Frontal cortex activity underlying the production of diverse vocal signals during social communication in marmoset monkeys

Vocal communication is essential for social behaviors in humans and many non-human primates. While the frontal cortex has been shown to play a crucial role in human speech production, its role in vocal production in non-human primates has long been questioned. Recent studies have shown activation in single neurons in the monkey frontal cortex during vocal production in relatively isolated environment. However, little is known about how the frontal cortex is engaged in vocal production in ethologically relevant social context, where different types of vocal signals are produced for various communication purposes. Here we studied single neuron activities and local field potentials (LFP) and in the frontal cortex of marmoset monkeys while the animal engaged in vocal exchanges with other conspecifics in a social environment. Marmosets most frequently produced four types of vocalizations with distinct acoustic structures, three of which were typically not produced in isolation. We found that both single neuron activities and LFP were modulated by the production of each of the four call types. Moreover, the neural modulations in the frontal cortex showed distinct patterns for different call types, suggesting a representation of vocal signal features. In addition, we found that theta-band LFP oscillations were phase-locked to the phrases of twitter calls, which indicates the coordination of temporal structures of vocalizations. Our results suggested important functions of the marmoset frontal cortex in supporting the production of diverse vocalizations in vocal communication.