Zelazo & Müller (2011). Executive function in typical and atypical development.” – Article summary

Executive function (EF) refers to the psychological processes involved in the conscious control of thought and action. However, there are several possible definitions:

• Executive function corresponds to planning (1), decision making (2), judgement (3) and self-perception (4).
• Executive function corresponds to inhibitory control.
• Executive function refers to a cognitive module consisting of effector output elements involving inhibition, working memory and organisational strategies necessary to prepare a response (i.e. homunculus approach).

It may be that executive function consists of separable but related constructs. It seems to consist of inhibition of prepotent responses (1), shifting between mental sets (i.e. flexibility) (2) and updating and monitoring of representations in working memory (3). However, by conducting a task which is aimed at a single construct of EF, it is unclear whether it taps into multiple component processes (e.g. does flexibility rely on inhibitory control or are they separate constructs).

Executive function has several developmental characteristics:

• It emerges first in early development, around a year of age.
• It develop across a wide range of ages (e.g. important changes between 2 and 5 years; adult-like function around 12 years; some changes continuing into adulthood).
• Failures in executive function occur in different situations at different ages and this depends on the complexity of the situation.
• There are ‘hot’ aspects (e.g. ventral and medial parts of prefrontal cortex) and ‘cool’ aspects of executive function (e.g. lateral prefrontal cortex).
• Difficulties with executive function may be a consequence of perturbations of the epigenetic process.
• Different developmental disorders involve impairments in different aspects of EF.

Luria states that the prefrontal cortex consists of interactive functional systems which involve the integration of subsystems. The subsystems have specific roles but cannot be considered outside of the larger systems. This means that executive function may be a function and not a mechanism or cognitive structure. Functions refer to behavioural constructs defined in terms of their outcome (e.g. what they accomplish). It is possible to organize functionally distinct phases around the constant outcome of solving a problem (i.e. the outcome of EF).

Intending refers to keeping a plan in mind to control behaviour. Rule use refers to translating a plan into action. After acting, evaluation occurs and this includes error detection and error correction. Representational inflexibility refers to the inability to form a new plan. Lack of response control refers to the inability to carry out a new plan.

Executive function draws on the prefrontal cortex but it is not the same. Damage to the PFC does not necessarily mean executive function impairment. The prefrontal cortex includes the orbitofrontal cortex (1), dorsomedial cortex (2), ventrolateral cortex (3), dorsolateral cortex (4) and rostrolateral prefrontal cortices (5).

The lateral prefrontal cortex may play an important role in the integration of sensory and mnemonic information and the regulation of intellectual function and action. It is connected to the thalamus (1), parts of the basal ganglia (2) , the hippocampus (3) and primary and secondary association areas of neocortex (4). Dopamine may play an important role in the lateral prefrontal cortex.

The ventral and medial prefrontal cortex consists of ventral and medial regions of prefrontal cortex. It has strong connections to the amygdala and other parts of the limbic system. It is well suited for the integration of affective and non-affective information and for the regulation of appetitive and motivated behaviour.

It was first believed that PFC was not functional during childhood but this idea has been refuted. The consequences of PFC lesions in children are less noticeable than in adults. Behavioural impairments as a result of PFC lesions may occur later in development when late-developing functions would normally appear. Identical lesions can have different consequences at different ages.

The development of PFC follows increases in head circumference (1), interhemispheric connectivity (2), myelination (3), synaptic density (4), cortical thickness (5) and scalp electrical activity (6). There are several trends in the development of PFC:

• Age-related increases in white-matter volume are monotonic.
• Grey-matter volume in PFC shows an inverted U-shaped pattern.
• These patterns are more pronounced for boys than for girls.
• OFC function develops more rapidly in males and is under hormonal control.
• There is a shift from more diffuse to more focal activation of PFC during performance.

Perseveration refers to continuing with behaviour that should have been inhibited and this characterizes a lot of failures of executive function. Executive function that only depends on an inhibition mechanism is problematic for several reasons:

1. Inhibition difficulties depend on the situation (e.g. A not B or card-sorting task).
2. Inhibition is not a unitary construct (i.e. it consists of multiple parts).
3. Inhibition may be too simple to capture everything covered by executive function (e.g. planning with minimal inhibitory demands).
4. Inhibition does not explain why correct responses are issued but only why actions are not executed.

Interference control refers to the suppression of interference due to stimulus competition. Behavioural inhibition refers to the suppression of a prepotent response. Inhibition may be necessary but not sufficient for executive function.

It is also possible that changes in executive function are the result of changes to the capacity of working memory. This theory holds that development of executive function is the result of increases in the strength of active memory representations. This allows children to override prepotent tendencies mediated by latent memory traces. Executive function may also require both working memory and inhibition.

The cognitive complexity and control theory states that age-related changes in executive function are the result of increases in the hierarchical complexity of the rules that children can formulate, maintain in working memory and use when solving problems. This thus holds that children’s plans correspond literally to rules. Over the course of development, this rule system then gets more complex. Lateral PFC-mediated reprocessing allows reflecting on simple rules and formulate higher-order rules that control the application of the simpler rules. This theory requires the ability to engage in reflection. This typically develops during preschool years.

Basic limbic system functions can be described as the four F’s (i.e. feeding; fleeing; fighting; sexual activity). Cool EF is elicited by abstract, decontextualized problems. Hot EF is required for problems that are characterized by high affective involvement or demand flexible appraisals of the affective significance of stimuli. The somatic marker theory states that the orbitofrontal cortex is required for processing learned associations between affective reactions and specific scenarios (e.g. losing with gambling should elicit a negative feeling). Hot EF appears to develop over the preschool period.

Decision making is normally biased in an adaptive fashion by physiological reactions that predict rewards and punishment (i.e. combining hot and cool functions of EF). On the other hand, it may also be useful to reconceptualize affective problems in a neutral, decontextualized term. As hot and cool EF work together, it is not possible to clearly differentiate between them in a task.

In the problem solving framework, executive function is believed to proceed from problem representation (1) to planning (2) to execution (3) to evaluation (4). Inflexibility can occur at each of these stages:

1. Problem representation
   Cool measures of problem representation include the Flexible Item Selection Task or insight problems (i.e. flexible restructuring of the problem representation). Hot measures include theory of mind measures (i.e.  inter- and intrapersonal perspective taking involves flexible evaluation of the significance of a situation). Children become better in both hot and cold tasks of problem representation with age.
2. Planning
   Cool measures of planning include tasks that only require planning and no other difficulties (e.g. execution). This includes the Tower of Hanoi. Children become better at these tasks with age (e.g. they can remember longer and more complex moves). There are developmental changes in problem analysis and depth of search for a solution. There are also changes in pre-schoolers’ planning when it comes to hot EF.
3. Execution
   Children of 2.5 years make perseverative errors. Three year olds have difficulty integrating incompatible pairs of rules into a single system via higher-order rules despite having knowledge of the rules. Children may be better at a hot EF task when they convert it into a cool EF task (e.g. think about the abstract qualities of the preferred reward instead of the concrete qualities in a delay of gratification task). Three year olds typically have difficulty regulating approach behaviour in motivationally significant situations but are capable of adaptive decision making. Self-regulation may be facilitated by adopting a third-person perspective of one’s behaviour. Children may use symbols to decontextualize concrete stimuli (i.e. creating psychological distance from the stimuli). This may foster reflection and control.
4. Evaluation
   This includes error detection and error correction. Children may develop error detection sooner than error correction in some situations. Younger children may recognize the illogic of extinction behaviour (e.g. persevering while extinction should occur) and are able to detect errors but have difficulty in using this information to control their behaviour.

It is likely that the phases of the problem-solving framework develop together. If task difficulty is equal, hot tasks of EF may be more difficult than cool tasks of EF. There seems to be a strong relation between cool EF and theory of mind. This does not fit with other theories of ToM.

Difficulties with executive function are prominent in a lot of disorders with childhood onset (e.g. autism; conduct disorder; OCD; ADHD).