Paradoxical autonomic response to mental tasks in autism.

Autonomic responses to mental tasks requiring sustained attention were examined in individuals with autism and age- and ability-matched controls. Cardiac autonomic function (CAF) was evaluated based on heart rate variability. While the control group showed a significant decrease in the parasympathetic function during mental tasks, the autistic group showed no significant changes in CAF. When examined individually, parasympathetic function was suppressed in all subjects in the control group. On the other hand, parasympathetic function was activated in half of the autistic subjects. The paradoxical autonomic response suggests that some autistic subjects were more stressed under 'resting' conditions than while performing mechanical or repetitive mental tasks. The results seem to support autonomic hyperarousal in some people with autism.