The effect of amygdala lesions on conditional and unconditional vocalizations in rats

Abstract

Electrolytic lesions centered on the amygdaloid central nucleus (ACe) resulted in the inability of rats to acquire a Pavlovian conditional vocalization response. Conditioning consisted of pairing a light conditional stimulus with a tailshock unconditional stimulus (US). The thresholds of three unconditional responses (URs) to tailshock were assessed prior to conditioning. These URs are organized at spinal (spinal motor reflexes), medullary (vocalizations during shock), and forebrain (vocalization afterdischarges, VADs) levels of the neuraxis. Compared to sham-lesioned controls, rats with amygdala lesions exhibited a selective elevation in the threshold of VADs. During conditioning the amplitude and duration of VADs were selectively reduced in amygdala-lesioned rats. These findings support earlier observations of that elicitation of VADs by tailshock correlates with the capacity of this US to support fear conditioning. The ACe may be involved in both associative and non-associative aspects of fear conditioning, but for progress in our understanding it is essential to evaluate its role in the generation of conditioning relevant URs.