Explaining the symptoms of schizophrenia: abnormalities in the awareness of action.

We propose that the primary cognitive deficit associated with delusions of control is a lack of awareness of certain aspects of motor control. This problem arises because of a failure in the mechanism by which the predicted consequences of an action are derived from a forward model based on the intended sequence of motor commands. This problem leads to a number of behavioural consequences, such as a lack of central error correction, many of which have been observed in patients with delusions of control and related symptoms. At the physiological level, delusions of control are associated with over-activity in parietal cortex. We suggest that this over-activity results from a failure to attenuate responses to sensations of limb movements even though these sensations can be anticipated on the basis of the movements intended. The lack of attenuation may arise from long range cortico-cortical disconnections which prevent inhibitory signals arising in the frontal areas which generate motor commands from reaching the appropriate sensory areas.