Executive functions
Encyclopedia
The executive system is a theorized cognitive system in psychology
that controls and manages other cognitive processes. It is responsible for processes that are sometimes referred to as the executive function, executive functions, supervisory attentional system, or cognitive control. These functions are largely carried out by prefrontal areas
of the frontal lobe
.
Executive function is an umbrella term for cognitive processes
such as planning, working memory
, attention
, problem solving, verbal reasoning, inhibition, mental flexibility, multi-tasking, initiation and monitoring of actions.
of the frontal lobe
. These areas have multiple connections with other cortical
, subcortical and brainstem regions. Neuroimaging
and lesion
studies have identified the functions which are most often associated with the particular regions of the prefrontal cortex.
The dorsolateral prefrontal cortex
is involved with “on-line” processing of information such as integrating different dimensions of cognition and behaviour. As such, this area has been found to be associated with verbal and design fluency, ability of maintain and shift set, planning, response inhibition, 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 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.
The orbitofrontal cortex
plays a key role in impulse control, maintenance of set, monitoring ongoing behaviour and socially appropriate behaviours. 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 behaviour.
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:
The executive functions are often invoked when it is necessary to override 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.
The neural mechanisms by which the executive functions are implemented is a topic of ongoing debate in the field of cognitive neuroscience
. Traditionally, there has been a strong focus on the frontal lobes, but more recent brain research indicates that executive functions are far more distributed across the cortex.
drew a distinction between "automatic" and "controlled" processes (a distinction characterized more fully by Shiffrin
and Schneider in 1977), 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 (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. 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
(PFC).
Psychologist Alan Baddeley
had proposed a similar system as part of his model of working memory
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).
. 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.
, emotion regulation, as well as social emotions such as empathy. A recent review on this topic argues that active inhibition is a valid concept in some domains of psychology/cognitive control.
of sensory or motor neuron
s that are engaged by task- or goal-relevant elements of the external environment. In a key paragraph, they argue:
Miller and Cohen draw explicitly upon an earlier theory of visual attention that conceptualises perception of visual scenes in terms of competition among multiple representations - such as colors, individuals, or objects. Selective visual attention acts to 'bias' this competition in favour of certain selected features or representations. For example, imagine that you are waiting at a busy train station for a friend who is wearing a red coat. You are able to selectively narrow the focus of your attention to search for red objects, in the hope of identifying your friend. Desimone and Duncan argue that the brain achieves this by selectively increasing the gain of neurons responsive to the color red, such that output from these neurons is more likely to reach a downstream processing stage
, and, as a consequence, to guide behaviour. According to Miller and Cohen, this selective attention mechanism is in fact just a special case of cognitive control - one in which the biasing occurs in the sensory domain. According to Miller and Cohen's model, the PFC can exert control over input (sensory) or output (response) neuron
s, as well as over assemblies involved in memory
, or emotion
. Cognitive control is mediated by reciprocal PFC connectivity
with the sensory
and motor cortices
, and with the limbic system
. Within their approach, thus, the term 'cognitive control' is applied to any situation where a biasing signal is used to promote task-appropriate responding, and control thus becomes a crucial component of a wide range of psychological constructs such as selective attention, error monitoring, decision-making, memory inhibition
, and response inhibition.
Miyake and Friedman also suggest that the current body of research in executive functions suggest four general conclusions about these skills. The first conclusion is the unity and diversity aspects of executive functions. Second, recent studies suggest that much of one’s EF skills are inherited genetically, as demonstrated in twin studies. Third, clean measures of executive functions can differentiate between normal and clinical or regulatory behaviors, such as ADHD. Last, longitudinal studies demonstrate that EF skills are relatively stable throughout development.
This is largely due to the nature of the executive system itself. It is mainly concerned with the dynamic, "online" co-ordination of cognitive resources, and, hence, its effect can be observed only by measuring other cognitive processes. In similar manner, it does not always fully engage outside of real-world situations. As neurologist
Antonio Damasio
has reported, a patient with severe day-to-day executive problems may still pass paper-and-pencil or lab-based tests of executive function.
Theories of the executive system were largely driven by observations of patients having suffered frontal lobe
damage. They exhibited disorganized actions and strategies for everyday tasks (a group of behaviors now known as dysexecutive syndrome
) although they seemed to perform normally when clinical or lab-based tests were used to assess more fundamental cognitive functions such as memory
, learning
, language
, and reasoning. It was hypothesized that, to explain this unusual behaviour, there must be an overarching system that co-ordinates other cognitive resources.
Much of the experimental evidence for the neural structures involved in executive functions comes from laboratory tasks such as the Stroop task
or the Wisconsin Card Sorting Task (WCST). In the Stroop task, for example, human subjects are asked to name the color that color words are printed in when the ink color and word meaning often conflict (for example, the word "RED" in green ink). Executive functions are needed to perform this task, as the relatively overlearned and automatic behaviour (word reading) has to be inhibited in favour of a less practiced task - naming the ink color. Recent functional neuroimaging
studies have shown that two parts of the PFC, the anterior cingulate cortex
(ACC) and the dorsolateral prefrontal cortex
(DLPFC), are thought to be particularly important for performing this task.
studies in non-human primate
s, such as the macaque
monkey, which have shown that (in contrast to cells in the posterior brain) many PFC neurons are sensitive to a conjunction of a stimulus and a context. For example, PFC cells might respond to a green cue in a condition where that cue signals that a leftwards fast movement of an eye, head should be made, but not to a green cue in another experimental context. This is important, because the optimal deployment of executive functions is invariably context-dependent. To quote an example offered by Miller and Cohen, a US resident might have an overlearned response to look left when crossing the road. However, when the "context" indicates that he or she is in the UK
, this response would have to be suppressed in favour of a different stimulus-response pairing (look right when crossing the road). This behavioural repertoire clearly requires a neural system that is able to integrate the stimulus (the road) with a context (US, UK) to cue a behaviour (look left, look right). Current evidence suggests that neurons in the PFC appear to represent precisely this sort of information. Other evidence from single-cell electrophysiology
in monkeys implicates ventrolateral PFC (inferior prefrontal convexity) in the control of motor responses. For example, cells that increase their firing rate to NoGo signals as well as a signal that says "don't look there!" have been identified.
and functional neuroimaging
studies involving human
subjects have been used to describe the neural mechanisms underlying attentional biasing. Most studies have looked for activation at the 'sites' of biasing, such as in the visual
or auditory cortices. Early studies employed event-related potential
s to reveal that electrical brain responses recorded over left and right visual cortex are enhanced when the subject is instructed to attend to the appropriate (contralateral) side of space.
The advent of bloodflow-based neuroimaging techniques such as functional magnetic resonance imaging
(fMRI) and positron emission tomography
(PET) has more recently permitted the demonstration that neural activity in a number of sensory regions, including color-, motion-, and face-responsive
regions of visual cortex, is enhanced when subjects are directed to attend to that dimension of a stimulus, suggestive of gain control
in sensory neocortex. For example, in a typical study, Liu and coworkers presented subjects with arrays of dots moving to the left or right, presented in either red or green. Preceding each stimulus, an instruction cue indicated whether subjects should respond on the basis of the colour or the direction of the dots. Even though colour and motion were present in all stimulus arrays, fMRI activity in colour-sensitive regions (V4) was enhanced when subjects were instructed to attend to the colour, and activity in motion-sensitive regions was increased when subjects were cued to attend to the direction of motion. Several studies have also reported evidence for the biasing signal prior to stimulus onset, with the observation that regions of the frontal cortex tend to come active prior to the onset of an expected stimulus.
Bilingual individuals also seem to have an advantage in an area known as conflict processing, which occurs when there are multiple representations of one particular response (for example, a word in one language and its translation in the individual’s other language) . The lateral prefrontal cortex has been shown to be involved with conflict processing specifically.
, whereby posterior medial frontal cortex signals the need for increased executive functions and sends this signal on to areas in dorsolateral prefrontal cortex that actually implement control. Yet there has been no compelling evidence at all that this view is correct, and, indeed, one article showed that patients with lateral PFC damage had reduced ERNs (a putative sign of dorsomedial monitoring/error-feedback) - suggesting, if anything, that the direction of flow of the control could be in the reverse direction. Another prominent theory emphasises that interactions along the perpendicular axis of the frontal cortex, arguing that a 'cascade' of interactions between anterior PFC, dorsolateral PFC, and premotor cortex
guides behaviour in accordance with past context, present context, and current sensorimotor associations, respectively.
Advances in neuroimaging
techniques have allowed studies of genetic links to executive functions, with the goal of using the imaging techniques as potential endophenotype
s for discovering the genetic causes of executive function.
Psychology
Psychology is the study of the mind and behavior. Its immediate goal is to understand individuals and groups by both establishing general principles and researching specific cases. For many, the ultimate goal of psychology is to benefit society...
that controls and manages other cognitive processes. It is responsible for processes that are sometimes referred to as the executive function, executive functions, supervisory attentional system, or cognitive control. These functions are largely carried out by prefrontal areas
Prefrontal cortex
The prefrontal cortex is the anterior part of the frontal lobes of the brain, lying in front of the motor and premotor areas.This brain region has been implicated in planning complex cognitive behaviors, personality expression, decision making and moderating correct social behavior...
of the frontal lobe
Frontal lobe
The frontal lobe is an area in the brain of humans and other mammals, located at the front of each cerebral hemisphere and positioned anterior to the parietal lobe and superior and anterior to the temporal lobes...
.
Executive function is an umbrella term for cognitive processes
Cognition
In science, cognition refers to mental processes. These processes include attention, remembering, producing and understanding language, solving problems, and making decisions. Cognition is studied in various disciplines such as psychology, philosophy, linguistics, and computer science...
such as planning, working memory
Working memory
Working memory has been defined as the system which actively holds information in the mind to do verbal and nonverbal tasks such as reasoning and comprehension, and to make it available for further information processing...
, attention
Attention
Attention is the cognitive process of paying attention to one aspect of the environment while ignoring others. Attention is one of the most intensely studied topics within psychology and cognitive neuroscience....
, problem solving, verbal reasoning, inhibition, mental flexibility, multi-tasking, initiation and monitoring of actions.
Neuroanatomy
The executive functions are located primarily in the prefrontal regionsPrefrontal cortex
The prefrontal cortex is the anterior part of the frontal lobes of the brain, lying in front of the motor and premotor areas.This brain region has been implicated in planning complex cognitive behaviors, personality expression, decision making and moderating correct social behavior...
of the frontal lobe
Frontal lobe
The frontal lobe is an area in the brain of humans and other mammals, located at the front of each cerebral hemisphere and positioned anterior to the parietal lobe and superior and anterior to the temporal lobes...
. These areas have multiple connections with other cortical
Cerebral cortex
The cerebral cortex is a sheet of neural tissue that is outermost to the cerebrum of the mammalian brain. It plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. It is constituted of up to six horizontal layers, each of which has a different...
, subcortical and brainstem regions. Neuroimaging
Neuroimaging
Neuroimaging includes the use of various techniques to either directly or indirectly image the structure, function/pharmacology of the brain...
and lesion
Brain damage
"Brain damage" or "brain injury" is the destruction or degeneration of brain cells. Brain injuries occur due to a wide range of internal and external factors...
studies have identified the functions which are most often associated with the particular regions of the prefrontal cortex.
The dorsolateral prefrontal cortex
Dorsolateral prefrontal cortex
The dorsolateral prefrontal cortex , according to a more restricted definition, is roughly equivalent to Brodmann areas 9 and 46. According to a broader definition DL-PFC consists of the lateral portions of Brodmann areas 9 – 12, of areas 45, 46, and the superior part of area 47. These regions...
is involved with “on-line” processing of information such as integrating different dimensions of cognition and behaviour. As such, this area has been found to be associated with verbal and design fluency, ability of maintain and shift set, planning, response inhibition, working memory, organisational skills, reasoning, problem solving and abstract thinking.
The anterior cingulate cortex
Anterior cingulate cortex
The anterior cingulate cortex is the frontal part of the cingulate cortex, that resembles a "collar" form around the corpus callosum, the fibrous bundle that relays neural signals between the right and left cerebral hemispheres of the brain...
is involved in emotional drives, experience and integration. 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
Apathy
Apathy is a state of indifference, or the suppression of emotions such as concern, excitement, motivation and passion. An apathetic individual has an absence of interest in or concern about emotional, social, spiritual, philosophical or physical life.They may lack a sense of purpose or meaning in...
, abulia or akinetic mutism
Akinetic mutism
Akinetic mutism is a medical term describing patients who tend neither to speak nor move . It is the result of severe frontal lobe injury in which the pattern of inhibitory control is one of increasing passivity and gradually decreasing speech and motion.An example of a cause of this disorder...
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
Orbitofrontal cortex
The orbitofrontal cortex is a prefrontal cortex region in the frontal lobes in the brain which is involved in the cognitive processing of decision-making...
plays a key role in impulse control, maintenance of set, monitoring ongoing behaviour and socially appropriate behaviours. 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 behaviour.
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 schemasSchema (psychology)
A schema , in psychology and cognitive science, describes any of several concepts including:* An organized pattern of thought or behavior.* A structured cluster of pre-conceived ideas....
or set behaviors. Psychologists Don Norman and Tim Shallice
Tim Shallice
Timothy Shallice is a professor of neuropsychology and past director of the Institute of Cognitive Neuroscience, part of University College London...
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.
The executive functions are often invoked when it is necessary to override responses that might otherwise be automatically elicited by stimuli in the external environment. For example, on being presented with a potentially rewarding
Reinforcement
Reinforcement is a term in operant conditioning and behavior analysis for the process of increasing the rate or probability of a behavior in the form of a "response" by the delivery or emergence of a stimulus Reinforcement is a term in operant conditioning and behavior analysis for the process of...
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.
The neural mechanisms by which the executive functions are implemented is a topic of ongoing debate in the field of cognitive neuroscience
Cognitive neuroscience
Cognitive neuroscience is an academic field concerned with the scientific study of biological substrates underlying cognition, with a specific focus on the neural substrates of mental processes. It addresses the questions of how psychological/cognitive functions are produced by the brain...
. Traditionally, there has been a strong focus on the frontal lobes, but more recent brain research indicates that executive functions are far more distributed across the cortex.
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 1950s, the British psychologist Donald BroadbentDonald Broadbent
Donald Eric Broadbent FRS was an influential English experimental psychologist. His career and his research work bridged the gap between the pre-Second World War approach of Sir Frederic Bartlett and its wartime development into applied psychology, and what from the late 1960s became known as...
drew a distinction between "automatic" and "controlled" processes (a distinction characterized more fully by Shiffrin
Richard Shiffrin
Richard Shiffrin is the Luther Dana Waterman Professor of cognitive science for the Department of Psychological and Brain Sciences at Indiana University, Bloomington. Shiffrin has contributed a number of theories of attention and memory to the field of psychology. He co-authored the...
and Schneider in 1977), and introduced the notion of selective attention, to which executive functions are closely allied. In 1975, the US psychologist Michael Posner
Michael Posner (psychologist)
Michael I. Posner is the editor of numerous cognitive and neuroscience compilations and is an eminent researcher in the field of attention...
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
Joaquin Fuster
Joaquin M. Fuster is a neuroscientist whose research has made fundamental contributions to the understanding of the neural structures underlying cognition and behavior. His several books and hundreds of papers, particularly on memory and the prefrontal cortex, are widely cited.Born in Barcelona,...
, Tim Shallice
Tim Shallice
Timothy Shallice is a professor of neuropsychology and past director of the Institute of Cognitive Neuroscience, part of University College London...
, and their colleagues in the 1980s (and later Trevor Robbins
Trevor Robbins
Professor Trevor Robbins FRS FMedSci is Head of the Department of Experimental Psychology at the University of Cambridge, and a fellow of Downing College, Cambridge....
, 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
Attention
Attention is the cognitive process of paying attention to one aspect of the environment while ignoring others. Attention is one of the most intensely studied topics within psychology and cognitive neuroscience....
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
Prefrontal cortex
The prefrontal cortex is the anterior part of the frontal lobes of the brain, lying in front of the motor and premotor areas.This brain region has been implicated in planning complex cognitive behaviors, personality expression, decision making and moderating correct social behavior...
(PFC).
Psychologist Alan Baddeley
Alan Baddeley
Alan David Baddeley FRS, CBE is a British psychologist. He is professor of psychology at the University of York. He is known for his work on working memory, in particular for his multiple components model.-Education:...
had proposed a similar system as part of his model of working memory
Working memory
Working memory has been defined as the system which actively holds information in the mind to do verbal and nonverbal tasks such as reasoning and comprehension, and to make it available for further information processing...
and argued that there must be a component (which he named the "central executive") that allows information to be manipulated in short-term memory
Short-term memory
Short-term memory is the capacity for holding a small amount of information in mind in an active, readily available state for a short period of time. The duration of short-term memory is believed to be in the order of seconds. A commonly cited capacity is 7 ± 2 elements...
(for example, when doing mental arithmetic).
Development of Executive Functions
When studying executive functions, a developmental framework is helpful because these abilities mature at different rates over time, with some peaking in late childhood or adolescence while others progressing until early adulthood. 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. 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.Development in childhood
Previous research shows how inhibitory control and working memory act as basic executive functions that set the stage 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.Development in 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. 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.Development in 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, so youth implement executive functions, such as inhibitory control, more efficiently and effectively, improving 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.Development in adulthood
The major change that occurs in the brain in adulthood is the constant myelination of neurons in the prefrontal cortexPrefrontal cortex
The prefrontal cortex is the anterior part of the frontal lobes of the brain, lying in front of the motor and premotor areas.This brain region has been implicated in planning complex cognitive behaviors, personality expression, decision making and moderating correct social behavior...
. 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.
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, memory, selective attention, theory of mindTheory of mind
Theory of mind is the ability to attribute mental states—beliefs, intents, desires, pretending, knowledge, etc.—to oneself and others and to understand that others have beliefs, desires and intentions that are different from one's own...
, emotion regulation, as well as social emotions such as empathy. A recent review on this topic argues that active inhibition is a valid concept in some domains of psychology/cognitive control.
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.Supervisory Attentional System (SAS)
Another conceptual model is the supervisory attentional system (SAS). 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
Primarily derived from work examining behavioral inhibition, Barkley’s self-regulatory model views executive functions as composed of four main abilities. 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.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.Lezak’s Conceptual Model
One of the most widespread conceptual models on executive functions is Lezak’s model. This framework proposes four broad domains of volition, planning, purposive action, and effective performance as working together to accomplish global executive functioning needs. While this model may broadly appeal to clinicians and researchers to help identify and assess certain executive functioning components, it lacks a distinct theoretical basis and relatively few attempts at validation.Miller & Cohen's (2001) model
In 2001, Earl Miller and Jonathan Cohen published an influential article entitled 'An integrative theory of prefrontal cortex function' in which they argue that cognitive control is the primary function of the prefrontal cortex (PFC), and that control is implemented by increasing the gainGain
In electronics, gain is a measure of the ability of a circuit to increase the power or amplitude of a signal from the input to the output. It is usually defined as the mean ratio of the signal output of a system to the signal input of the same system. It may also be defined on a logarithmic scale,...
of sensory or motor neuron
Neuron
A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...
s that are engaged by task- or goal-relevant elements of the external environment. In a key paragraph, they argue:
'We assume that the PFC serves a specific function in cognitive control: the active maintenance of patterns of activity that represent goals and the means to achieve them. They provide bias signals throughout much of the rest of the brain, affecting not only visual processes but also other sensory modalities, as well as systems responsible for response execution, memory retrieval, emotional evaluation, etc. The aggregate effect of these bias signals is to guide the flow of neural activity along pathways that establish the proper mappings between inputs, internal states, and outputs needed to perform a given task.'
Miller and Cohen draw explicitly upon an earlier theory of visual attention that conceptualises perception of visual scenes in terms of competition among multiple representations - such as colors, individuals, or objects. Selective visual attention acts to 'bias' this competition in favour of certain selected features or representations. For example, imagine that you are waiting at a busy train station for a friend who is wearing a red coat. You are able to selectively narrow the focus of your attention to search for red objects, in the hope of identifying your friend. Desimone and Duncan argue that the brain achieves this by selectively increasing the gain of neurons responsive to the color red, such that output from these neurons is more likely to reach a downstream processing stage
Information processing
Information processing is the change of information in any manner detectable by an observer. As such, it is a process which describes everything which happens in the universe, from the falling of a rock to the printing of a text file from a digital computer system...
, and, as a consequence, to guide behaviour. According to Miller and Cohen, this selective attention mechanism is in fact just a special case of cognitive control - one in which the biasing occurs in the sensory domain. According to Miller and Cohen's model, the PFC can exert control over input (sensory) or output (response) neuron
Neuron
A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...
s, as well as over assemblies involved in memory
Memory
In psychology, memory is an organism's ability to store, retain, and recall information and experiences. Traditional studies of memory began in the fields of philosophy, including techniques of artificially enhancing memory....
, or emotion
Emotion
Emotion is a complex psychophysiological experience of an individual's state of mind as interacting with biochemical and environmental influences. In humans, emotion fundamentally involves "physiological arousal, expressive behaviors, and conscious experience." Emotion is associated with mood,...
. Cognitive control is mediated by reciprocal PFC connectivity
Functional integration
Functional integration is a collection of results in mathematics and physics where the domain of an integral is no longer a region of space, but a space of functions...
with the sensory
Sensory cortex
The sensory cortex can refer informally to the primary somatosensory cortex, or it can be used as an umbrella term for the primary and secondary cortices of the different senses : the visual cortex on the occipital lobes, the auditory cortex on the temporal lobes, the primary olfactory cortex on...
and motor cortices
Motor cortex
Motor cortex is a term that describes regions of the cerebral cortex involved in the planning, control, and execution of voluntary motor functions.-Anatomy of the motor cortex :The motor cortex can be divided into four main parts:...
, and with the limbic system
Limbic system
The limbic system is a set of brain structures including the hippocampus, amygdala, anterior thalamic nuclei, septum, limbic cortex and fornix, which seemingly support a variety of functions including emotion, behavior, long term memory, and olfaction. The term "limbic" comes from the Latin...
. Within their approach, thus, the term 'cognitive control' is applied to any situation where a biasing signal is used to promote task-appropriate responding, and control thus becomes a crucial component of a wide range of psychological constructs such as selective attention, error monitoring, decision-making, memory inhibition
Memory inhibition
In psychology, memory inhibition is the ability not to remember irrelevant information. Memory inhibition is a critical component of an effective memory system. For example, imagine if, when a person tried to remember where he had parked his car, every place he had ever parked his car came to mind;...
, and response inhibition.
Miyake and Friedman’s Model of Executive Functions
Miyake and Friedman’s theory of executive functions proposes that there are three aspects of executive functions (EF): updating, inhibition, and shifting. A cornerstone of this theoretical framework is the understanding that individual differences in executive functions reflect both unity (i.e., common EF skills) and diversity of each component (e.g., shifting-specific). In other words, aspects of updating, inhibition, and shifting are related, yet each remains a distinct entity. First, updating is defined as the continuous monitoring and quick addition or deletion of contents within one’s working memory. Second, inhibition is one’s capacity to supersede responses that are prepotent in a given situation. Third, shifting is one’s cognitive flexibility to switch between different tasks or mental states.Miyake and Friedman also suggest that the current body of research in executive functions suggest four general conclusions about these skills. The first conclusion is the unity and diversity aspects of executive functions. Second, recent studies suggest that much of one’s EF skills are inherited genetically, as demonstrated in twin studies. Third, clean measures of executive functions can differentiate between normal and clinical or regulatory behaviors, such as ADHD. Last, longitudinal studies demonstrate that EF skills are relatively stable throughout development.
Experimental evidence
The executive system has been traditionally quite hard to define, mainly due to what psychologist Paul W. Burgess calls a lack of "process-behaviour correspondence". That is, there is no single behavior that can in itself be tied to executive function, or indeed executive dysfunction. For example, it is quite obvious what reading-impaired patients cannot do, but it is not so obvious what exactly executive-impaired patients might be incapable of.This is largely due to the nature of the executive system itself. It is mainly concerned with the dynamic, "online" co-ordination of cognitive resources, and, hence, its effect can be observed only by measuring other cognitive processes. In similar manner, it does not always fully engage outside of real-world situations. As neurologist
Neurologist
A neurologist is a physician who specializes in neurology, and is trained to investigate, or diagnose and treat neurological disorders.Neurology is the medical specialty related to the human nervous system. The nervous system encompasses the brain, spinal cord, and peripheral nerves. A specialist...
Antonio Damasio
Antonio Damasio
Antonio Damasio is David Dornsife Professor of Neuroscience at the University of Southern California, where he heads USC's Brain and Creativity Institute and Adjunct Professor at the Salk Institute. Prior to taking up his posts at USC, in 2005, Damasio was M.W...
has reported, a patient with severe day-to-day executive problems may still pass paper-and-pencil or lab-based tests of executive function.
Theories of the executive system were largely driven by observations of patients having suffered frontal lobe
Frontal lobe
The frontal lobe is an area in the brain of humans and other mammals, located at the front of each cerebral hemisphere and positioned anterior to the parietal lobe and superior and anterior to the temporal lobes...
damage. They exhibited disorganized actions and strategies for everyday tasks (a group of behaviors now known as dysexecutive syndrome
Dysexecutive syndrome
Dysexecutive syndrome consists of a group of symptoms, usually resulting from brain damage, that fall into cognitive, behavioural and emotional categories and tend to occur together. The term was introduced by Alan Baddeley to describe a common pattern of dysfunction in executive functions, such...
) although they seemed to perform normally when clinical or lab-based tests were used to assess more fundamental cognitive functions such as memory
Memory
In psychology, memory is an organism's ability to store, retain, and recall information and experiences. Traditional studies of memory began in the fields of philosophy, including techniques of artificially enhancing memory....
, learning
Learning
Learning is acquiring new or modifying existing knowledge, behaviors, skills, values, or preferences and may involve synthesizing different types of information. The ability to learn is possessed by humans, animals and some machines. Progress over time tends to follow learning curves.Human learning...
, language
Language
Language may refer either to the specifically human capacity for acquiring and using complex systems of communication, or to a specific instance of such a system of complex communication...
, and reasoning. It was hypothesized that, to explain this unusual behaviour, there must be an overarching system that co-ordinates other cognitive resources.
Much of the experimental evidence for the neural structures involved in executive functions comes from laboratory tasks such as the Stroop task
Stroop effect
Purple Blue Purple----Blue Purple RedGreen Purple Green----the Stroop effect refers to the fact that naming the color of the first set of words is easier and quicker than the second....
or the Wisconsin Card Sorting Task (WCST). In the Stroop task, for example, human subjects are asked to name the color that color words are printed in when the ink color and word meaning often conflict (for example, the word "RED" in green ink). Executive functions are needed to perform this task, as the relatively overlearned and automatic behaviour (word reading) has to be inhibited in favour of a less practiced task - naming the ink color. Recent functional neuroimaging
Functional neuroimaging
Functional neuroimaging is the use of neuroimaging technology to measure an aspect of brain function, often with a view to understanding the relationship between activity in certain brain areas and specific mental functions...
studies have shown that two parts of the PFC, the anterior cingulate cortex
Anterior cingulate cortex
The anterior cingulate cortex is the frontal part of the cingulate cortex, that resembles a "collar" form around the corpus callosum, the fibrous bundle that relays neural signals between the right and left cerebral hemispheres of the brain...
(ACC) and the dorsolateral prefrontal cortex
Prefrontal cortex
The prefrontal cortex is the anterior part of the frontal lobes of the brain, lying in front of the motor and premotor areas.This brain region has been implicated in planning complex cognitive behaviors, personality expression, decision making and moderating correct social behavior...
(DLPFC), are thought to be particularly important for performing this task.
Context-sensitivity of PFC neurons
Other evidence for the involvement of the PFC in executive functions comes from single-cell electrophysiologyElectrophysiology
Electrophysiology is the study of the electrical properties of biological cells and tissues. It involves measurements of voltage change or electric current on a wide variety of scales from single ion channel proteins to whole organs like the heart...
studies in non-human primate
Primate
A primate is a mammal of the order Primates , which contains prosimians and simians. Primates arose from ancestors that lived in the trees of tropical forests; many primate characteristics represent adaptations to life in this challenging three-dimensional environment...
s, such as the macaque
Macaque
The macaques constitute a genus of Old World monkeys of the subfamily Cercopithecinae. - Description :Aside from humans , the macaques are the most widespread primate genus, ranging from Japan to Afghanistan and, in the case of the barbary macaque, to North Africa...
monkey, which have shown that (in contrast to cells in the posterior brain) many PFC neurons are sensitive to a conjunction of a stimulus and a context. For example, PFC cells might respond to a green cue in a condition where that cue signals that a leftwards fast movement of an eye, head should be made, but not to a green cue in another experimental context. This is important, because the optimal deployment of executive functions is invariably context-dependent. To quote an example offered by Miller and Cohen, a US resident might have an overlearned response to look left when crossing the road. However, when the "context" indicates that he or she is in the UK
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
, this response would have to be suppressed in favour of a different stimulus-response pairing (look right when crossing the road). This behavioural repertoire clearly requires a neural system that is able to integrate the stimulus (the road) with a context (US, UK) to cue a behaviour (look left, look right). Current evidence suggests that neurons in the PFC appear to represent precisely this sort of information. Other evidence from single-cell electrophysiology
Electrophysiology
Electrophysiology is the study of the electrical properties of biological cells and tissues. It involves measurements of voltage change or electric current on a wide variety of scales from single ion channel proteins to whole organs like the heart...
in monkeys implicates ventrolateral PFC (inferior prefrontal convexity) in the control of motor responses. For example, cells that increase their firing rate to NoGo signals as well as a signal that says "don't look there!" have been identified.
Attentional biasing in sensory regions
ElectrophysiologyElectrophysiology
Electrophysiology is the study of the electrical properties of biological cells and tissues. It involves measurements of voltage change or electric current on a wide variety of scales from single ion channel proteins to whole organs like the heart...
and functional neuroimaging
Functional neuroimaging
Functional neuroimaging is the use of neuroimaging technology to measure an aspect of brain function, often with a view to understanding the relationship between activity in certain brain areas and specific mental functions...
studies involving human
Human
Humans are the only living species in the Homo genus...
subjects have been used to describe the neural mechanisms underlying attentional biasing. Most studies have looked for activation at the 'sites' of biasing, such as in the visual
Visual cortex
The visual cortex of the brain is the part of the cerebral cortex responsible for processing visual information. It is located in the occipital lobe, in the back of the brain....
or auditory cortices. Early studies employed event-related potential
Event-related potential
An event-related potential is any measured brain response that is directly the result of a thought or perception. More formally, it is any stereotyped electrophysiological response to an internal or external stimulus....
s to reveal that electrical brain responses recorded over left and right visual cortex are enhanced when the subject is instructed to attend to the appropriate (contralateral) side of space.
The advent of bloodflow-based neuroimaging techniques such as functional magnetic resonance imaging
Functional magnetic resonance imaging
Functional magnetic resonance imaging or functional MRI is a type of specialized MRI scan used to measure the hemodynamic response related to neural activity in the brain or spinal cord of humans or other animals. It is one of the most recently developed forms of neuroimaging...
(fMRI) and positron emission tomography
Positron emission tomography
Positron emission tomography is nuclear medicine imaging technique that produces a three-dimensional image or picture of functional processes in the body. The system detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide , which is introduced into the body on a...
(PET) has more recently permitted the demonstration that neural activity in a number of sensory regions, including color-, motion-, and face-responsive
Face perception
Face perception is the process by which the brain and mind understand and interpret the face, particularly the human face.The human face's proportions and expressions are important to identify origin, emotional tendencies, health qualities, and some social information. From birth, faces are...
regions of visual cortex, is enhanced when subjects are directed to attend to that dimension of a stimulus, suggestive of gain control
Gain
In electronics, gain is a measure of the ability of a circuit to increase the power or amplitude of a signal from the input to the output. It is usually defined as the mean ratio of the signal output of a system to the signal input of the same system. It may also be defined on a logarithmic scale,...
in sensory neocortex. For example, in a typical study, Liu and coworkers presented subjects with arrays of dots moving to the left or right, presented in either red or green. Preceding each stimulus, an instruction cue indicated whether subjects should respond on the basis of the colour or the direction of the dots. Even though colour and motion were present in all stimulus arrays, fMRI activity in colour-sensitive regions (V4) was enhanced when subjects were instructed to attend to the colour, and activity in motion-sensitive regions was increased when subjects were cued to attend to the direction of motion. Several studies have also reported evidence for the biasing signal prior to stimulus onset, with the observation that regions of the frontal cortex tend to come active prior to the onset of an expected stimulus.
Connectivity between the PFC and sensory regions
Despite the growing currency of the 'biasing' model of executive functions, direct evidence for functional connectivity between the PFC and sensory regions when executive functions are used, is to date rather sparse. Indeed, the only direct evidence comes from studies in which a portion of frontal cortex is damaged, and a corresponding effect is observed far from the lesion site, in the responses of sensory neurons. However, few studies have explored whether this effect is specific to situations where executive functions are required. Other methods for measuring connectivity between distant brain regions, such as correlation in the fMRI response, have yielded indirect evidence that the frontal cortex and sensory regions communicate during a variety of processes thought to engage executive functions, such as working memory, but more research is required to establish how information flows between the PFC and the rest of the brain when executive functions are used.Bilingualism & Executive Functions
A growing body of research demonstrates that bilinguals show advantages in executive functions, specifically inhibitory control and task switching. A possible explanation for this is that speaking two languages requires controlling one's attention and choosing the correct language to speak. Across development, bilingual babies , children , and elderly are showing a bilingual advantage when it comes to executive functioning. Interestingly, bimodal bilinguals, or people who speak one language and also know sign language, do not demonstrate this bilingual advantage in executive functioning tasks . This may be because they are not required to actively inhibit one language in order to speak the other.Bilingual individuals also seem to have an advantage in an area known as conflict processing, which occurs when there are multiple representations of one particular response (for example, a word in one language and its translation in the individual’s other language) . The lateral prefrontal cortex has been shown to be involved with conflict processing specifically.
More recent contributions
Other important evidence for executive functions processes in the prefrontal cortex have been described. One widely-cited review article emphasizes the role of the medial part of the PFC in situations where executive functions are likely to be engaged – for example, where it is important to detect errors, identify situations where stimulus conflict may arise, make decisions under uncertainty, or when a reduced probability of obtaining favourable performance outcomes is detected. This review, like many others, highlights interactions between medial and lateral PFCPrefrontal cortex
The prefrontal cortex is the anterior part of the frontal lobes of the brain, lying in front of the motor and premotor areas.This brain region has been implicated in planning complex cognitive behaviors, personality expression, decision making and moderating correct social behavior...
, whereby posterior medial frontal cortex signals the need for increased executive functions and sends this signal on to areas in dorsolateral prefrontal cortex that actually implement control. Yet there has been no compelling evidence at all that this view is correct, and, indeed, one article showed that patients with lateral PFC damage had reduced ERNs (a putative sign of dorsomedial monitoring/error-feedback) - suggesting, if anything, that the direction of flow of the control could be in the reverse direction. Another prominent theory emphasises that interactions along the perpendicular axis of the frontal cortex, arguing that a 'cascade' of interactions between anterior PFC, dorsolateral PFC, and premotor cortex
Premotor cortex
The premotor cortex is an area of motor cortex lying within the frontal lobe of the brain. It extends 3 mm anterior to the primary motor cortex, near the Sylvian fissure, before narrowing to approximately 1 mm near the medial longitudinal fissure, which serves as the posterior border for...
guides behaviour in accordance with past context, present context, and current sensorimotor associations, respectively.
Advances in neuroimaging
Neuroimaging
Neuroimaging includes the use of various techniques to either directly or indirectly image the structure, function/pharmacology of the brain...
techniques have allowed studies of genetic links to executive functions, with the goal of using the imaging techniques as potential endophenotype
Endophenotype
Endophenotype is a psychiatric concept and a special kind of biomarker. The purpose of the concept is to divide behavioral symptoms into more stable phenotypes with a clear genetic connection...
s for discovering the genetic causes of executive function.
See also
- Cognitive neuropsychologyCognitive neuropsychologyCognitive neuropsychology is a branch of cognitive psychology that aims to understand how the structure and function of the brain relates to specific psychological processes. It places a particular emphasis on studying the cognitive effects of brain injury or neurological illness with a view to...
- MetacognitionMetacognitionMetacognition is defined as "cognition about cognition", or "knowing about knowing." It can take many forms; it includes knowledge about when and how to use particular strategies for learning or for problem solving...
- Nonverbal learning disorderNonverbal learning disorderA nonverbal learning disorder or nonverbal learning disability is a condition characterized by a significant discrepancy between higher verbal and lower motor, visuo-spatial, and social skills on an IQ test...
- Self controlSelf controlSelf control is the ability to control one's emotions, behavior and desires in order to obtain some reward later. In psychology it is sometimes called self-regulation...