Kindling changes burst firing, neural synchrony and tonotopic organization of cat primary auditory cortex.

The effect of electrical kindling, applied twice daily in primary auditory cortex on the neural response properties and tonotopic organization in the lightly ketamine anesthetized cat is presented. Kindling refers to a highly persistent modification of brain functioning in response to repeated application of initially sub-convulsant electrical stimulation, typically in the limbic system but here in auditory cortex, which results in the development of epileptiform activity. Kindling resulted in approximately two-thirds of the animals reaching a fully generalized state in 40 stimulation sessions. Multi-unit recordings were obtained from primary auditory cortex contralateral to the kindled site. Spontaneous activity of single units in fully kindled animals showed a decrease in the mean firing rate compared to sham controls, and a reduction in the rate of burst firing as well as in the mean interspike interval in a burst as compared with normal and sham controls. A 40% enhancement of spontaneous neural synchrony, as measured by spike cross-correlation, was found. Hearing sensitivity, measured by auditory brainstem response, was not affected by the kindling sessions. A profound alteration of the tonotopic map in AI was observed with a large extent becoming tuned to similar high characteristic frequencies. The percentage of double tuned neurons was significantly increased, nevertheless the frequency-tuning curve bandwidth was on average reduced. Thus, electrical kindling resulted in substantial alterations in unit firing characteristics and reorganization of cat auditory cortex.