Executive Functions and the Brains Signaling System

Recognition of the amazing fact that executive functions generally operate without conscious awareness offers an important caveat to my use of the orchestra conductor as a metaphor for executive functions. Some might take my metaphor literally and assume that there is a special consciousness in the brain that coordinates other cognitive functions. One might picture a little man, a homunculus, a central executive somewhere behind one's forehead, exercising conscious control over cognition like a miniature Wizard of Oz. Thus, if there is a problem with the orchestra's playing, one might attempt to speak to the conductor, requesting or demanding needed improvements in performance.

Indeed, this presumed "conductor" or controlling consciousness is often the target of encouragement, pleas, and demands by parents, teachers, and others as they attempt to help those who suffer from ADD. "You just need to make yourself focus and pay attention to your schoolwork the way you focus on those video games you love to play!" they say. "You've got to wake up and put the same effort and energy into your studies that you put into playing hockey!"

Those who care about persons with ADD and witness their poor performance in important tasks routinely prod them to deal with their "impotence" in the face of those tasks by insisting: "Just make yourself do it! We can all see that you have the ability. It's just a matter of realizing what is really important and exercising willpower!" Alternatively, they may impose punishments on the person with ADD or shame them for their failure to "make themselves" do consistently what they ought to do. These critics seem to assume that the person with ADD needs only to speak emphatically to the "conductor" of their own mental operations to get the desired results.

But in reality there is no conscious conductor within the human brain. Further, each individual can only use what is made available by his or her own neural networks. If the person's neural networks for executive functions are impaired, as they are in ADD, then that individual is likely to be proportionally impaired in the management of a wide range of cognitive functions regardless of how much he or she may wish otherwise.

There is now considerable evidence that persons appropriately diagnosed with ADD suffer from significant impairments in executive functions of the brain. These functions are not all localized in a single area of the brain; they are decentralized, with many supported by complex networks within the prefrontal cortex. Some essential components of executive functions are supported by the amygdala and other subcortical structures, while other executive functions depend on the reticular formation and portions of the cerebellum located in the posterior of the brain. Figure 3 in Chapter 3 shows these and other critical regions and structures of the brain.

Complex neuronal networks link the various structures in the brain that sustain executive functions. Rapid-fire messages of input and output travel these networks via low-voltage electrical impulses that can traverse the entire system in much less than a millisecond. The efficient movement of these electrical impulses along the network depends on the rapid release and reuptake of neurotransmitter chemicals, which carry each message across synapses, or the connections between neurons, much as a spark jumps the gap of a sparkplug.

To do this work, each of the 100 billion neurons in the brain depends on one of the fifty or so neurotransmitter chemicals manufactured within the brain. Without the effective release and reuptake of the needed neurotransmitter chemical, that portion of the neural network cannot effectively carry its messages. There is now considerable evidence that executive functions of the brain impaired in ADD depend primarily, though not exclusively, on two particular neurotransmitter chemicals: dopamine and norepinephrine.

The most persuasive evidence for the importance of these two transmitter chemicals in ADD impairments comes from medication treatment studies. Over two hundred well-controlled studies have demonstrated effectiveness of stimulant medications in alleviating symptoms of ADHD. Al though these medications are not effective for all persons with ADHD, they work effectively to alleviate ADHD symptoms for 70 to 80 percent of those diagnosed with this disorder. And the medications used to treat ADHD symptoms tend to alleviate many symptoms of ADHD simultaneously.

The primary action of medications used for ADD is to facilitate release and to inhibit reuptake of dopamine and norepinephrine at neural synapses of crucially important executive functions. As Antonio Damasio (1994) emphasized,

Without basic attention and working memory there is no prospect of coherent mental activity. . . . They are necessary for the process of reasoning, during which possible outcomes are compared, ranking of results are established, and inferences are made. (p. 197)

ADD medications help to release dopamine or norepinephrine across the synaptic gap between neurons and to hold it there long enough to pass the message along. Medications that do not act powerfully to facilitate release and to block reuptake of dopamine and norepinephrine tend not to be effective in alleviating ADD symptoms.

Improvement produced by stimulants generally can be seen within thirty to sixty minutes after an effective dose is administered. When the medication has worn off, ADD symptoms generally reappear at their former level. Stimulants thus do not cure ADD symptoms; they only alleviate them while each dose of medication is active. In this sense, taking stimulants is not like taking doses of an antibiotic to wipe out an infection; it is more like wearing eyeglasses that correct one's vision while the glasses are being worn, but do nothing to fix one's impaired eyes. This effect has been demonstrated repeatedly in over two hundred medication treatment studies that were double-blind: that is, neither the doctors nor the patients knew during the study who was being given real stimulant medication and who was being treated with placebos.

Given the often dramatic alleviation of ADD symptoms experienced by 70 to 80 percent of persons diagnosed with ADHD when they take stimulant medications, it is very difficult to sustain the notion that ADHD

impairments are a matter of a lack of willpower. Prior to beginning medication treatment most ADHD patients have made heroic, though often erratic, efforts to improve their situation with willpower alone. Usually such efforts barely work, if at all, and cannot be sustained.

Some argue that improvement in ADD symptoms requires not only willpower, but also intensive behavioral treatments. Results of a major study sponsored by the National Institute of Mental Health (MTA, 1999) challenged this assumption. In the study, 576 children diagnosed with ADHD were randomly assigned to one of four groups, which received either:

Comprehensive behavioral treatment with no medication, Carefully managed medication treatment with no other treatment, A combination of comprehensive behavioral treatment with medication management, or Community treatment with a pediatrician or another caregiver of the family's choice.

The results of this study were striking. Stimulant medication alone, carefully monitored for each child, was of significantly greater help than the best battery of behavioral supports that could be developed without medication. More surprising, children who received the combined treatment (medication and comprehensive behavioral treatment) showed no better improvement of their core ADHD symptoms than did children treated only with carefully managed medications. Combined treatments were more helpful with some related problems, but nonmedication treatments, even at their best, did not improve the core symptoms of ADHD anywhere near as much as did the carefully monitored medication treatment. This study, described with many others in Chapter 9, stands as powerful evidence that impairments of attention and memory associated with ADHD result primarily from malfunctions in parts of the brain's neural networks that depend on the chemicals dopamine and norepinephrine.

Much more remains to be learned about how the brain's complicated neural networks operate to sustain the broad range of functions encompassed in "attention." Yet it is clear that impairments of executive func tions, those brain processes that organize and activate what we generally think of as attention, are not the result of insufficient willpower. So in fact there is an answer to the mystery of inattention illustrated by the experiences of Larry and Monica. Neural chemical impairments of the brain's executive functions cause some individuals who are good at paying attention to specific activities that interest them to have chronic impairment in focusing for many other tasks, despite their wish and intention to do otherwise.

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