Communication of Emotions in Animals☆

Emotional states enhance the organism's interaction with the environment, by prolonging certain internal states, amplifying experiences, and thus allowing for better evaluation of salient stimuli. Expressing emotional states or communicating them to other members of the species appeared to be highly adaptive. Emotional expression has evolved in animals over a long period of time and serves a number of biological functions, including locating and identifying, aiding in agonistic interactions, alarming, mobilizing, and recruiting other conspecifics or calming them down, as well as a number of affiliative functions promoting animal approach and group cohesiveness. Vocal communication is the most widespread and complex form of emotional expression in mammals. The laboratory rat has become the most-studied species with regard to the neural regulation of emission of vocalization and vocal expression of affective states. Two ascending tegmental neurotransmitter systems were identified as responsible for the initiation of two opposite affective states with emission of ultrasonic vocalizations concomitant to these states. The 22 kHz alarm vocalizations, which signal an aversive state, are initiated by the activation of the ascending cholinergic system, while the affiliative 50 kHz vocalizations, which signal an appetitive state, are initiated by activation of the mesolimbic dopamine system.