REDUCED DYNAMIC RANGE TO COCHLEAR IMPLANT STIMULATION IN THE DORSAL ZONE OF CONGENITALLY DEAF CATS

The auditory dorsal zone (DZ) and suprasylvian sulcus of the visual cortex in cats process complex information of auditory and visual stimuli. Previous studies conducted by Land et al. (2016, 2018) suggested that the dorsal zone of the congenital deaf cats showed modest visual cross-modal plasticity while remaining responsive to cochlear implant (CI) stimulation. It remained unclear whether the presence of cross-modal plasticity alters the neural response dynamics in DZ when it is electrically stimulated. Here we compared the response dynamics in dorsal zone and antero/postero-medial lateral suprasylvian sulcus (A/PMLS) between congenitally deaf (n=6) and normal hearing (n=4) cats. The local field potential (LFP) responses to CI stimulation (randomised 9 intensities ranging from -2 below to 6 dB above eABR threshold) were recorded simultaneously in the DZ and visual area A/PMLS using 16-channel multielectrode arrays. We calculated the bipolar LFPs and time frequency representations (TFRs) along the array in both areas of interest. To further analyse the neural response dynamics, we selected the penetrations that exhibited the largest power and concentrated first on the evoked response. Although both groups showed monotonically increasing LFP amplitude with current level, deaf cats showed a reduced dynamic range in CI-evoked activity. Congenitally deaf cats also demonstrated lower cortical power of the alpha and beta frequency bands in DZ compared to normal hearing cats. Overall, these results suggest that congenital deafness alters neural response dynamics to cochlear implant stimulation also in the secondary area DZ.