Representation of the cochlea in the neocortex of guinea pigs.

By recording unit clusters and local evoked responses in the auditory cortex of guinea pigs the cortical representation of best frequencies was studied. In penetrations vertical to the cortical surface best frequencies were similar. Parallel to the cortical surface, however, different frequencies were found in the antero-posterior direction, whereas medio-laterally best frequencies usually remained in the same range (isofrequency stripes). Two auditory cortical fields could be distinguished, which are tonotopically organized. With increasing sound intensity the cortical response field for a given frequency and thus the frequency overlap increased. All along the isofrequency stripes in the medio-lateral direction, the stimulation of the contralateral ear produces larger responses than the same stimulus delivered to the ipsilateral ear.