Acute spiral ganglion lesions change the tuning and tonotopic organizationof cat inferior colliculus neurons

Many studies have reported plastic changes in central auditory frequency or ganization after chronic cochlear lesions. These studies employed mechanica l, acoustic or drug-induced disruptions of restricted regions of the organ of Col ti that permanently alter its tuning and sensitivity and require an extended recovery period before central effects can be measured. In this st udy, mechanical lesions were made to 1 mm sectors of the spiral ganglion (S G). These lesions remove a restricted portion of the cochlear output, but l eave the organ of Corti and basilar membrane intact. Multiunit mapping asse ssed the pre- and post-lesion tonotopic organization of the inferior collic ulus (IC). Immediately after SG lesions, IC neurons previously tuned to the lesion frequencies became less sensitive to those frequencies but more sen sitive to lesion edge frequencies, resulting in a shift in their characteri stic frequencies (CFs). Notches in the excitatory response areas at frequen cies corresponding to the lesion frequencies and expansion of spatial tunin g curves were also observed. CFs of neurons tuned to unlesioned frequencies were unchanged. These results suggest that 'plastic' changes similar to th ose observed after long survival times in previous studies require little o r no experience and occur within minutes to hours following the lesion. (C) 2000 Elsevier Science B.V. All rights reserved.