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Executive functions
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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.[1] Executive functions include basic cognitive processes such as attentional control, cognitive inhibition, inhibitory control, working memory, and cognitive flexibility.[2][3] Higher order executive functions require the simultaneous use of multiple basic executive functions and include planning and fluid intelligence (i.e., reasoning and problem solving).[2][3]

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.[2] Similarly, these cognitive processes can be adversely affected by a variety of events which affect an individual.[2] 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 (i.e., internal vs external or environmental, respectively) that compete over the control of an individual's elicited behaviors;[4] in particular, inhibitory control is necessary for overriding stimulus-driven behavioral responses (i.e., stimulus control of behavior).[2] The prefrontal cortex is necessary but not solely sufficient for executive functions;[2][5][6] for example, the caudate nucleus and subthalamic nucleus also have a role in mediating inhibitory control.[2][7]

Cognitive control is impaired in addiction,[7] attention deficit hyperactivity disorder,[2][7] 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.[7]

Contents

1 Neuroanatomy
2 Hypothesized role
3 Historical perspective
4 Development
4.1 Early childhood
4.2 Preadolescence
4.3 Adolescence
4.4 Adulthood
5 Models
5.1 Top-down inhibitory control
5.2 Working memory model
5.3 Supervisory attentional system (SAS)
5.4 Self-regulatory model
5.5 Problem-solving model
5.6 Lezak's conceptual model
5.7 Miller & Cohen's model
5.8 Miyake and Friedman's model
5.9 Banich's "Cascade of control" model
6 Assessment
7 Experimental evidence
7.1 Context-sensitivity of PFC neurons
7.2 Attentional biasing in sensory regions
7.3 Connectivity between the PFC and sensory regions
7.4 Bilingualism and executive functions
8 In disease
9 Future directions
10 See also
11 References
12 External links

Neuroanatomy

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.[5] 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.[5]

Neuroimaging and lesion studies have identified the functions which are most often associated with the particular regions of the prefrontal cortex.[5]

The dorsolateral prefrontal cortex (DLPFC) is involved with "on-line" processing of information such as integrating different dimensions of cognition and behaviour.[8] 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.[5][9]

Side view of the brain, illustrating dorsolateral prefrontal and orbitofrontal cortex

The anterior cingulate cortex (ACC) is involved in emotional drives, experience and integration.[8] Associated cognitive functions include inhibition of inappropriate responses, decision making and motivated behaviours. 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.[8][10]
The orbitofrontal cortex (OFC) plays a key role in impulse control, maintenance of set, monitoring ongoing behaviour and socially appropriate behaviours.[8] The orbitofrontal cortex also has roles in representing the value of rewards based on sensory stimuli and evaluating subjective emotional experiences.[11] Lesions can cause disinhibition, impulsivity, aggressive outbursts, sexual promiscuity and antisocial behaviour.[5]

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."[5]

The cerebellum also appears to be involved in mediating certain executive functions.[12][13]
Hypothesized role

The executive system is thought to be heavily involved in handling novel situations outside the domain of some of our 'automatic' psychological processes that could be explained by the reproduction of learned schemas or set behaviors. Psychologists Don Norman and Tim Shallice have outlined five types of situations in which routine activation of behavior would not be sufficient for optimal performance:[14][page needed]

Those that involve planning or decision making
Those that involve error correction or troubleshooting
Situations where responses are not well-rehearsed or contain novel sequences of actions
Dangerous or technically difficult situations
Situations that require the overcoming of a strong habitual response or resisting temptation.

A prepotent response is a response for which immediate reinforcement (positive or negative) is available or has been previously associated with that response.[15][page needed] The executive functions are often invoked when it is necessary to override these prepotent responses that might otherwise be automatically elicited by stimuli in the external environment. For example, on being presented with a potentially rewarding stimulus, such as a tasty piece of chocolate cake, a person might have the automatic response to take a bite. However, where such behavior conflicts with internal plans (such as having decided not to eat chocolate cake while on a diet), the executive functions might be engaged to inhibit that response.

Although suppression of these prepotent responses is ordinarily considered adaptive, problems for the development of the individual and the culture arise when feelings of right and wrong are overridden by cultural expectations or when creative impulses are overridden by executive inhibitions.[16][page needed]
Historical perspective

Although research into the executive functions and their neural basis has increased markedly over recent years, the theoretical framework in which it is situated is not new. In the 1940s, the British psychologist Donald Broadbent drew a distinction between "automatic" and "controlled" processes (a distinction characterized more fully by Shiffrin and Schneider in 1977),[17] and introduced the notion of selective attention, to which executive functions are closely allied. In 1975, the US psychologist Michael Posner used the term "cognitive control" in his book chapter entitled "Attention and cognitive control".[18]

The work of influential researchers such as Michael Posner, Joaquin Fuster, Tim Shallice, and their colleagues in the 1980s (and later Trevor Robbins, Bob Knight, Don Stuss, and others) laid much of the groundwork for recent research into executive functions. For example, Posner proposed that there is a separate "executive" branch of the attentional system, which is responsible for focusing attention on selected aspects of the environment.[19] The British neuropsychologist Tim Shallice similarly suggested that attention is regulated by a "supervisory system", which can override automatic responses in favour of scheduling behaviour on the basis of plans or intentions.[20] Throughout this period, a consensus emerged that this control system is housed in the most anterior portion of the brain, the prefrontal cortex (PFC).

Psychologist Alan Baddeley had proposed a similar system as part of his model of working memory[21] and argued that there must be a component (which he named the "central executive") that allows information to be manipulated in short-term memory (for example, when doing mental arithmetic).
Development
Further information: Neurobiological effects of physical exercise § Cognitive control and memory

When studying executive functions, a developmental framework is helpful because these abilities mature at different rates over time. Some abilities peak maturation rate in late childhood or adolescence while others' progress into early adulthood. The brain continues to mature and develop connections well into adulthood. A person's executive function abilities are shaped by both physical changes in the brain and by life experiences, in the classroom and in the world at large. Furthermore, executive functioning development corresponds to the neurophysiological developments of the growing brain; as the processing capacity of the frontal lobes and other interconnected regions increases, the core executive functions emerge.[22][23] As these functions are established, they continue to mature, sometimes in spurts, while other, more complex functions also develop, underscoring the different directions along which each component might develop.[22][23]
Early childhood

Inhibitory control and working memory act as basic executive functions that makes it possible for more complex executive functions like problem-solving to develop.[24] Inhibitory control and working memory are among the earliest executive functions to appear, with initial signs observed in infants, 7 to 12-months old.[22][23] 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.[22][25] Also during this time, cognitive flexibility, goal-directed behavior, and planning begin to develop.[22] 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.[26]
Preadolescence

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.[22][23] During preadolescence, children display major increases in verbal working memory;[27] goal-directed behavior (with a potential spurt around 12 years of age);[28] response inhibition and selective attention;[29] and strategic planning and organizational skills.[23][30][31] Additionally, between the ages of 8 to 10, cognitive flexibility in particular begins to match adult levels.[30][31] 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.[22]
Adolescence

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.[32][33] 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.[25][28] Likewise, functions such as attentional control, with a potential spurt at age 15,[28] along with working memory,[32] continue developing at this stage.
Adulthood

The major change that occurs in the brain in adulthood is the constant myelination of neurons in the prefrontal cortex.[22] 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.[22] Impaired executive functioning has been found to be the best predictor of functional decline in the elderly.
Models
Top-down inhibitory control

Aside from facilitatory or amplificatory mechanisms of control, many authors have argued for inhibitory mechanisms in the domain of response control,[34] memory,[35] selective attention,[36] theory of mind,[37][38] emotion regulation,[39] as well as social emotions such as empathy.[40] A recent review on this topic argues that active inhibition is a valid concept in some domains of psychology/cognitive control.[41]
Working memory model

One influential model is Baddeley's multicomponent model of working memory, which is composed of a central executive system that regulates three other subsystems: the phonological loop, which maintains verbal information; the visuospatial sketchpad, which maintains visual and spatial information; and the more recently developed episodic buffer that integrates short-term and long-term memory, holding and manipulating a limited amount of information from multiple domains in temporal and spatially sequenced episodes.[21][42]
Supervisory attentional system (SAS)

Another conceptual model is the supervisory attentional system (SAS).[43][44] In this model, contention scheduling is the process where an individual's well-established schemas automatically respond to routine situations while executive functions are used when faced with novel situations. In these new situations, attentional control will be a crucial element to help generate new schema, implement these schema, and then assess their accuracy.
Self-regulatory model

Russell Barkley proposed a widely known model of executive functioning that is based on self-regulation[disambiguation needed]. Primarily derived from work examining behavioral inhibition, it views executive functions as composed of four main abilities.[45] One element is working memory that allows individuals to resist interfering information. A second component is the management of emotional responses in order to achieve goal-directed behaviors. Thirdly, internalization of self-directed speech is used to control and sustain rule-governed behavior and to generate plans for problem-solving. Lastly, information is analyzed and synthesized into new behavioral responses to meet one's goals. Changing one's behavioral response to meet a new goal or modify an objective is a higher level skill that requires a fusion of executive functions including self-regulation, and accessing prior knowledge and experiences.

According to this model, the executive system of the human brain provides for the cross-temporal organization of behavior towards goals and the future and coordinates actions and strategies for everyday goal-directed tasks. Essentially, this system permits humans to self-regulate their behavior so as to sustain action and problem solving toward goals specifically and the future more generally. Thus, executive function deficits pose serious problems for a person's ability to engage in self-regulation over time to attain their goals and anticipate and prepare for the future.[46]
Problem-solving model

Yet another model of executive functions is a problem-solving framework where executive functions is considered a macroconstruct composed of subfunctions working in different phases to (a) represent a problem, (b) plan for a solution by selecting and ordering strategies, (c) maintain the strategies in short-term memory in order to perform them by certain rules, and then (d) evaluate the results with error detection and error correction.[47]


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