In psychology and neuroscience, executive dysfunction, or executive function deficit, is a disruption to the efficacy of the executive functions, which is a group of cognitive processes that regulate, control, and manage other cognitive processes. Executive dysfunction can refer to both neurocognitive deficits and behavioural symptoms. It is implicated in numerous neurological and mental disorders, as well as short-term and long-term changes in non-clinical executive control. It can encompass other cognitive difficulties like planning, organizing, initiating tasks, and regulating emotions. It is a core characteristic of attention deficit hyperactivity disorder (ADHD) and can elucidate numerous other recognized symptoms. Extreme executive dysfunction is the cardinal feature of dysexecutive syndrome.
Overview Executive functioning is a theoretical construct representing a domain of cognitive processes that regulate, control, and manage other cognitive processes. Executive functioning is not a unitary concept; it is a broad description of the set of processes involved in certain areas of cognitive and behavioural control. Executive processes are integral to higher brain function, particularly in the areas of goal formation, planning, goal-directed action, self-monitoring, attention, response inhibition, and coordination of complex cognition and motor control for effective performance. Deficits of the executive functions are observed in all populations to varying degrees, but severe executive dysfunction can have devastating effects on cognition and behaviour in both individual and social contexts on a day-to-day basis.
Executive dysfunction does occur to a minor degree in all individuals on both short-term and long-term scales. In non-clinical populations, the activation of executive processes appears to inhibit further activation of the same processes, suggesting a mechanism for normal fluctuations in executive control. Decline in executive functioning is also associated with both normal and clinical aging. The decline of memory processes as people age appears to affect executive functions, which also points to the general role of memory in executive functioning.
Executive dysfunction appears to consistently involve disruptions in task-oriented behavior, which requires executive control in the inhibition of habitual responses and goal activation. Such executive control is responsible for adjusting behaviour to reconcile environmental changes with goals for effective behaviour. Impairments in set shifting ability are a notable feature of executive dysfunction; set shifting is the cognitive ability to dynamically change focus between points of fixation based on changing goals and environmental stimuli. This offers a parsimonious explanation for the common occurrence of impulsive, hyperactive, disorganized, and aggressive behaviour in clinical patients with executive dysfunction. A 2011 study confirms there is a lack of self-control, greater impulsivity, and greater disorganization with executive dysfunction, leading to greater amounts of aggressive behavior.
Executive dysfunction, particularly in working memory capacity, may also lead to varying degrees of emotional dysregulation, which can manifest as chronic depression, anxiety, or hyperemotionality. Russell Barkley proposed a hybrid model of the role of behavioural disinhibition in the presentation of ADHD, which has served as the basis for much research of both ADHD and broader implications of the executive system.
Other common and distinctive symptoms of executive dysfunction include utilization behaviour, which is compulsive manipulation/use of nearby objects due simply to their presence and accessibility (rather than a functional reason); and imitation behaviour, a tendency to rely on imitation as a primary means of social interaction. Research also suggests that executive set shifting is a co-mediator with episodic memory of feeling-of-knowing (FOK) accuracy, such that executive dysfunction may reduce FOK accuracy.
There is some evidence suggesting that executive dysfunction may produce beneficial effects as well as maladaptive ones. Abraham et al. demonstrate that creative thinking in schizophrenia is mediated by executive dysfunction, and they establish a firm etiology for creativity in psychoticism, pinpointing a cognitive preference for broader top-down associative thinking versus goal-oriented thinking, which closely resembles aspects of ADHD. It is postulated that elements of psychosis are present in both ADHD and schizophrenia/schizotypy due to dopamine overlap.
Cause The cause of executive dysfunction is heterogeneous,Nigg JT (2006). What causes ADHD?: Understanding what goes wrong and why. New York, NY: Guilford Press. , . as many neurocognitive processes are involved in the executive system and each may be compromised by a range of genetic and environmental factors. Learning and development of long-term memory play a role in the severity of executive dysfunction through dynamic interaction with neurological characteristics. Studies in cognitive neuroscience suggest that executive functions are widely distributed throughout the brain, though a few areas have been isolated as primary contributors. Executive dysfunction is studied extensively in clinical neuropsychology as well, allowing correlations to be drawn between such dysexecutive symptoms and their neurological correlates. A 2015 study confirmed that executive dysfunction has a positive correlation with neurodevelopmental disorders such as autism spectrum disorder (ASD) or attention deficit hyperactivity disorder (ADHD).
Executive processes are closely integrated with memory retrieval capabilities for overall cognitive control; in particular, goal/task-information is stored in both short-term and long-term memory, and effective performance requires effective storage and retrieval of this information.
Executive dysfunction characterizes many of the symptoms observed in numerous clinical populations. In the case of acquired brain injury and neurodegenerative diseases there is a clear neurological etiology producing dysexecutive symptoms. Conversely, syndromes and disorders are defined and diagnosed based on their symptomatology rather than etiology. Thus, while Parkinson's disease, a neurodegenerative condition, causes executive dysfunction, a disorder such as ADHD is a classification given to a set of subjectively-determined symptoms implicating executive dysfunction – models from the 1990s and 2000s indicate that such clinical symptoms are caused by executive dysfunction.
Neurophysiology Executive functioning is not a unitary concept. Many studies have been conducted in an attempt to pinpoint the exact regions of the brain that lead to executive dysfunction, producing a vast amount of often conflicting information indicating wide and inconsistent distribution of such functions. A common assumption is that disrupted executive control processes are associated with pathology in prefrontal brain regions. This is supported to some extent by the primary literature, which shows both pre-frontal activation and communication between the pre-frontal cortex and other areas associated with executive functions such as the basal ganglia and cerebellum.
In most cases of executive dysfunction, deficits are attributed to either frontal lobe damage or dysfunction, or to disruption in fronto-subcortical connectivity. Neuroimaging with PET and fMRI has confirmed the relationship between executive function and functional frontal pathology. Neuroimaging studies have also suggested that some constituent functions are not discretely localized in prefrontal regions. Functional imaging studies using different tests of executive function have implicated the dorsolateral prefrontal cortex to be the primary site of cortical activation during these tasks. In addition, PET studies of patients with Parkinson's disease have suggested that tests of executive function are associated with abnormal function in the globus pallidus and appear to be the genuine result of basal ganglia damage.
With substantial cognitive load, fMRI signals indicate a common network of frontal, parietal and occipital cortices, thalamus, and the cerebellum. This observation suggests that executive function is mediated by dynamic and flexible networks that are characterized using functional integration and effective connectivity analyses. The complete circuit underlying executive function includes both a direct and an indirect circuit. The neural circuit responsible for executive functioning is, in fact, located primarily in the frontal lobe. This main circuit originates in the dorsolateral prefrontal cortex/orbitofrontal cortex and then projects through the striatum and thalamus to return to the prefrontal cortex.
Not surprisingly, plaques and tangles in the frontal cortex can cause disruption in functions as well as damage to the connections between prefrontal cortex and the hippocampus. Another important point is in the finding that structural MRI images link the severity of white matter lesions to deficits in cognition.
The emerging view suggests that cognitive processes materialize from networks that span multiple cortical sites with closely collaborative and over-lapping functions. A challenge for future research will be to map the multiple brain regions that might combine with each other in a vast number of ways, depending on the task requirements.
Genetics Certain genes have been identified with a clear correlation to executive dysfunction and related psychopathologies. According to Friedman et al. (2008), the heritability of executive functions is among the highest of any psychological trait. The dopamine receptor D4 gene (DRD4) with 7'-repeating polymorphism (7R) has been repeatedly shown to correlate strongly with impulsive response style on psychological tests of executive dysfunction, particularly in clinical ADHD. The catechol-o-methyl transferase gene (COMT) codes for an enzyme that degrades catecholamine neurotransmitters (DA and NE), and its Val158Met polymorphism is linked with the modulation of task-oriented cognition and behavior (including set shifting) and the experience of reward, which are major aspects of executive functioning. COMT is also linked to methylphenidate (stimulant medication) response in children with ADHD. Both the DRD4/7R and COMT/Val158Met polymorphisms are also correlated with executive dysfunction in schizophrenia and schizotypal behaviour.
Evolutionary perspective The prefrontal lobe controls two related executive functioning domains. The first is mediation of abilities involved in planning, problem solving, and understanding information, as well as engaging in working memory processes and controlled attention. In this sense, the prefrontal lobe is involved with dealing with basic, everyday situations, especially those involving metacognitive functions. The second domain involves the ability to fulfill biological needs through the coordination of cognition and emotions which are both associated with the frontal and prefrontal areas.