Auditory cortex lesions and discrimination of spatial location by the rat

Five normal rats and four rats with bilateral lesions of auditory cortex were tested by the conditioned suppression procedure to determine their abilities to discriminate between spatially separated sound sources. The discrimination involved detection of a change in location of a train of clicks from a speaker on the animals' left to a speaker on the right. The separation between speakers was varied from 180 degrees to 90 degrees, 45 degrees, 22 degrees, 12 degrees, 6 degrees, and psychophysical functions were obtained using a method of descending limits. Both normal and brain-damaged animals were capable of discriminating left from right clicks and psychophysical curves were similar for the two groups. Histological analysis indicated that the lesions in each of the four brain-damaged rats destroyed primary auditory cortex as well as surrounding belt areas. Therefore, for the rat, auditory cortex was not found to be essential for discrimination of the spatial locations of auditory stimuli. The results are discussed in light of impairments in sound localization following lesions of auditory cortex in other mammalian species.