Executive functions
In cognitive science and neuropsychology, executive functions are a set of cognitive processes that support goal-directed behavior, by regulating thoughts and actions through cognitive control, selecting and successfully monitoring actions that facilitate the attainment of chosen objectives. 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.
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 and rating scales 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 that compete over the control of an individual's elicited behaviors; in particular, inhibitory control is necessary for overriding stimulus-driven behavioral responses. 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
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 they are 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 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, anticipation of conflict stimuli, working memory, organisational skills, reasoning, problem-solving, and abstract thinking.
- The anterior cingulate cortex 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 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.
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 cerebellum also appears to be involved in mediating certain executive functions, as do the ventral tegmental area and the substantia nigra.
In humans, high contents of cannabinoid receptor 1 is found in frontal neocortical areas, subserving higher cognitive and executive functions, and in the posterior cingulate, a region pivotal for consciousness and higher cognitive processing by its activation.
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:- 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.
Executive functions are often invoked when it is necessary to override 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, 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.
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, 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".The work of influential researchers such as Michael Posner, Joaquin Fuster, Tim Shallice, and their colleagues in the 1980s 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. 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. Throughout this period, a consensus emerged that this control system is housed in the most anterior portion of the brain, the prefrontal cortex.
Psychologist Alan Baddeley had proposed a similar system as part of his model of working memory and argued that there must be a component that allows information to be manipulated in short-term memory.