Executive Functions Disorders

Introduction

Executive functions are those which regulate, control and direct human behaviour. Mental activity and human behaviour would not be possible without a system to control, organize and direct them. The executive system ensures that the different cognitive and emotional subsystems function in a coordinated way as they activate and deactivate the different functional circuits implicated in any human activity. The concept of executive function can be studied in Luria's (1966) Higher Cortical Function in Man, which was popularized in neuropsychology by Lezak (1976) and further developed by Fuster (1980) and Stuss and Benson (1986).

According to Lezak (1995: 42), executive functions are those abilities which allow an individual to function with independence, with a set goal, and with self-sufficient behaviour in a satisfactory manner. As long as the executive functions are intact, an individual may lose important cognitive abilities yet continue to be independent, constructively self-sufficient and productive. However, and no matter the state of the cognitive functions, should the executive functions become impaired, one is no longer able to care for oneself, to work for oneself or others, nor to maintain normal social relationships.

Executive functions are to be considered as different from the cognitive functions. The latter specifically refer to the reception and generation of information or to the stimulation received from any of the senses. Cognitive functions are attention, perception, language, memory, mental images, or higher motor functions. Executive functions are concerned with the organization of cognition and emotion and, when necessary, in their timing. Thus, cognitive impairment will especially affect the functional area involved, while executive impairment will affect the controlling functions and will therefore be reflected in a more general way in the individual's behaviour.

The anterior part of the brain is of extraordinary importance in the coordination and integration of the cognitive activity carried out in the posterior part of the brain. This is especially so with regard to the components of anticipation, initiating activity and even for decision-making. The frontal cortex is at the highest level within the hierarchy of the neural structures dedicated to the representation and performance of the activities of the organism. There are three prefrontal functions that ensure the integrity and purpose of all the novel and complex sequences of goal-directed behaviour. Two are chiefly based in the dorsolateral cortex (preparatory set and working memory) and the other in the orbital cortex (inhibitory control). The prefrontal cortex is the anatomical basis of these control functions, especially when active control is required during the process of learning a new activity. Once the activity becomes routine, the active control is [Page 392]carried out by another brain area and not necessarily by the prefrontal cortex (León-Carrión & Barroso y Martín, 1997; Shallice, 1982).

A revision of the specialized literature concerning problem solving, planning, prospective, control and performance associates these functions with the frontal lobe due to how these functions are affected when injury is incurred in this area of the brain, and especially in the prefrontal areas (León-Carrión, 1997; Lezak, 1995).

The classic tests that have most commonly been used to assess these functions are the Stroop Test (Stroop, 1935; Leon-Carrion, 1998), sorting tasks such as the Wisconsin Card Sorting Test (Grant & Berg, 1948), category tasks such as the Category Test (Halstead, 1947), problem solving tasks such as in the different versions of the Tower of Hanoi (Anzai & Simon, 1979; León-Carrión et al., 1991; and Leóon-Carrión, 1998) or maze tests such as the Porteus Maze Test (Porteus, 1959). A good set of clinical frontal tasks for frontal lobe deficits are those from Luria/Christensen's Neuropsychological Investigation (Christensen, 1975).

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