Separable brainstem and forebrain contributions to ultrasonic vocalizations in infant rats

Competing views persist concerning the functional significance of ultrasonic vocalizations (USVs) emitted by infant rats. One perspective holds that USVs result from an emotional state of fear and anxiety, the adult expression of which depends in part on forebrain mechanisms. Here the authors examine whether pups lacking forebrain input are capable of emitting USVs. Aspirations of neocortex and hippocampus or precollicular decerebrations were performed on 8-day-old rats. After the rats recovered, USV responses were recorded for 10 min at room temperature (Phase 1) followed by enhanced cooling for 20 min (Phase 2). Experimental pups emitted significantly fewer USVs than shams during Phase 1 but vocalized at similar rates during Phase 2. Thus, in infants, brainstem neural circuitry is sufficient to support emission of USVs.