THE ROLE OF THE PREFRONTAL CORTEX IN SELF-CONSCIOUSNESS - THE CASE OFAUDITORY HALLUCINATIONS

Many patients with schizophrenia report hallucinations in which they h ear voices talking to them or about them. Behavioural and physiologica l studies show that this experience is associated with processes occur ring in auditory language systems associated with both the production and the reception of speech. I propose that hallucinations are experie nced because patients have difficulty in distinguishing sensations cau sed by their own actions from those that arise from external influence s. This distinction can be made by predicting the sensations that will result from executive commands (forward modelling). If the predicted sensation matches the actual sensation then no outside influences have occurred and perception of change can be 'cancelled'. At the physiolo gical level this mechanism depends upon interactions between the prefr ontal areas where the executive commands originate and posterior brain regions concerned with the resultant sensations. Evidence from functi onal brain imaging confirms that interactions between prefrontal (exec utive) areas and auditory association areas are abnormal in schizophre nia. However, this account needs to be extended before we can understa nd why patients experience the voices as emanating, not just from an e xternal source, but from agents who are trying to influence their beha viour. Recent imaging studies suggest that medial prefrontal cortex is engaged when we think about other people, but the precise nature of t he interaction of this brain area with other regions remains to be est ablished.