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<p>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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