THE ROLE OF THE PREFRONTAL CORTEX IN HIGHER COGNITIVE FUNCTIONS

The higher cognitive functions, working memory, mental imagery and wil led action, are all intimately associated with consciousness. The comm on process underlying all these functions is that information is ''hel d in mind'' for a period of time. This information, which may be about stimuli or responses, can be derived front the past or generated for the future. Brain imaging studies show that ''holding something in min d'' is associated with activity in an extended system which involves b oth prefrontal cortex and more posterior areas whose location is deter mined by the nature of the information being held in mind. Automatic a ctions and perceptions which do not involve consciousness are associat ed with activity in the relevant posterior areas, but not in the prefr ontal cortex. These studies demonstrate that activity occurs in the sa me posterior area whether the associated information comes from the ou tside world or is internally generated. This raises the problem of how we know whether our experience derives from mental imagery or from so mething happening in the outside world. There is evidence that patient s with schizophrenia have precisely this problem since they perceive t heir own thoughts and even sub-vocal speech as coming from outside (ha llucinations). Recent brain imaging studies suggest that there is a di sconnection between prefrontal and posterior areas in these patients w hich could explain their characteristic misperceptions.