was observed, but 100% of the neurons were responsive to visual cues of which 21% were also influenced by somatosensory stimulation. Visual and somatosensory responses were not anatomically organised as they are in hearing cats, and fewer multisensory neurons were present in the deaf condition. These crossmodal physiological results closely correspond with and support the perceptual/behavioural enhancements that occur following hearing loss. Activity of neurons in the higher‐order auditory area DZ of hearing and early‐deaf cats were collected in response to different unisensory and multisensory stimuli. In hearing cats, almost all neurons responded to auditory stimuli and a considerable number of neurons (more than 76%) responded to visual stimuli. However, in early‐deaf cats no auditory responses were observed in this auditory area while all neurons exhibited visual responses. This crossmodal plasticity is in line with the supranormal visual ability of deaf subjects.