Habituation of the infant arousal response

Study Objectives-Arousal is considered to be an important protective respon se in a sleeping infant and its depression could leave an infant vulnerable to a life threatening stimulus. We found previously that arousal to a non- respiratory (tactile) stimulus occurs in a sequence of events that begins w ith spinal, followed by brainstem responses, and then a cortical electroenc ephalographic (EEG) arousal response. We hypothesized that repeated stimuli would depress the arousal responses by habituation and that spinal and bra instem responses would be more resistant to habituation than cortical respo nses. Participants-We studied 22 normal infants. interventions-The infants underwent polysomnographic monitoring during a daytime nap. Tactile stimuli was applied to the infants foot at 5-second intervals. Measurements and Re sults-We found that spinal, brainstem, and cortical responses occurred on t he first trial of each test. Repealed trials during non-rapid eye movement (NREM) and rapid eye movement (REM) sleep resulted in a decrease in the inc idence of each individual response and eventually elimination of the arousa l responses. Cortical responses were eliminated first, followed by brainste m responses and finally spinal responses. The elimination of each of the re sponses occurred more rapidly during REM sleep than during NREM sleep. Conc lusions-Habituation of the infant arousal sequence occurs with repeated tac tile stimulation. There is a serial habituation of responses from the corti cal to the spinal level, which occurs more rapidly during REM sleep. Rapid habituation to innocuous stimuli is probably beneficial in avoiding detrime ntal sleep disruptions. However, in situations requiring the protective fun ctions of arousal, such habituation could be detrimental to an infant.