Cerebral basis for positive psychosis symptoms pinpointed

By Eleanor McDermid, Senior medwireNews Reporter

Altered activation in the secondary somatosensory cortex (SII) during sensorimotor experiences may underlie the flawed judgments resulting in positive schizophrenia symptoms, research suggests.

This change may result in patients with schizophrenia misattributing the consequences of their own actions to external forces, explain study authors Sukhwinder Shergill (King’s College London, UK) and colleagues.

“These findings provide a cerebral basis for the increasing body of behavioral evidence that suggests that impaired motor prediction leads to a set of symptoms of schizophrenia explicable by a fundamental misjudgment of agency,” they write in JAMA Psychiatry.

The team recruited 19 patients with schizophrenia and 19 mentally healthy controls to take part in a sensorimotor experiment in which the sensation of a tap with the right index finger was transmitted via a torque motor to the left index finger, either synchronously, with an unexpected delay, or in the absence of action from the right finger.

Functional magnetic resonance imaging showed that control participants had significant clusters of activation in the bilateral SII during the task, but that this activation was attenuated if the action and sensation occurred synchronously, ie, the participants believed that their own actions caused the sensation.

By contrast, SII activation in schizophrenia patients was similar regardless of whether the sensation appeared to be linked to their own actions.

“Unlike healthy individuals, individuals with schizophrenia do not attenuate predictable sensory signals, suggesting that they are unable to predict the sensory consequences of their own actions,” say the researchers.

“Although comparably reduced attenuation has been previously reported in the verbal domain, this work finds for the first time, to our knowledge, that this physiologic deficit is exhibited more generally.”

The failure of schizophrenia patients to attenuate SII activation was associated with the severity of positive symptoms. Specifically, the degree of attenuation decreased in line with increasing hallucination score on the Positive and Negative Syndrome Scale.

Shergill et al note, however, that the effect is unlikely to be specific to hallucinations, with this being just one potential consequence of the underlying defect.

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