Differential representation of species-specific primate vocalizations in the auditory cortices of marmoset and cat.

A number of studies in various species have demonstrated that natural vocalizations generally produce stronger neural responses than do their time-reversed versions. The majority of neurons in the primary auditory cortex (A1) of marmoset monkeys responds more strongly to natural marmoset vocalizations than to the time-reversed vocalizations. However, it was unclear whether such differences in neural responses were simply due to the difference between the acoustic structures of natural and time-reversed vocalizations or whether they also resulted from the difference in behavioral relevance of both types of the stimuli. To address this issue, we have compared neural responses to natural and time-reversed marmoset twitter calls in A1 of cats with those obtained from A1 of marmosets using identical stimuli. It was found that the preference for natural marmoset twitter calls demonstrated in marmoset A1 was absent in cat A1. While both cortices responded approximately equally to time-reversed twitter calls, marmoset A1 responded much more strongly to natural twitter calls than did cat A1. This differential representation of marmoset vocalizations in two cortices suggests that experience-dependent and possibly species-specific mechanisms are involved in cortical processing of communication sounds.