Abstract
Learning is partly attributed to the functions of the neocortex. To investigate the roles of auditory cortex (AC) in a sound discrimination behavior, we investigated sound frequency discrimination by rats with or without AC lesion. Previously we reported that normal rats depend on relative difference for discriminating sound frequencies at narrow bandwidth (0.5 octave), while they depend on absolute frequency at wide bandwidth (1 octave). Now we report that AC lesion rats exhibited almost normal discrimination behaviors at both bandwidth between the rewarded (S+) and unrewarded (S-) sounds. After they learned to discriminate between 10 kHz (S+) and 5 kHz (S-) tones, however, they failed to discriminate between 20 kHz (S+) and 10 kHz (S-), while naïve and sham-operated rats could discriminate it. These results indicating that AC might have a critical role to re-learn the discrimination paradigm. The roles of AC were further tested with associative discrimination test, using 10kHz sound as S+ and 10kHz sound plus light as S-. In this test, AC lesion rats failed to discriminate between S+ of single modality and S- of multi modalities while normal rats performed well. The present results strongly suggest that AC works as an auditory interface to the neocortex, which are responsible for flexible learning or association of sensory information with mixed modalities. [Jpn J Physiol 55 Suppl:S163 (2005)]
