Monday, November 17, 2008

Executive Function and ADHD

"Executive Functions" are brain processes that control other brain processes. Specific tasks that involve sensory functions, movement, perception, preparation for action, etc. are organized, regulated, and controlled by higher-order circuits in the brain. We liken executive functions to those of an executive or CEO in a big corporation, or to the general at the rear of the battlefield or the conductor of a symphony. He or she does not personally sell, do the accounting, collect receipts, schedule the airline flights, do the advertising for the company, or go out on patrol or dig the trenches. (Perhaps the occasional conductor such as Leonard Bernstein will play the piano while also conducting; some CEO's or conductors are genius enough to multi-task at times.) But the CEO makes the major decisions and policy programs for the company, does the strategic planning, and selects the managers who design and carry out specific tactics. The CEO initiates programs, plans the strategies, monitors the progress, and evaluates the outcomes. The CEO adapts and changes the program as new circumstances require. But the CEO is vulnerable. If the secretary is absent for a day, scheduling is hampered, monitoring is suspended, and there may be a temporary loss of control. The CEO is effectively brain-dead as far as the momentary functions of the corporation are concerned. Of course, a good hierarchy always includes trustworthy backups, 3-star generals, or first violins who can take over in an emergency. So too in the brain; not all executive functions are vested in a single overall Director, and it is the redundancy of the developed brain that carries on under temporary emergency conditions. For example, fMRI brain imaging shows that when one of the major executive functions carried out in the anterior cingulate (an area of the brain involved in regulating attention) is impaired in an ADHD adult, the functions are apparently transferred to lateral areas of the brain not typically designed for those functions, perhaps with some loss of proficiency but enough to allow continued overall processing to continue. So executive functions are powerful functions, mainly located in the newer areas of the brain (the frontal lobes, both orbital and lateral areas) that include such processes as working memory, inhibition of motor response, and selective attention). Many observers of ADHD have proposed that these Executive Functions are the primary processes that define ADHD. They argue that the ability to plan, organize, initiate and complete tasks, monitor the results of actions, inhibit impulse, regulate time requirements such as being on time or estimating the time to do things, and a host of other functions are the hallmark of ADHD; in fact constitute the primary deficits of ADHD. But does evidence really support this appealing idea? There are several reasons why I think not.
  • First of all. there is the problem that the very definition of what constitutes executive functions varies from one authority to another; there is no standard or accepted definition.
  • When parents or teachers fill out checklists or ratings of executive functions, there appears to be agreement with standard definitions of ADHD (e.g. with DSM-IV clinical symptom definitions), but there is no relationship to executive functions as measured by actual cognitive functions measured in performance tests. (For instance, tests of working memory do not agree with ratings of memory performance.
  • Impairment of executive functions is common in many disorders other than ADHD, for example anxiety, depression, psychosis, etc. In fact, executive dysfunction cuts across almost all mental disorders and cognitive impairments. It would thus appear to be more a consequence of disorders than a specific cause of disorders.
  • Finally, a number of investigations fail to find the executive dysfunctions postulated for ADHD.

For these reasons I believe that while it is useful to assess executive functions in ADHD, particularly since these functions may be trainable and coachable, a full assessment of ADHD requires a much broader range of symptoms and diagnostic criteria.

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