Abstract
BackgroundDelusions and hallucinations are classic positive symptoms of schizophrenia. A contemporary cognitive theory called the ‘forward output model’ suggests that the misattribution of self-generated actions may underlie some of these types of symptoms, such as delusions of control – the experience of self-generated action being controlled by an external agency. In order to examine the validity of this suggestion, we performed a longitudinal functional magnetic resonance imaging (fMRI) study examining neuronal activation associated with motor movement during acute psychosis.MethodsWe studied brain activation using fMRI during a motor task in 11 patients with schizophrenia and 9 healthy controls. The patient group was tested at two time points separated by 6–8 weeks.ResultsAt initial testing, the patient group had a mean Positive and Negative Syndrome Scale score of 56.3, and showed significantly increased activation within the left inferior parietal lobe (IPL) compared to controls. Patients reported significantly decreased positive symptoms at 6–8 week followup and IPL activation had returned to normal. Our results demonstrate that first-rank positive symptoms are associated with hyperactivation in the secondary somatosensory cortex (IPL).ConclusionsThese findings lend further credence to the theory that a dysfunction in the sensory feedback system located in the IPL, and which is thought to underlie our sense of agency, may contribute to the aetiology of delusions of control.
Highlights
Delusions and hallucinations are classic positive symptoms of schizophrenia
Our findings further demonstrate that inferior parietal lobe (IPL) hyperactivation is systematically found in patients with positive symptoms of psychosis while performing motor activity
Our findings indicate that psychotic symptoms may not be associated with right IPL hyperaction during motor tasks, but that the hemispherical location may be more complex
Summary
Delusions and hallucinations are classic positive symptoms of schizophrenia. A contemporary cognitive theory called the ‘forward output model’ suggests that the misattribution of self-generated actions may underlie some of these types of symptoms, such as delusions of control – the experience of self-generated action being controlled by an external agency. In the case of delusions of control, for example, which refer to the misattribution of selfgenerated activity to an external source or agency, this dysfunction is thought to arise in the mechanisms underlying self-generated action. The efference copy is used in conjunction with an internally represented causal model linking actions to their sensory outcomes to give a prediction of the sensory consequences of our actions [1]. According to this model, patients with delusions of control fail to integrate the intention to act with the perception of their action, and do not consider themselves as the originator. A dysfunction in our internal model has the consequence of the action being assigned to an external agency; the belief being that someone else has caused their movement
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