Autism and psychosis as diametrical disorders of embodiment

Abstract

Humans have evolved an elaborate system of self-consciousness, self-identity, self-agency, and self-embodiment that is grounded in specific neurological structures including an expanded insula. Instantiation of the bodily self has been most-extensively studied via the 'rubber hand illusion', whereby parallel stimulation of a hidden true hand, and a viewed false hand, leads to the felt belief that the false hand is one's own. Autism and schizophrenia have both long been regarded as conditions centrally involving altered development of the self, but they have yet to be compared directly with regard to the self and embodiment. Here, we synthesize the embodied cognition literature for these and related conditions, and describe evidence that these two sets of disorders exhibit opposite susceptibilities from typical individuals to the rubber hand illusion: reduced on the autism spectrum and increased in schizophrenia and other psychotic-affective conditions. Moreover, the opposite illusion effects are mediated by a consilient set of associated phenomena, including empathy, interoception, anorexia risk and phenotypes, and patterns of genetic correlation. Taken together, these findings: (i) support the diametric model of autism and psychotic-affective disorders, (ii) implicate the adaptive human system of self-embodiment, and its neural bases, in neurodevelopmental disorders, and suggest new therapies and (iii) experimentally ground Bayesian predictive coding models with regard to autism compared with psychosis. Lay summary: Humans have evolved a highly developed sense of self and perception of one's own body. The 'rubber hand illusion' can be used to test individual variation in sense of self, relative to connection with others. We show that this illusion is reduced in autism spectrum disorders, and increased in psychotic and mood disorders. These findings have important implications for understanding and treatment of mental disorders.

Keywords: anorexia; autism; embodied cognition; interoception; predictive coding; rubber hand illusion; schizophrenia.

Figure 1.

The rubber hand illusion and its predictive-coding-based explanation

Figure 2.

Relationships of rubber hand illusion susceptibility with autism spectrum and psychotic-affective spectrum disorders, and relationships among relevant predictor variables. Negative relationship shown as ‘−’, positive relationship as ‘+’, and no difference as ‘0’. Citations: 1 and 2: (Table 1); 3: [89]; 4–7: (Table 1); 8: [88, 89]; 9–12: (Table 1); 13: [90]; 14 (see text); 15: (negative: [91–94]; [95] (one condition); [96]; no difference: [97]; [95] (one condition); [98]; [99]); 16: (positive: [100] (one condition); negative: [101, 102]). Borderline personality disorder (one study) [73] is discussed in the text; this conditions showed no difference from controls in interoceptive accuracy (one study [103])

Figure 3.

Framework, based in predictive coding, for interpretation of lower rubber hand illusion susceptibility in autism spectrum conditions, but higher susceptibility on the psychotic-affective spectrum. Drawing by Robert Fludd (1574–1637)