Basal Sympathetic Nervous System Functioning in Autism: A Systematic Review of Neurochemical Studies.
Autism shows normal resting sympathetic chemistry except for higher plasma epinephrine, so target acute stress moments, not chronic arousal.
01Research in Context
What this study did
Neupane et al. (2025) pooled all papers that measured resting adrenaline, noradrenaline and dopamine in people with autism. They hunted for group differences at baseline, not during stress or tasks.
The team followed PRISMA rules and graded each study for quality. They compared blood and urine levels between autistic and non-autistic participants.
What they found
Only plasma epinephrine was higher in the autism group. Every other sympathetic chemical looked the same at rest.
The authors say this points to sharper stress reactions, not a constantly 'revved-up' nervous system.
How this fits with other research
Kunz et al. (1982) once guessed that autism might ride on chronic monoamine overload. The new review updates and partly overturns that old view — basal levels are mostly normal.
Işeri et al. (2011) also found a single blood marker high in autism (EGF), but could not link it to behavior. Krisha et al. echo this pattern: the epinephrine bump is real, yet its clinical meaning is still unclear.
Iosa et al. (2012) saw higher resting blood flow in limbic brain areas, while Krisha et al. show normal resting catecholamines. Together they hint that upstream brain regulation, not peripheral chemistry, drives the flow change.
Why it matters
For BCBAs, the null basal findings mean you can stop assuming clients live in daily 'fight-or-flight.' Instead, watch for sudden spikes during transitions or sensory events. Pair brief physiological checks — heart-rate or hand-temperature — with your ABC data. If you see a jump, teach coping skills right then, not all day long.
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02At a glance
03Original abstract
PURPOSE: Sympathetic nervous system (SNS) functioning in autism is of interest etiologically and clinically. It remains unclear whether there is a chronic state of hyperarousal or a heightened physiological response to stressful situations, or both, in autism (ASD). A systematic review of neurochemical studies of SNS functioning in ASD addressed these issues. METHODS: The PubMed, Scopus, Ovid, and Web of Science databases were searched using a first set of search terms consisting of norepinephrine (NE), epinephrine (EPI) and their known metabolites. A second set of terms consisted of relevant diagnostic terms. The sets were combined, and the retrieved studies were screened by three independent reviewers. RESULTS: With one exception, there were no significant differences between groups for the urine measures and for all plasma metabolite measures. However, plasma EPI showed a significant elevation in the ASD group and plasma NE showed a trend level increase. The reported variances were similar in the two groups, and typical nighttime decreases in sympathetic measures were reported in ASD groups. CONCLUSIONS: The results indicate that mean basal SNS functioning is not increased in ASD. In contrast, the plasma EPI and NE findings are consistent with increased reactivity to acute stressors in ASD. There was no indication of an admixture of hyper- and hypo-arousal subgroups and typical nighttime sympathetic diminution was seen in ASD. It appears that sympathetic functioning is not atypical in ASD and that the apparent heightened reactivity to stress is more likely due to increased elicitation of the sympathetic system in ASD.
Journal of autism and developmental disorders, 2025 · doi:10.1007/BF02408428