Crossmodale Plastizität in der Grenzregion zwischen auditorischem und visuellem Kortex und Auswirkungen auf die Verarbeitung auditorischer Informationen bei adult-ertaubten Ratten

The ability of the brain to adapt to adult-onset deafness has implications for hearing restoration with cochlear implants (CI). Compensatory cross-modal plasticity between visual and auditory cortex, as well as intra-modal plasticity, may influence the outcome of CI. Moreover, hearing loss may affect neural processing of auditory information in the medial prefrontal cortex (mPFC) as a representative for cognitive function. Here, we investigate the neural processing of CI stimulation in the transition zone between auditory and visual cortices and in the mPFC six months after deafness-onset in adult rats.

Male Sprague-Dawley rats were deafened by intracochlear neomycin injection (n=8), and normal hearing rats served as controls (n=8). After recovery, rats were trained for six months to respond to brief visual stimuli in the Five Choice Serial Reaction Time Task (5CSRTT). After that, anaesthetized deaf rats and hearing controls (acutely deafened) were implanted with CIs and neural activity was recorded via 32-channel silicon probes across the transition zone between auditory and visual cortices and in the mPFC during CI and visual stimulation.

Chronic adult-onset deafness caused a shift in the auditory-visual border, with activity during visual stimulation expanding into the auditory cortex, but without expanding into the core auditory region (p<0.05). The power of the cochlear implant-evoked responses within the auditory cortex was weaker in deafened rats (p<0.05). Combined auditory and visual stimulation did not substantially affect auditory activation. In the mPFC, neural activity was moderately increased during visual stimulation in deafened rats, but not during CI stimulation.

Our findings show that "cross-modal plasticity" between visual and auditory cortices in adult-onset deafness is primarily a local effect, without affecting core auditory regions. In addition, although intramodal changes are present in the auditory cortex, they remain comparable between chronically deafened adult rats and normal hearing controls. These plastic changes after adult-onset deafness may be addressed by appropriate CI stimulation.