Neural mechanisms of animal vocalization and communication

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The program of research concerns vocal communication in rats. Vocalizations are used as a measuring tool allowing us to study brain mechanisms of emotional states. Rats communicate by ultrasonic calls, which are beyond the hearing range of humans. However, their calls are produced and controlled by similar (homologue) brain structures to those in the human brain that are involved in emotional arousal and vocal expression of our emotional states. The proposed research is focused on two transmitter systems (dopaminergic and cholinergic) originating from the brain stem (tegmentum) and innervating structures generating emotional arousal and emission of vocalizations that carry messages to other rats. Activity of the dopaminergic system initiates an appetitive (pleasant) state with emission of 50 kHz calls, while activity of the cholinergic system initiates an aversive (unpleasant) state with emission of 22 kHz calls. These vocalizations carry messages addressed to other rats and are used in research as a measure of the activity of relevant brain systems and the resulting state of the organism. The proposal includes investigation of the interaction between the dopaminergic and cholinergic systems and the mechanisms allowing the brain to select and initiate either the appetitive or aversive state, but not both of them together. The project also includes studies of other brain systems (in the hypothalamus) controlling emotive states. Messages coded in the vocalizations (semiotic content), as well as their development from infancy to adulthood, will also be studied, along with the development of the dopaminergic and cholinergic transmitter systems throughout the same ages.