ABSTRACT
Executive functions are the neurocognitive operations that enable purposeful behavior as it unfolds in time. By this we mean behavior above the level of reflex or instinct, organized by purposes (goals) at multiple levels of complexity and abstractness. This definition embodies three central themes that we wish to highlight. The first is the idea of goals, or endstates, guiding or directing behavior. This theme is of course a familiar one in conceptualizations of executive function. The importance of cortical regulatory mechanisms that use in some way representations of goals to plan, initiate, maintain, and adjust behavior was emphasized by Bianchi (cited in Benton, 1991) and Luria (1966), among others. These investigators based their ideas largely on both subtle and dramatic breakdowns in the structure of goal-directed activity observed in monkeys and humans, respectively, with brain lesions primarily affecting prefrontal cortex. Such observations were influential because the loss of goal-directedness, or purpose, to behavior appeared to occur in the absence of more basic or primary deficits in sensory or motor function. Thus there must be separate-probably frontal-cortical systems specialized for this type of behavioral control.
