Acoustic parameters underlying vocalization-sensitive neural responses in Rhesus monkey auditory cortex

The vocal behavior of macaque monkeys has been studied extensively in both field and laboratory settings. To date, however, no investigation has systematically examined the neural mechanisms underlying species-specific recognition of their vocalizations. To bridge this gap, we are investigating the auditory representation of conspecific vocalizations in the neocortex of behaving rhesus monkeys. Subjects performed a simple auditory detection task during which, on each trial, they listened to a conspecific vocalization followed by a non-vocal, target sound. The stimulus set consisted of call types familiar to our captive-bred subjects but from unknown individuals: three exemplars from each of 7 call categories. Our preliminary investigation using these natural stimuli (Ghazanfar et al, SFN 2002) revealed that ~45 of auditory belt cortical multi-units were selective for 1 or 2 call categories. This suggests that the macaque auditory cortex is specialized to process communication sounds. To assess the degree of this specialization and the specificity of vocalization-sensitivity, we are comparing single-unit responses to vocalizations with time-reversed versions, pure-tones and band-passed noise. For each vocalization, a pure-tone and a band-passed noise stimulus were generated to match the signal’s duration, dominant frequency and average RMS power. Recordings from both core and belt cortical areas will determine whether vocalization-sensitive neurons in these regions are driven by simple features of the signal or by more complex interactions between spectral and temporal properties