Hyper- or Hypo-arousal?
Hyper-arousal is not universally accepted by all researchers. A recent review of sensory difficulties in autism concluded that the experimental evidence or hyper-arousal was at best mixed. There are a number of problems with this view. First, ASD is a heterogeneous condition and the assumption that hyper-arousal should be a general explanatory theory of autism was too broad. Second, sensitivity to arousing stimuli may be intermittently presenting in individuals with ASD. Third, the stimuli employed in habituation paradigms cannot easily mimic real life non-laboratory-based events. Animal research on arousal has attempted to link deficiencies to conditions such as attention-deficit hyperactivity disorder, Alzheimer's disease, and autism.
Historically, hypo-arousal in people with an ASD has also been proposed as a factor to specific stimuli, although with limited laboratory evidence. Repetitive movements may serve a dearousing function. Unusual sensory experiences have been reported in autobiographical accounts of people with an ASD. Sensory over-activity has been explained as a possible response to hyper-arousal. An understanding of arousal and sensory experiences may have great explanatory significance for some forms of challenging behaviours.