The Effects Of Frequency Discrimination Training On The Characteristics Of Frequency Tuning Of Neurons In The RatAuditory Cortex

The plasticity of auditory cortex has been found in both young and adult animals. However, the auditory cortical plasticity was lower in adulthood compared to that at young age. In adult animals, the auditory cortical plasticity can be induced by the establishment of sound stimulation related conditioned reflex. In the present study, we trained SD adult rats to discriminate sounds with different frequencies and to study the differences in the frequency tuning characteristics of A1 neurons between training rats with frequency discrimination training and age-matched control rats without training. This will provide experimental basis for further understanding of the plasticity of auditory cortex in adult animals.The experiment was conducted in two groups of rats:training group (trained to discriminate 10 kHz target sound and 6 kHz non-target sound) and control group (without training). Using the electrophysiological recording technique, we recorded the responses of single neurons in the primary auditory cortex (A1) of rats to various sound frequencies and intensities, and studied the frequency-level response areas (FLRAs) of A1 neurons in adult rats of both training group and control group. We also compared the differences in the characteristic frequency (CF), best frequency (BF), minimum threshold (MT), bandwidth of frequency tuning curves of auditory neurons between the rats in training group and the rats in control group.The results showed that frequency discrimination training induced more "multi peaks", "double peaks", and "narrow" type neurons of FLRA in training group compared to that in control group. There is a great proportion of neurons with their CFs distributed over the range of trained sound frequencies in the training group than that in the control group. Compared with control group, frequency discrimination training induces a greater proportion of neurons whose BFs shifted to the frequency range of training sounds in the training group. This effect was more evident for neurons with their CF at the high frequency region (>20 kHz). However, frequency discrimination training has no significant effects on the degree of MT and sharpening frequency tuning of A1 neurons.The research results show that frequency discrimination training induced plasticity of A1 neurons in the adult rats. Frequency discrimination training affected the CF, BF and FLRA type of A1 neurons, and induced more A1 neurons tuning to the training sound frequency.