AUTONOMIC RESPONSE TO AUDITORY-STIMULATION

Autonomic and behavioral response to fear stimulation (sudden noise 80 dB) was studied in 12 sleeping infants at ages 8-50 weeks. The aim of the present study was to identify a possible passive defense response in infants. The response, which is widespread in birds and mammals, i s characterized by apnea and bradycardia with circulatory changes as s een during the forced diving response. Upon stimulation, two respirato ry responses were elicited: apnea preceded by irregular respiration or simple irregular respiration. Apnea was elicited in 58% of stimulatio ns at ages 8-16 weeks compared to 14% at 28-50 weeks. The mean duratio n of apnea decreased from 7.8 s (+/- 1.8 s) at 8-13 weeks to 4.7 s (+/ - 1.1 s) at 17-20 weeks. The preceding irregular respiration increased from 5.3 s (+/- 4.4 s) to 10.6 s (+/- 5.4 s) at the same ages. The he art rate response was biphasic and were interpreted as the orienting r esponse. The mean deceleration in relation to apnea was 16% at 8-16 we eks and was reduced to 8% at 28-50 weeks. Infants of smoking mothers w ere more prone to respond with apnea than infants of non-smoking mothe rs (73% versus 38%). REM sleep and long postprandial sleep time increa sed the probability of apnea response (62% versus 38% and 66% versus 3 5%). The responses seen may be interpreted as expressions of the passi ve defense response.