Altered processing of self-produced sensations in psychosis at cortical and spinal levels.

Psychosis is often characterized by disturbances in the sense of self, with patients frequently misattributing self-produced sensations to external sources. While somatic hallucinations and misperceptions are common, the underlying disruptions in basic bodily self-processing remain unclear. We aimed to investigate processing of self-evoked sensations, including touch and interoception, in psychosis using a multimodal, multi-method approach. This case-control-study included a total of 70 participants (35 patients diagnosed with psychotic disorders, 35 age- and sex-matched controls). Participants performed self-/other-touch-tasks and interoceptive assessments during functional MRI, evoked potentials measurements, and/or behavioral and psychophysical tests. Primary outcomes included neural and behavioral responses to self- and externally-generated sensations (touch and heartbeat). Brain activation, spinal evoked responses, heartbeat perception and processing (evoked responses), and behavioral measures were analyzed, with preregistered hypotheses. Patients demonstrated heightened right superior temporal gyrus activation during self-touch. Tactile self-other distinction impairments were evident at the spinal cord level. Behaviorally, patients showed reduced differentiation in tactile thresholds for self- vs. other-touch. Interoceptive impairments included diminished cortical responses to heartbeat signals, lower interoceptive accuracy (heartbeat detection), and reduced self-reported interoceptive sensitivity. These findings reveal pervasive sensory and self-related disturbances in psychotic disorders. Impairments in differentiating self- and externally-evoked responses, detectable as early as the spinal cord level, may contribute to higher-order symptoms of psychosis.