Hormonal and cardiac response of autistic children to changes in environmental stimulation.

A study was made of physiological responses of autistic children to variations in environmental load in order to examine the under- versus over-arousal dichotomy. More specifically, measures of urinary mucoprotein excretion and mean heart rate and three measures of heart rate variability were compared with matched controls in conditions of normal, high, and low total environmental load. The results suggest that, although behaviorally unresponsive, the autistic children responded physiologically, were generally in a lower state of arousal than the control group, and were labile in response to changes in stimulation.