Does insular cortex lesion cause tinnitus in rats?

OBJECTIVE(S): Tinnitus is defined as ringing of the ears that is experienced when there is no external sound source, and is an auditory phantom sensation. The insula as a multimodal cortex has been shown to be involved in the processing of auditory stimuli rather than other sensory and motor processing and reported to correlate with some aspects of tinnitus. However, its exact role is not clear. The present study aimed to investigate the effect of excitotoxic lesions limited to the insular cortex on the ability to detect a gap in background noise. MATERIALS AND METHODS: Gap detection test and prepulse inhibition, two objective measurements of auditory startle response, were measured, in 33 male Wistar rats, before and up to four weeks after insular lesion in three experimental groups (sham, control, and lesion). RESULTS: The ability to detect the gap interposed between 60 db background noise was impaired at weeks 2, 3, and 4 following insular lesion, while prepulse inhibition remained intact up to four weeks after surgery. CONCLUSION: These findings indicated that excitotoxic lesions of the insular cortex may produce a tinnitus-like phenomenon in rats while sparing the hearing sensitivity; suggesting that the insular cortex may have a role in the development of tinnitus.