Executive functions are a rather loosely defined set of cognitive functions. The term derives from the CENTRAL EXECUTIVE, a process at the centre of the model of WORKING MEMORY presented and developed by Alan Baddeley and his colleagues. In a lucid discussion of executive functions, Roberts et al. (1998, p. 221) identify them as involving ‘the optimal scheduling of operation of different components of complex tasks that depend on more dedicated or modular mechanisms (generally mediated by posterior cortical structures). This collection of operations [incorporates] supervisory functions, including for example appropriate inhibitory mechanisms (for example, for selective attention and switching between two or more tasks) and also the monitoring of processes such as retrieval from long term memory and also of performance of intended actions.’ There is a degree of consensus in the literature that the term executive function covers processes such as these. There are three debates about it though: first, to what extent is executive function a monolithic construct? Are the separate components in fact independent, and if they are, to what extent can the term executive function be considered valuable? There is a dangerous trend in the literature to use the term rather indiscriminately, which restricts its value considerably. As with the term LIMBIC SYSTEM in NEUROANATOMY, indiscriminate and unspecified usage may debase the concept of executive function to a point where it has no useful meaning at all. Second, are executive functions localizable with the CENTRAL NERVOUS SYSTEM? In many cases executive function appears to be used as a term to describe the functions of the PREFRONTAL CORTEX, but this is a tendency that should be avoided. So, for example, the term DYSEXECUTIVE SYNDROME has been applied to a condition in which executive functions are impaired following brain damage of one sort or another. Patients with FRONTAL LOBE damage do show dysexecutive syndrome, but it is equally clear that not all patients with frontal damage show it and, moreover, patients with damage outside the frontal lobes can show dysexecutive syndrome. A unique association between the prefrontal cortex and executive functions appears very unlikely.
The third point of discussion concerns two things: the dissociation of executive and non-executive functions and the relationships between executive functions and constructs such as will (see WILLED ACTION) and CONSCIOUSNESS. Both psychologists and philosophers have become embroiled in a debate about the nature of these functions. Rabbitt (1997) identifies the fact that executive functions have much to do with ‘novel tasks that require us to formulate a goal, to plan, and to choose between alternative sequences of behaviour to reach this goal, to compare these plans in respect of their relative probabilities of success and their relative efficiency in attaining the chosen goal, to initiate the plan selected and to carry it through, amending it as necessary, until it is successful or until impending failure is recognized’ (p3).
But Rabbitt notes that complex sequences of actions can be carried out automatically, without obvious ‘conscious’ control. What distinguishes executive function from non-executive is the degree to which behaviour is controlled automatically. This executive functions appear to relate to conditions in which strategic planning; the initiation of novel behavioural sequences; the active suppression of inappropriate behaviour; allocation of processing resources to more than one task; ‘on line’ monitoring of performance; and SUSTAINED ATTENTION are all required. Rabbitt distinguishes such processes from automatic functions. These are driven by environmental contingencies and can be thought of as being much the same as HABITS or motor programmes (see MOTOR PROGRAMMING). It is thus conceivable that what starts as an executive function could through repetition become an automatic sequence. The important point to note though is that it is not task complexity per se that discriminates executive function from non-executive, but such things as novelty and strategic planning. Whether this implies that executive function must be conscious is not clear: some authors imply that there must be a degree of conscious control involved in executive function while others do not. This is a particularly interesting point when considering whether animals other than humans use executive functions. It can be argued, for example, that a laboratory rat, negotiating a complex task such as a RADIAL ARM MAZE for the first time, is in a novel situation and must develop plans and strategies appropriate to its test environment. In humans such processes would be classified as executive, and it is difficult to see why they should not be classified in the same way in a rodent: but are rats and humans conscious in the same way?
