Interoceptive Impairments Do Not Lie at the Heart of Autism or Alexithymia

Background: Background: Quattrocki and Friston (2012) argued that abnormalities in interoception–the process of bringing internal physiological states to awareness–could lie at the heart of autism, because of the critical role interoception plays in the ontogeny of social-affective processes. This proposal drew criticism from proponents of the alexithymia hypothesis, who argue that social-affective and underlying interoceptive impairments are not a feature of autism per se, but of alexithymia (a condition characterised by difficulties describing and identifying one's own emotions), which commonly co-occurs with autism. Despite the importance of this debate, direct empirical evidence is scarce and inconsistent.

Objectives: To test competing theories of autism (and self-awareness in this disorder).

Methods: Experiment 1 examined in a sample of 137 neurotypical individuals the association among autistic traits (measured using the Autism-spectrum Quotient; AQ), alexithymia (measured using the TAS-20), and interoceptive accuracy (using a standard heartbeat tracking measure). The heartbeat tracking measure required participants to close their eyes and, without taking their pulse, silently count their heartbeat during four different time intervals (25, 35, 45 and 100 sec). A pulse oximeter attached to participants’ index finger measured actual heart rate. The closer the estimated heartbeats to the actual number of heartbeats during each interval, the better the interoceptive accuracy. In Experiment 2, interoceptive accuracy was assessed in 46 adults with ASD (27 of whom had clinically-significant alexithymia) and 48 neurotypical adults. Bayesian analyses were employed to complement null hypothesis significance testing (BF₁₀ < 1 = evidence for the null; BF₁₀ > 3 = evidence for the alternative hypothesis).

Results: Experiment 1 confirmed strong associations between autistic traits and alexithymia (r = .42, p <.001, BF₁₀ > 100), but yielded no evidence to suggest that either was associated with interoceptive difficulties (rs < -.11, ps > .22, BF₁₀ < 0.22). Those participants with scores above the cut-off alexithymia on the TAS-20 were assigned to a “high alexithymia” group (n = 30) and those with scores below the cut-off to a “low alexithymia” group (n = 107). There were no significant differences between these two groups in terms of levels or patterns of performance on the heartbeat tracking task, contrary to the alexithymia hypothesis (ps > .30, ds < 0.22, BF₁₀ < 0.35). Reliability of all findings was confirmed by randomly splitting the total sample into two groups of n = 68 and 69 participants and re-analysing the data in each sub-sample. Results were identical in each subsample and always supported the null. Similarly, Experiment 2 provided no evidence for interoceptive impairments in autistic adults ( p = .53, d = 0.13, BF₁₀ = 0.26), and neither was interoceptive accuracy associated with either AQ (or ADOS) score or TAS-20 score in either diagnostic group.

Conclusions: The observations pose a significant challenge to notions that interoceptive impairments constitute a core feature of either ASD or alexithymia, at least as far as the direct perception of interoceptive signals is concerned. Instead, they support the theory that detection of physical states is undiminished in ASD.