2010 Volume 12 Issue 3+4 Pages 156-164
Executive function is defined as a brain function dedicated to sustain a proper mental set for the purpose of accomplishing a future goal, and comprises of four steps of 1) the goal formation, 2) planning, 3) goal-directed actions and 4) effective performance [Lezak MD 1982]. More specifically, one has first to set a future goal with definite intention, secondly to consider and select most appropriate strategies that should be taken, thirdly to initiate and sustain constantly goal-directed actions while adding appropriate amendments to the plans and methods, and finally to organize the most efficient strategies by reviewing the past progresses as well as estimating the extent of future courses still left before reaching the goal.
Among various cognitive functions, executive function may be regarded as a higher-order function that controls efficiency and purpose-directed operations of other subordinate cognitive functions such as memory, language and visuospatial skills.
Executive function may be assessed globally by short bedside tests represented by the Frontal Assessment Battery [Dubois B et al. 2000] and more complex and detailed test batteries such as the Behavioural Assessment of the Dysexecutive Syndrome [Wilson BA et al. 1996]. Further, “executive function”, when taken as a general umbrella term, may comprise of several associated brain functions, each of which represents specific aspect of “executive function”. Among these functions are 1) divided attention and a capacity to manage multiple and simultaneous tasks that may be tested by the “Kana Hiroi” (phonemic letter picking-up) Test and the Trail Making Test, 2) capability for mentalset shifting assessed by the Stroop Test, 3) psychomotor speed tapped by the semantic or phonemic word fluency test, and 4) abilities in recursive speculations that may be tested by the Wisconsin Card Sorting Test or Tower of Hanoi.
Dysexecutive syndrome may be elicited by damage to the dorsolateral prefrontal cortex and/or its projection to the striatum, namely the dorsolateral prefrontal circuit, one of five functional neural circuits between the frontal lobes and the striata. Cognitively associated fronto-striate circuits also include the lateral orbitofrontal circuit that is involved in inhibitory control of behaviors, and anterior cingulate circuit that is involved in maintenance of initiatives and interests in the outside milieu. Damage to the former may induce disinhibition and antisocial behaviors, and damage to the latter may cause inertia and apathy. Dysexecutive syndrome may be accompanied by other frontal symptoms such as behavioral and emotional impairment and these additional impairments may alternatively hamper executive function further.
