Abstract
The limbic system including the amygdala is responsible for learning using reward or punishment, and receives auditory inputs partly mediated by the auditory cortex (AC). We have reported that discrimination learning of sound sequences requires the presence of AC. Cortical neurons in AC are well activated by complex sound stimuli, which consist of harmonic overtones and have several formants. In the present study, we investigated possible roles of AC in discrimination leaning of complex sounds with multiple poles in the frequency spectrum. Water-deprived rats were trained to discriminate between two sounds of different spectral patterns. Licking a spout during presentation of one of the two (S+) was rewarded with water while the other (S-) was not. Either S+ or S- was presented randomly in a trial, which was repeated every one minute for 12 hours on consecutive 4 days. Percentage of trials in which rats licked the spout was calculated separately for S+ and S-, and test performance estimated as the difference was clearly increased during the test in control rats. To investigate the roles of AC, electrolytic lesion was bilaterally produced in AC. In the rats with AC lesions, test performance was significantly attenuated for discrimination learning between sounds with three or four poles in the frequency spectrum, while no significant effect of the lesion was found for discrimination between the stimuli with a pole or between pure tones. These findings indicate that AC plays a critical role in discrimination learning between sounds of complex spectrum patterns. [Jpn J Physiol 55 Suppl:S163 (2005)]
