The Effects Of Frequency Discrimination Training On Tonotopic Organization In The Primary Auditory Cortex Of Adult Rats

Previous studies have shown that mammals at young age exhibit high degree of plasticity in primary auditory cortex (A1). Though the plasticity in adults A1 can still be observed, the plasticity is significantly declined compared with that in mammal pups. Auditory neurons with various characteristic frequencies (CFs) in A1 distribute in a systematic order, i.e., exhibiting a tonotopic organization. The change of tonotopic organization in Al can be regard as an index to show the plasticity in A1.The ability to discriminate different sound frequency is one of the most important functions of auditory system. Therefore, the aim of the present study was to investigate if frequency discrimination training could induce the change of tonotopic organization in Al and induce auditory cortex plasticity. Rats were divided into two groups:training group (adult rats that undergo sound frequency discrimination training), and control group (age-matched adult rats without frequency discrimination training). We used electrophysiological techniques to record single neuron activity in the primary auditory cortex of adult rats, to determine whether long-term frequency discrimination training can induce the change of tonotopic organization in Al. Our results indicated that, rats with frequency discrimination training showed a significant change in the tonotopic organization in Al. The representative area of neurons with their CFs in the range of 8-15 kHz which closed to the target frequency (10 kHz) used for behavioral training was significantly enlarged. In addition, we found that neurons with lower CFs (4-15 kHz) emerged in the high CF (32-40 kHz) area, showing a tendency of reorganization in high frequency representative area (32-40 kHz). These results suggest that the primary auditory cortex in adult rats still have some degree of plasticity, and the plasticity can be induced through behavioral training.