Are Sensory Problems in ASD Really Sensory?

Background: Abnormal sensory responses are a commonly reported clinical feature of autism spectrum disorder (ASD). Sensory symptoms are assessed by a number of standardized questionnaires; studies based on these second-hand, self- or observational reports find increased rates of sensation seeking and/or sensation avoidance in all sensory modalities in ASD. Despite the general consensus that abnormal sensory function is an important clinical feature of autism, there is little or no understanding of the underlying mechanisms. Further, because the vast majority of evidence regarding these symptoms is based solely on behavioral descriptions, it is not clear if these symptoms are truly sensory in nature or if alternatively, they reflect abnormalities in general arousal or attention. Because our previous work suggests that abnormal sensory processing in ASD may be driven by impaired control of attention and arousal, we suggest that what appears to be abnormal sensory function in ASD may result from interactions of attention and arousal with sensory processing.

Objectives: Our goal was to investigate underlying sources of sensory symptoms by assessing critical components of sensory processing (e.g., sensory habituation and neural refraction) and the influence of attention and physiological arousal on sensory responsiveness.

Methods: Study participants were adults with ASD and a typically developing (TD) adult comparison group. Participants completed three experiments utilizing behavioral, event-related brain potential (ERP) and heart-rate (HR & HRV) measures to examine neural sensory responses to: auditory stimulation; changes in intensity of auditory stimulation; repeated auditory stimulation (refractory and habituation responses). During these experiments, we also examined the effects of physiological arousal and attention on brain responses to sensory stimulation. 

Results: Adults with ASD reported significant sensory problems on the Sensory Profile Questionnaire (Brown & Dunn, 2002), suggesting that sensory difficulties persist throughout the lifespan. Physiological measures, however, did not support a true sensory origin of these symptoms. ERP responses to auditory stimuli of varying intensity were similar in amplitude between ASD and TD groups. Also, ASD adults, like TD adults showed the expected refractory response to a repeated sensory stimulus (i.e., the sensory response to the second of a pair of stimuli was smaller).  However, gradual habituation over time was atypical in ASD, but only when sensory stimulation was unattended. That is, response to irrelevant background sounds did not diminish over time in ASD adults; in TD adults there was little sensory response to these repeated background stimuli after only several minutes. Additionally, baseline arousal differed between groups as measured by HR & HRV, and greater arousal was observed in the ASD group during the presentation of auditory tones.

Conclusions: These findings suggest that in adults with ASD, sensory difficulties that are experienced in daily life may be a function of differences in the modulation of general arousal and the effects of attentional state rather than abnormalities in basic sensory response. Understanding the nature of sensory abnormalities and the processing level (sensory, arousal, attention) at which sensory behavior is perturbed can guide development of more specific treatment of these troublesome symptoms.