Monday, 8 July 2013

Executive Functions and Attention Deficit Hyperactivity Disorder

Executive function impairment has been traditionally viewed as a part of ADHD. Dr. Thomas E Brown in his new book "A New Understanding of ADHD in Children and Adults: Executive Function Impairments" (released in May, 2013) suggests that Executive Function Disorder (EFD) should be considered a distinct mental disorder. 

ADHD was initially described in medical literature in 1902 as a disruptive behavior disorder. It characterized children who were unable to sit still in class, listen to adults, and who often disrupted their classrooms. Then, as now, ADHD was seen more often in young boys than girls. In 1980, this conceptualization changed to highlight problems with attention as the key aspect of the disorder. Now called Attention Deficit Disorder (ADD), it remained categorized as a behavior disorder, despite the omission of a behavioral descriptor from the name. In 1987, the diagnosis once again placed an equal emphasis on hyperactivity in addition to attention difficulties. In 1994, a subtype that did not have problems with hyperactivity, only attention, was again acknowledged.

Regardless of the name of the disorder or to what extent hyperactivity is considered to be a major symptom, research into cognitive impairments associated with ADHD have discovered that children and adults with ADHD tend to perform less well on measures of executive function than those without the disorder. Executive function refers to the management of the brain's cognitive abilities and is the mechanism by which the brain self-regulates. When this discovery was made, some researchers began to think of ADHD as a disorder primarily of executive function because the symptoms of ADHD can be explained by problems in this area. If the brain is an orchestra, executive function is the conductor. In this perspective, people with ADHD have an incompetent conductor. Yet efforts to conclusively assess executive functions using neuropsychological measures have had mixed results. While groups with ADHD did show impairment on measures of vigilance, working memory, planning and response inhibition, researchers concluded that while these weaknesses were associated with ADHD, they could not be considered a cause. Of course, no correlational study could prove a causal link, but the true problem with these conclusions is that only about 30% of those with ADHD have significant impairments in their executive functioning.

An alternative way of considering the link between executive function and ADHD is that there are clusters of cognitive functions that make up executive functioning. These six clusters are activation, which involves organizing and prioritizing, focusing, which involves maintaining and shifting attention, effort, which involves levels of alertness and processing speeds, emotion, which involves regulating emotion and frustration, memory, which involves utilizing working memory, and action, which involves the monitoring and self-regulation of actions. From this perspective, these executive functions are situationally problematic for those with ADHD. Individuals with ADHD seem to have some areas in which they have no difficulty performing various functions, but may be completely impaired in those same areas in other aspects of life. They often describe it as being related to their personal interest in the subject. Therefore, it is not cognitive functioning itself that is impaired, but rather the systems that turn these functions on and off. If a day-to-day task does not offer some sufficient intrinsic benefit or threat, the cognitive functions are not turned on. Additionally, this perspective does not see ADHD as an all-or-nothing disorder. It is not as simple as having ADHD or not, but it is rather more like depression, which comes and goes.

While these models are significantly divergent from each other, they both attempt to synthesize the understandings of executive functions as a self-regulatory mechanism, as well as describing ADHD as a disorder that involves a problem in the individual's development of their executive functioning. The first perspective sees behavioral inhibition as aspect of executive function that all other functions depend on, and which is defective in those with ADHD. In the second perspective, behavioral inhibition is one of many executive functions that are interdependent and interconnected. All people with ADHD, in both views, have impairment of executive function; it is the essence of the disorder. There is another inherent conflict between these two views based upon how executive function is defined. If it is defined as the set of functions accurately measured by neuropsychological tests, then only a minority of those with ADHD have such impairments. The implication of this conflict is that there needs to be a redefinition of executive functioning. The typical approach in scientific research is to isolate and measure a specific variable, yet this approach is inappropriate for executive function due to its very nature. Instead, tests of executive function for ADHD should involve situations that attempt to replicate real life. 

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