Abstract
I obtained 118 extracellular single-unit recordings from the medial geniculate body (MG) in unanesthetized guinea pigs, and studied responses of the MG neurons to pure tone stimuli and to species-specific vocalized sounds. About 20% of the MG neurons were more sharply tuned to the characteristic frequency (CF) than primary neurons. These sharply tuned neurons were mainly located in the ventral division. Of 79 neurons with a CF within the frequency range of the vocalized sound, only 23 neurons (29%) responded to the vocalized sound in the response pattern that was predicted from the response properties to pure tone stimuli. Five neurons (6%) were inhibited by the vocalized sound, and 24 neurons (30%) had no response to the vocalized sound. The neurons responding in each way seemed to be distributed equally in the different subdivisions. One MG neuron had no response to any pure tone but a strong excitatory response to one vocalized sound. The responsiveness and predictability of MG neurons to the vocalized sound were low. These results suggest the presence of the neurons described as the feature detectors in the sub-cortical MG level.
