A Reliable Effect of Alexithymia, but Not Autism, on Placebo Hypoalgesia.

Perception of pain can be altered by one's expectations of that pain, producing well-known phenomena such as placebo effects. It has been suggested that perceptual inference functions differently in autism, with perception weighted towards bottom-up sensory evidence rather than top-down expectations. This account would predict reduced placebo effects in autism. However, research also indicates that atypical interoception (perception of bodily sensations) in autism may be better explained by co-occurring alexithymia. This latter finding suggests that any differences in perceptual inference in autism, at least within the interoceptive domain, may be a product of co-occurring alexithymia. We conducted a study in London and Oxford, England, using a placebo hypoalgesia paradigm to assess perceptual inferences in autism and alexithymia. This paradigm permits manipulation of expectations (concerning the magnitude of pain relief) while measuring individual differences in the perception of stimuli (perceived pain). We investigated whether the magnitude of the placebo effect could be explained by autistic and/or alexithymic traits. Ninety-six adults, including autistic people (