Introduction

Historical and contemporary accounts of focal lesions affecting the frontal lobe have emphasized significant changes in personality and behavior but often minimal findings on clinical neurological, neuropsychological, and psychiatric examinations. Diagnosis and management of frontal lobe syndromes, particularly those involving the prefrontal cortex, encompass an unusually broad range of signs and symptoms. The underlying mechanisms of these syndromes are not yet clear, due to the complex organizational features of prefrontal cortex as well as its mediation of a broad range of variation in human adaptive behavior.

Neuropsychological studies have suggested a pivotal role for this cortical region in executive functions and in the regulation of cognition, emotion, and behavior. These appear to be two essential processes characterizing the neural networks involving prefrontal cortex. When attention, memory, goal-directed behaviors, emotions, and social interaction are no longer regulated by the knowledge systems and operational features of executive functions, the result is a wide range of overregulated, under-regulated, and erratically regulated processes producing symptoms that are diverse and disabling, yet at times surprisingly subtle and discounted by the untrained examiner. This is not to say that the prefrontal cortex is the sole mediator of such processes, as numerous studies have indicated that similar signs and symptoms can be associated with other sites of cerebral damage, including the basal ganglia, thalamus and certain nonfrontal cortical regions (Cummings, 1993; Eslinger and Grattan, 1993; Bogousslavsky, 1994; Mega and Cummings, 1994). Rather, the prefrontal cortex participates in multiple cortical-cortical and corticalsubcortical neural networks that have high integrative demands in cognitive and emotional domains.

The role of the prefrontal cortex in cognitive aspects of behavior has been widely recognized, including processes such as object and spatial working memory, planning, and strategic problem solving. Its role in emotional aspects of behavior, previously subsumed under the rubic of personality, has recently engendered renewed interest, as understanding of emotional processes has yielded better experimental tasks and measures for animal and human studies. With these developments, it has become clear that prefrontal cortex is a kind of melting pot for diverse influences on behavior and psychological processes, including cognitive, experiential, emotional and social-environmental. Optimally, the result can be a marvellous amplification of expertise and adaptation that permits individuals to accomplish goals they thought not possible, and to engage productively in many different facets of human experience throughout their life.