A Window Into Autonomic Nervous System Functioning in Autism: Pupillometry in Adults on the Autism Spectrum
The autonomic nervous system (ANS) regulates physiological processes throughout the body and disruption or imbalance of that system has been associated with negative physical and psychological outcomes. Pupil responsivity is controlled by the autonomic nervous system and has been show to index activity of the locus coeruleus-norepinephrine (LC-NE) pathway of innervation. Dysregulation of that pathway has been proposed to relate to differences in attentional control in autism. The current study looked at autonomic nervous system functioning in adults on the autism spectrum through the lens of pupil responsivity to tasks probing reactions to changes in environmental lighting and to complex stimuli. The primary aims of the study evaluated the questions: (1) Do measures of pupil response to different types of stimuli yield different results based on autism diagnostic status? and (2) Are there relationships between measures of pupil response, features of autism and self-reported symptoms of depression and anxiety? Pupillometry and symptom measures were conducted with a sample of adults on the autism spectrum (N=11) and adults without a diagnosis of autism (N=14). Primary variables were baseline pupil diameter, amplitude of dilation/constriction, latency to reach maximal dilation/constriction and recovery velocity. Regarding pupil response to environmental lighting, results indicated timing differences of pupillary response over both light and dark conditions based on autism diagnostic status. In particular, adults on the autism spectrum showed longer latency of pupil response to flashes of dark after being accustomed to a light and slower recovery to the accustomed dark condition after being exposed to flashes of light. Regarding tasks evoking pupil responses to complex stimuli (an auditory reversal learning task and an auditory oddball task), results indicated magnitude of response (amplitude) and variability of response differences related to autism diagnostic status. In particular, adults on the autism spectrum showed larger amplitude of response to all trials in the reversal learning task and greater variability of baseline pupil size across trials in the auditory oddball task than adults without a diagnosis of autism. Across tasks evoking pupil response related to environmental lighting or complex stimuli, associations between autism traits—in particular, intense interests/repetitive behaviors, depression, and anxiety—and different pupillometry measures were found in both the autism and non-autism groups. However, these relationships were different for the different groups. The current study explores differences in pupillary light reflex in adults on the autism spectrum and the results support extant findings of individuals on the autism spectrum potentially having an alternate time course of pupil response. The implications these results may have in terms of understanding of ANS functioning, particularly different sympathetic engagement of the LC-NE pathway and differences in attentional control or reward sensitivity, in autism are discussed. Results also suggest that certain features of autism as well as depression and anxiety seem to co-vary with differences in certain pupillometry measure—especially in the context of increased cognitive demands. Limitations of the study, including sample size and measurement issues, are discussed. Overall, the results suggest future research directions, which may increase understanding of relationships between individual behavior and brain functioning across the autism spectrum. These include possible comparisons of pupil response measures to other direct measures of ANS or brain function as well as the need for controlling for additional measures of psychological well-being and reward sensitivity.
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