Ego-boundary disturbance (EBD) in schizophrenia is a unique psychopathological cluster characterized by passivity experiences (involving thoughts, actions, emotions and sensations) attributed by patients to some external agency. Aberrant mirror neuron activation may explain impaired self-monitoring and agency attribution underlying these ‘first rank’ symptoms.

We aim to study mirror neuron activity (MNA) in schizophrenia patients with and without EBD using transcranial magnetic stimulation (TMS).

50 right-handed schizophrenia patients (DSM IV) were evaluated using the Mini-International Neuropsychiatric Interview and the Positive & Negative Syndrome Scale. They completed a TMS experiment to assess putative premotor MNA. Motor evoked potential (MEP) was recorded in the right first dorsal interosseous muscle (FDI) with (a) 120% of resting motor threshold (RMT) and (b) stimulus intensity set to evoke MEP of 1 millivolt amplitude (MT1). These were done in 3 states: actual observation of an action using the FDI, virtual-observation (video) of this action and resting state. The difference of MEP between resting to action-observation states formed the measure of MNA.

MNA measured using MT1 and 120% RMT paradigms for real-observation was significantly lower in the 18 patients with EBD (thought-broadcast/withdrawal/insertion, made-act/impulse/affect and somatic passivity) than the 32 patients without EBD (t=2.75, p = 0.009; t = 2.41, p = 0.02 respectively for the two paradigms). The two groups did not differ on age, gender, education and total symptom scores.

Schizophrenia patients with EBD have lower premotor MNA. This highlights the role of MNA dysfunction in the pathophysiology of this unique and intriguing symptom cluster in schizophrenia.