Rearing experience differentially affects somatic and cardiac startle responses in rhesus monkeys (Macaca mulatta)

The present study reports, for the first time, somatic and cardiac responses to acoustic startle in 2 groups of rhesus monkeys (Macaca mulatta) with different rearing experiences. Both groups showed a significant direct relationship between startle amplitude and the intensity of the acoustic startle stimulus (80-120 dB) and rapid heart rate acceleration after a 120-dB stimulus. Monkeys reared with a same-age peer (PR) showed higher startle amplitudes than those reared with their mothers (MR), consistent with rearing effects in rodents. The MR monkeys, however, showed faster heart rate acceleration of greater overall magnitude than that of the PR group. The results are discussed with regard to a monkey model for neuropsychiatric disease.