A new Tel Aviv University (TAU) study has found that people with autism experience pain at a higher intensity than the general population and are less adaptable to the sensation. This finding is contrary to the prevalent belief that people with autism are  “indifferent to pain.” The researchers expressed the hope that the findings of their study will lead to more appropriate treatment on the part of medical staff, caregivers, and parents toward people with autism, who do not always express the experience of pain in the usual way.

The study was led by Dr. Tami Bar-Shalita of TAU’s Sackler Faculty of Medicine, who initiated the study; Dr. Yelena Granovsky of the Technion and Rambam Medical Center; and Professor Irit Weissman-Fogel and Professor Eynat Gal of the University of Haifa. The study constitutes a framework for the theses of PhD students Tzeela Hofmann and Mary Klingel-Levy. The research was published on August 26, 2022, in the journal PAIN.

“Approximately 10% of the general population suffer from sensory modulation dysfunction, which is a sensory hypersensitivity at a level that compromises normal daily functioning and quality of life,” Dr. Bar-Shalita explains. “These people have difficulty, for example, ignoring or adapting to buzzing or flickering of fluorescent lights, humming of air conditioners or fans, or the crunching of popcorn by someone sitting next to them in the cinema.

“In previous laboratory studies, we found that these people suffer from pain more than those without sensory modulation dysfunction. Since it is known that sensory modulation dysfunction occurs in people with autism at a rate of 70-90%, it constitutes a criterion for diagnosing autism and is associated with its severity. We were interested in exploring pain perception in autism, so we asked: Do people with autism hurt more than the general population? This question was hardly studied in the lab before we got started.”

According to the researchers, for many years the prevalent opinion was that people with autism suffered less from pain or that they were indifferent to the sensation. Indeed, “indifference to pain” is one of the characteristics presented in the current diagnostic criteria of autism. The proof of this was, supposedly, their tendency to inflict pain on themselves by self-harm.

“This assumption is not necessarily true,” Dr. Bar-Shalita says “We know that self-harm could stem from attempts to suppress pain, and it could be that they hurt themselves in order to activate, unconsciously, a physical mechanism of ‘pain inhibiting pain.'”

This study was approved by the ethics committee of the associated academic institutions and Rambam Medical Center. The study included 52 adults with high-functioning autism (HFA) and normal intelligence, hitherto the largest reported sample in the world in studies on pain among people with autism. The study made use of psychophysical tests to evaluate pain, commonly used in the area of pain study. These methods examine the link between stimulus and response as the researcher, using a computer, controls the duration and intensity of stimulus and examinees are asked to rank the intensity of the pain felt by them on a scale of 0 to 100.

The findings have proven beyond doubt that people with autism hurt more, the researchers say, and that their pain suppression mechanism is less effective.

The researchers conducted a variety of measurements, aimed among other things at examining whether the hypersensitivity to pain derives from a sensitized nervous system or from suppression of mechanisms that are supposed to enable adjustment and, over time, reduce the response to the stimulus. They found that in the case of people with autism, it is a combination of the two: an increase of the pain signal along with a less effective pain inhibition mechanism.

“Our study constituted a comprehensive, in-depth study of the intensity of pain experienced by people with autism,” Dr. Bar-Shalita concludes. “The prevalent belief was that they are supposedly ‘indifferent to pain,’ and there are reports that medical and other professional staff treated them accordingly.

“The results of our study indicate that, in most cases, the sensitivity to pain of people with autism is actually higher than that of most of the population. At the same time, they are unsuccessful at effectively suppressing painful stimuli. We hope that our findings will benefit the professionals and practitioners handling this population and contribute to the advancement of personalized treatment.”

The research was funded by the Israel Science Foundation (ISF).