LESIONS OF THE AMYGDALA DO NOT AFFECT THE ENHANCEMENT OF THE ACOUSTICSTARTLE RESPONSE BY BACKGROUND-NOISE

The acoustic startle response (ASR) is enhanced in the presence of lou d background noise. We examined whether or not this increase of respon se strength is mediated by the amygdala, which is known to be involved in various phenomena of enhancement of the ASR. To achieve this aim, we tested whether or not amygdaloid lesions with the excitotoxin N-met hyl-D-aspartate (NMDA) would abolish the enhancement of the ASR by bac kground noise in 13 Wistar rats. Loss of foot-shock sensitization in t hese rats, as well as histological evaluation, proved the successful d estruction of the amygdala. However, the enhancement by background noi se of the ASR, which was observed in sham-operated controls, was not a ffected in amygdala-lesioned rats. Therefore, we conclude that the bac kground noise facilitation does not involve emotional components that are mediated by the amygdala. On the basis of these findings, we diffe rentiate between the startle-enhancing effect of background noise and the amygdala-mediated effect of foot shocks on the ASR. Copyright (C) 1996 Elsevier Science Inc.