Executive functions (collectively referred to as executive function and cognitive control) are a set of cognitive processes that are necessary for the cognitive control of behavior: selecting and successfully monitoring behaviors that facilitate the attainment of chosen goals. Executive functions include basic cognitive processes such as attentional control, cognitive inhibition, inhibitory control, working memory, and cognitive flexibility. Higher order executive functions require the simultaneous use of multiple basic executive functions and include planning and fluid intelligence (e.g., reasoning and problem solving).
Executive functions gradually develop and change across the lifespan of an individual and can be improved at any time over the course of a person’s life. Similarly, these cognitive processes can be adversely affected by a variety of events which affect an individual. Both neuropsychological tests (e.g., the Stroop test) and rating scales (e.g., the Behavior Rating Inventory of Executive Function) are used to measure executive functions. They are usually performed as part of a more comprehensive assessment to diagnose neurological and psychiatric disorders.
Cognitive control and stimulus control, which is associated with operant and classical conditioning, represent opposite processes (internal vs external or environmental, respectively) that compete over the control of an individual’s elicited behaviors; in particular, inhibitory control is necessary for overriding stimulus-driven behavioral responses (stimulus control of behavior). The prefrontal cortex is necessary but not solely sufficient for executive functions; for example, the caudate nucleus and subthalamic nucleus also have a role in mediating inhibitory control.
Cognitive control is impaired in addiction, attention deficit hyperactivity disorder, autism, and a number of other central nervous system disorders. Stimulus-driven behavioral responses that are associated with a particular rewarding stimulus tend to dominate one’s behavior in an addiction.
Neuroanatomy Of Executive Function
Historically, the executive functions have been seen as regulated by the prefrontal regions of the frontal lobes, but it is still a matter of ongoing debate if that really is the case. Even though articles on prefrontal lobe lesions commonly refer to disturbances of executive functions and vice versa, a review found indications for the sensitivity but not for the specificity of executive function measures to frontal lobe functioning. This means that both frontal and non-frontal brain regions are necessary for intact executive functions. Probably the frontal lobes need to participate in basically all of the executive functions, but it is not the only brain structure involved.
Neuroimaging and lesion studies have identified the functions which are most often associated with the particular regions of the prefrontal cortex and associated areas.
The dorsolateral prefrontal cortex (DLPFC) is involved with “on-line” processing of information such as integrating different dimensions of cognition and behavior. As such, this area has been found to be associated with verbal and design fluency, ability to maintain and shift set, planning, response inhibition, working memory, organisational skills, reasoning, problem solving and abstract thinking.
The anterior cingulate cortex (ACC) is involved in emotional drives, experience and integration. Associated cognitive functions include inhibition of inappropriate responses, decision making and motivated behaviors. Lesions in this area can lead to low drive states such as apathy, abulia or akinetic mutism and may also result in low drive states for such basic needs as food or drink and possibly decreased interest in social or vocational activities and sex.
The orbitofrontal cortex (OFC) plays a key role in impulse control, maintenance of set, monitoring ongoing behavior and socially appropriate behaviors. The orbitofrontal cortex also has roles in representing the value of rewards based on sensory stimuli and evaluating subjective emotional experiences. Lesions can cause disinhibition, impulsivity, aggressive outbursts, sexual promiscuity and antisocial behavior.
Furthermore, in their review, Alvarez and Emory state that:
“The frontal lobes have multiple connections to cortical, subcortical and brain stem sites. The basis of ‘higher-level’ cognitive functions such as inhibition, flexibility of thinking, problem solving, planning, impulse control, concept formation, abstract thinking, and creativity often arise from much simpler, ‘lower-level’ forms of cognition and behavior. Thus, the concept of executive function must be broad enough to include anatomical structures that represent a diverse and diffuse portion of the central nervous system.”
The executive functions are among the last mental functions to reach maturity. This is due to the delayed maturation of the prefrontal cortex, which is not completely myelinated until well into a person’s third decade of life.
Development of executive functions tends to occur in spurts, when new skills, strategies, and forms of awareness emerge. These spurts are thought to reflect maturational events in the frontal areas of the brain.
Attentional control appears to emerge in infancy and develop rapidly in early childhood. Cognitive flexibility, goal setting, and information processing usually develop rapidly during ages 7–9 and mature by age 12. Executive control typically emerges shortly after a transition period at the beginning of adolescence.
It is not yet clear whether there is a single sequence of stages in which executive functions appear, or whether different environments and early life experiences can lead people to develop them in different sequences.
Inhibitory control and working memory act as basic executive functions that makes it possible for more complex executive functions like problem-solving to develop. Inhibitory control and working memory are among the earliest executive functions to appear, with initial signs observed in infants, 7 to 12-months old. Then in the preschool years, children display a spurt in performance on tasks of inhibition and working memory, usually between the ages of 3 to 5 years.
Also during this time, cognitive flexibility, goal-directed behavior, and planning begin to develop. Nevertheless, preschool children do not have fully mature executive functions and continue to make errors related to these emerging abilities – often not due to the absence of the abilities, but rather because they lack the awareness to know when and how to use particular strategies in particular contexts.
Preadolescent children continue to exhibit certain growth spurts in executive functions, suggesting that this development does not necessarily occur in a linear manner, along with the preliminary maturing of particular functions as well. During preadolescence, children display major increases in verbal working memory; goal-directed behavior (with a potential spurt around 12 years of age); response inhibition and selective attention; and strategic planning and organizational skills.
Additionally, between the ages of 8 to 10, cognitive flexibility in particular begins to match adult levels. However, similar to patterns in childhood development, executive functioning in preadolescents is limited because they do not reliably apply these executive functions across multiple contexts as a result of ongoing development of inhibitory control.
Many executive functions may begin in childhood and preadolescence, such as inhibitory control. Yet, it is during adolescence when the different brain systems become better integrated. At this time, youth implement executive functions, such as inhibitory control, more efficiently and effectively and improve throughout this time period.
Just as inhibitory control emerges in childhood and improves over time, planning and goal-directed behavior also demonstrate an extended time course with ongoing growth over adolescence. Likewise, functions such as attentional control, with a potential spurt at age 15, along with working memory, continue developing at this stage.
The major change that occurs in the brain in adulthood is the constant myelination of neurons in the prefrontal cortex. At age 20–29, executive functioning skills are at their peak, which allows people of this age to participate in some of the most challenging mental tasks. These skills begin to decline in later adulthood.
Working memory and spatial span are areas where decline is most readily noted. Cognitive flexibility, however, has a late onset of impairment and does not usually start declining until around age 70 in normally functioning adults. Impaired executive functioning has been found to be the best predictor of functional decline in the elderly. Alvarez, Julie A.; Emory, Eugene (2006). Executive function and the frontal lobes: A meta-analytic review. Neuropsychology Review. 16 (1): 17–42.  Clark, L; Bechara, A; Damasio, H; Aitken, MRF; Sahakian, BJ; Robbins, TW (2008). Differential effects of insular and ventromedial prefrontal cortex lesions on risky decision making. Brain. 131 (5): 1311–1322.  Allman, John M.; Hakeem, Atiya; Erwin, Joseph M.; Nimchinsky, Esther; Hof, Patrick (2001). The anterior cingulate cortex: the evolution of an interface between emotion and cognition. Annals of the New York Academy of Sciences. 935 (1): 107–117.  Anderson, PJ (2002). Assessment and development of executive functioning (EF) in childhood. Child Neuropsychology. 8 (2): 71–82.  De Luca, CR; Wood, SJ; Anderson, V; Buchanan, JA; Proffitt, T; Mahony, K; Pantelis, C (2003). Normative data from the CANTAB I: Development of executive function over the lifespan. Journal of Clinical and Experimental Neuropsychology. 25 (2): 242–254.