Two top ADHD experts explain how the attention deficit brain works — and, in some cases, why it doesn’t always work at its best.
How do stimulants work in the ADHD brain?
Stimulation is an easily measured feature of the first-line stimulant medications, but it is not clear that stimulation is how and why they work for ADHD. There are 43 medications currently available that stimulate in the same way that amphetamine and methylphenidate do, but only three of those medications make ADHD better. The rest make it worse. Just being a stimulant is not enough to make a medication work in an ADHD brain.
A PET scan study was done monitoring a specially prepared solution of methylphenidate to see where it wound up in the human brain. Everyone expected that it would go to somewhere in the fronto-parietal cortex, or to some area that was rich in adrenaline or dopamine nerves. It didn’t. Instead it was actively pulled out of the blood and concentrated in only one area at the exact centre of the brain called the corpus striatum.
The striatum has no adrenaline or dopamine activity. The striatum is your executive assistant. It scans all of your thoughts, feelings, and experiences and sends the one most important thing up to your cortex for you to think about. Everything else is handled behind the scenes.
The current theory of ADHD is that the striatum works 99 percent as well as it does in neurotypical brains. Rather than sending only one important thing to the frontal cortex, it sends five or six things, with no particular significance attached to any one of them. This is what it is like to have untreated ADHD — five things rumbling about in your head for no apparent reason. The ADHD medications help the striatum work the way it was meant to.
Are stimulants safe for the brain?
Many years ago, people had unfounded fears about the long-term effects on the brain of taking stimulant-class medications every day for a lifetime. We know the answer. The first data come from the use of stimulants for the treatment of a sleep disorder called narcolepsy. Reviews of people who have taken the same medications that are used to treat ADHD every day for 40 to 50 years did not find a single long-term problem. The longest study of ADHD is the Milwaukee Study, now about 28 years old. Thus far, all of the risk of ADHD has been associated with not treating the condition with medication, not with medication treatment itself.
Why don’t methylphenidate or amphetamine work for me or my child?
Through the years, it has been recognized that the right molecule at the right dose for the unique individual child or adult should have dramatic benefits, with essentially no side effects. However, many parents found that their child did not tolerate or benefit from taking the two stimulant medications, methylphenidate (Ritalin, Concerta, and so on) and amphetamine (Adderall, Vyvanse, and so on). We now know why.
It turns out that the dosage ranges approved by the FDA for the first-line stimulant medications work for only about half of patients. Between six to eight percent of people get their optimal response at doses lower than the lowest doses manufactured. If these patients start at the very lowest dose available, they are already overdosed and experience the Zombie syndrome (emotional blunting, lethargy) or the Starbuck’s syndrome (being too revved up, having a rapid heart rate, becoming irritable). The patients do fine when they take lower doses.
Conversely, about 40 percent of people get their optimal response at doses higher than the highest strengths approved by the FDA. They try medication, but they don’t get to a dose that gives them dramatic benefits. The recognition of a wider range of optimal doses has resulted in better medication response for up to half of patients.
Why does the ADHD brain lose interest in tasks?
PET imaging studies of brains in people diagnosed with ADHD demonstrate that chemicals that activate reward-recognizing circuits in the brain tend to bind on significantly fewer receptor sites in people with ADHD than do those in a healthy comparison group. These and other imaging studies may help explain why people with ADHD tend to be less able than their peers to anticipate pleasure or register satisfaction with tasks for which the payoff is delayed. An important effect is that they have great difficulty in activating themselves to get started on tasks that are not especially interesting to them and in sustaining motivation to complete tasks for which the rewards are not imminently available.
Why is the ADHD brain often swamped by emotion?
There are two primary ways in which emotions play a critical role in the chronic difficulties of people with ADHD. Both are related to working memory impairments—the person’s limited capacity to keep in mind and use multiple bits of emotion-laden information at the same time. Sometimes the working memory impairments of the ADHD brain allow a momentary emotion to become too strong; the person is flooded with one emotion and unable to attend to other emotions, facts, and memories relevant to that memory.
At other times, the working memory impairments of ADHD leave the person with insufficient sensitivity to the importance of a particular emotion because he or she hasn’t kept other relevant information sufficiently in mind, or factored it into his or her assessment of the situation.
Why doesn’t the ADHD brain always make the connection?
The networks that carry information related to emotion and other aspects of brain functioning tend to be somewhat more limited in individuals with ADHD compared to most others. Years ago, most scientists thought that impairments of ADHD were due primarily to problems within specific regions of the brain, particularly the prefrontal cortex. New technologies, however, have shown that some of the impairments of people with ADHD may be more related to networks of fibers that support interactive communication between various regions of the brain. One type of communication between brain regions occurs via connections referred to as “white matter.” Imaging studies have shown abnormalities in the structure of white matter in brains of children, adolescents, and adults with ADHD.
Such abnormalities may explain some of the difficulties these individuals have — keeping one thing in mind while doing something else. One study has shown that methylphenidate, used to treat ADHD, can normalize the connectivity limitations in the motivation and reward networks of children with ADHD when they are performing some assigned tasks.