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 (n = 28), alexithymic people (n = 25), and non-autistic, non-alexithymic people (n = 55) participated in the study. Results showed that alexithymia and trait anxiety were reliable predictors of the magnitude of the placebo effect, but any effect of autism was weaker and unreliable. Results suggest that atypical interoception in alexithymia may explain differences previously thought to relate to autism.Lay AbstractPerception of pain can be altered by how one expects that pain to feel, producing well-known phenomena such as placebo effects. Placebo effects occur when a painful sensation is experienced as less painful than it otherwise would be, simply because we expect it to be less painful. Recently, researchers have suggested that the effect of expectation on how we perceive the world is different among the autistic population compared to non-autistic people. We therefore aimed to investigate whether this is the case for pain perception.We conducted a study where we were able to change people's expectations about how painful an electric shock would be, to see whether this would affect pain perception, and see whether the effect of expectations differs between autistic and non-autistic people. We were also interested in looking at the effect of alexithymia (difficulties in identifying and describing one's own emotions), which is suggested to affect pain perception and is prevalent in the autistic population.We found that alexithymia and anxiety predicted how susceptible someone was to the placebo effect (i.e., how much expecting a shock would not be painful affected one's pain perception). These effects were greater than any effect of autism, which was small and unreliable. This study adds to previous research which shows that many of the differences between autistic people and non-autistic people in terms of perceiving bodily sensations, including pain, may be better explained by alexithymia than autism.