Motion-onset visually evoked potentials are amplified in the deaf

The loss of a sensory modality triggers a phenomenon known as cross-modal plasticity, where areas of the brain responsible for the lost sensory modality are reorganized and repurposed to the benefit of the remaining modalities. After perinatal or congenital deafness, superior visual motion detection abilities have been psychophysically identified in both humans and cats, and this advantage has been causally demonstrated to be mediated by reorganized auditory cortex. In our study, we investigated visually evoked potentials (VEPs) in response to motion-onset stimuli of varying speeds in both hearing and perinatally deafened cats under light anesthesia. Although the peak latencies did not differ between the two groups, we observed significantly greater VEP amplitudes in deaf cats, specifically in the P1 component and the signal power of the overall waveform. Through sigmoidal modeling, we identified that the speed offset and steepness at the threshold for 50% maximum neural activity was unchanged, showing that neuronal activity was modulated by motion speeds in a comparable manner between the hearing and deaf subjects and the deaf had greater potentials at all dot speeds. Our results suggest that the increased cortical activity by the auditory and visual cortices of deaf cats may account for their superior behavioral advantage in motion detection and indicates that cross-modal plasticity plays a significant role in the cortical processing of motion. NEW & NOTEWORTHY The present study investigated cross-modal plasticity after perinatal deafness in cats using motion-onset visually evoked potentials. Deaf animals were observed to have significantly greater evoked potentials in both peak components and the signal power of the overall waveforms. These results are discussed in relation to prior studies on deaf subjects in both human and animal research on evoked potentials and psychophysics.