Arousal and Autistic Spectrum Disorder (ASD)

Arousal is a physiological and psychological state of being awake or reactive to stimuli. It involves the activation of the reticular activating system in the brain stem, the autonomic nervous system and the endocrine system, leading to increased heart rate and blood pressure and a condition of sensory alertness, mobility and readiness to respond. There are many different neural systems involved in what is collectively known as the arousal system. Four major systems originating in the brainstem, with connections extending throughout the cortex, are based on the brain's neurotransmitters, acetylcholine, norepinephrine, dopamine, and serotonin. When these systems are in action, the receiving neural areas become sensitive and responsive to incoming signals. Arousal is not a new construct and was originally proposed as an explanatory theory for autism spectrum disorders. Two implications of this theory are that children and adults with an autism spectrum disorder (ASD) would be more reactive to sensory stimuli than the normal population, and they may be slower to habituate to stimuli. There is some laboratory evidence of differences in physiological responses of individuals with ASD compared to non-autistic controls.