C. Frith, THE ROLE OF THE PREFRONTAL CORTEX IN SELF-CONSCIOUSNESS - THE CASE OFAUDITORY HALLUCINATIONS, Philosophical transactions-Royal Society of London. Biological sciences, 351(1346), 1996, pp. 1505-1512
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.