Single unit analysis of auditory processing in squirrel monkey frontal cortex.

Clicks, tone bursts and species-specific vocalizations were used to test 315 units isolated in the dorsolateral prefrontal cortex. Acoustic responses were detected in about 20% of the units. Responsive units were scattered throughout the explored area, although more units responsive to vocalizations were found in the vicinity of sulcus principalis. Vocalizations were effective stimuli, driving 68% of the acoustic units. However, only 19% responded exclusively to vocalizations. Clicks were effective for 65% of the acoustic units, 27% of which responded only to clicks. Tones activated 39% of the acoustic units. Units generally responded to tones over a wide frequency range. Responses to tones, clicks and vocalization were similar, both within the same unit and between units. The biggest difference related to the background activity of the unit: Low rate cells produced a small number of relatively well-timed discharges per stimulus; high rate cells produced a longer, more poorly-timed response. Vocalizations differed in their effectiveness according to their physical structure. Noisy calls elicited 69% of all responses, although they accounted for only one-third of the test vocalizations. We conclude that frontal acoustic units are involved with at least two functional mechanisms, one related to attending to a large class of sounds, the other related to the detection of sounds with high motivational significance.