Background: Phase synchronization of neural activity preceding a motor act may reflect an efference copy of the motor plan and its expected sensory consequences (corollary discharge), which is sent to sensory cortex to herald the arrival of self-generated sensations and dampen the resulting sensory experience. We performed time-frequency decomposition of response-locked electroencephalogram (EEG) to examine phase synchronization of oscillations across trials (phase-locking factor [PLF]) to self-paced button presses. If prepress PLF reflects the activity in motor cortex, it should be contralateralized. If it reflects the action of the efference copy, it should be related to subsequent sensory suppression. If efference copy/corollary discharge mechanisms are abnormal in schizophrenia, it should be reduced in patients with schizophrenia.
Methods: Electroencephalogram was collected while 23 patients (20 schizophrenia; 3 schizoaffective) and 25 age-matched control subjects pressed a button, at will, every 1 to 2 sec. Phase-locking factor preceding and following button presses was calculated from single-trial EEG; averaging single trials yielded response-locked event-related potentials (ERPs) to the tactile response associated with button pressing.
Results: Consistent with its hypothesized reflection of efference copy/corollary discharge signals, prepress gamma band neural synchrony was 1) maximal over the contralateral sensory-motor cortex in healthy subjects, 2) correlated with the ipsilateralized somatosensory ERP amplitude evoked by the press, and 3) reduced in patients. Prepress neural synchrony in the beta band was also reduced in patients, especially those with avolition/apathy.
Conclusions: These data are consistent with dysfunction of forward model circuitry in schizophrenia and suggest that the specific motor-sensory system affected is selectively linked to symptoms involving that system.