ABSTRACT
The frontal lobes have long been thought to play an important role in planning behaviour. For example, Harlow (1868), argued that frontal lobe lesions in humans result in a loss of “planning skill”, whilst much later Bianchi (1922) described a loss in the ability to “coordinate the different elements of a complex activity” in monkeys with large frontal lesions. More contemporary accounts have characterized the role of the frontal cortex in planning behaviour using similarly descriptive, terms; e.g., “as a general system for sequencing or guiding behaviour towards the attainment of an immediate or distant goal” (Jouandet and Gazzaniga, 1979), or as crucial for the “planning of future actions” (for review, see Shallice, 1988). Until recently, however, the assumed relationship between cognitive planning and the frontal lobes lacked solid empirical support and was based largely on anecdotal reports of disorganized behaviour in patients with relatively non-specific brain injury, or on the behaviour of monkeys with large excisions of the frontal cortex. Moreover, planning difficulties are not unique to patients with circumscribed frontal lobe damage. For example, “frontal-like” planning deficits have been described in patients with mild Parkinson’s disease (Morris, Downes, Evenden, Sahakian, Heald, & Robbins 1988; Owen et al., 1992; Owen, Sahakian, Hodges, Summers, Polkey, & Robbins, 1995a; Owen, Doyon, Dagher, & Evans, 1998), and other basal-ganglia disorders, suggesting that an equivalence between the prefrontal cortex and planning function cannot be assumed.
