Spontaneous firing activity of cortical neurons in adult cats with reorganized tonotopic map following pure-tone trauma

We hypothesized that moderate sensorineural hearing loss resulting from aco ustic trauma would cause (i) a change in the cortical tonotopic map, (ii) a n increase in spontaneous activity in the reorganized region and (iii) incr eased inter-neuronal synchrony within the reorganized part of the cortex. F ive kittens were exposed to a 126 dB sound pressure limit tone of 6 kHz for 1 h at both 5 and 6 weeks of age. Recordings were performed 7-16 weeks aft er the exposure. Auditory brainstem response thresholds for frequencies abo ve 12 kHz were increased by 30 dB on average relative to those in normal ca ts. Tonotopic maps in the primary auditory cortex were reorganized in such a way that the area normally tuned to frequencies of 10-40 kHz was now enti rely tuned to 10 kHz. Spontaneous firing rates were significantly higher in reorganized areas than in normal areas. In order to test for changes in in ter-neuronal synchrony, cross-correlation analysis was done on 225 single-u nit pairs recorded in the traumatized cats. For the single- and dual-electr ode pairs there was no significant difference in peak cross-correlation coe fficients for the firings of simultaneously recorded cells between normal a nd reorganized areas. However, the percentage of correlations that differed significantly from zero was higher in the reorganized area than in the nor mal area. This suggests a potential correlation between cortical reorganiza tion, increased spontaneous firing rare and inter-neuronal synchrony that m ight be related to tinnitus found in high-frequency hearing loss induced by acoustic trauma.