Let's talk about the article "Behavioral models of impulsivity in relation to ADHD: Translation between clinical and preclinical studies" (Clinical Psychology Review, 2006).
For some reason, it ranks at the top of Google for “ADHD impulsivity”. Let’s assume this is because, over the last 20 years, scientists have not made much progress in understanding this topic.
Impulsivity can be useful
Healthy impulsivity is good, the authors write, as it helps you seize opportunities. Unhealthy impulsivity, however, is bad, as it leads to decisions you regret.
Impulsivity occurs not only with ADHD
Impulsivity, they write, occurs with ADHD, but not exclusively. It also occurs in mania, addictions, and personality disorders (note from me: for example, borderline personality disorder).
Impulsivity comes in two types, not one
According to the article, there are two types of impulsivity: impulsive action (cannot stop what I have started in time) and impulsive choice (cannot wait for more later, I take less now). These are different problems. Different parts of the brain are responsible for them.
According to the article, you can show that there are two types of impulsivity by conducting two different tests:
- a test for the presence of a brake in the head while performing an action (Go/No-Go and Stop-Signal)
- a test for making decisions whose benefits come in the future (Delay Discounting)
Using these tests, you can see that one person may have only one type of impulsivity, or may have both.
This means they do not necessarily occur together, which indicates that different brain areas are responsible for them.
Note from the article: in some cases, people with “impulsive choice” type of impulsivity can still wait longer if they have no choice.
Therefore, the answer to the question on impulsivity for people with ADHD isn’t so simple
Maybe their problem isn't impulsivity itself, but that they pathologically hate waiting (delay-aversion). That’s why we need to fix that problem, not impulsivity as such.
Thus, the problem is not impulsivity and stupidity (they understand the math), but rather rationality. They are escaping from unbearable pain, the torture of a waiting situation.
Practical benefit of this conclusion
The fact that impulsivity in ADHD patients varies apparently depends on whether they have the first type of impulsivity, the second type, or both.
Therefore, different strategies are needed for each of the two types of impulsivity.
So how do we, ordinary readers, use this conclusion?
- If we cannot wait for future rewards and prefer to get something now, then it is difficult for us to do long-term things in the hope of a bright future. Consequently, we need to learn to break tasks into short steps with frequent rewards. We think in this direction.
- If we cannot stop ourselves, we need to train our brakes, such as counting to ten and similar techniques.
Different areas of the brain are responsible for different types of impulsivity
Problems with impulsivity should be looked for in several specific brain regions. They are most likely there, not one hundred percent, but with high probability.
The first type of impulsivity, action inhibition, is controlled by:
- dorsal prefrontal cortex (upper posterior part of the frontal lobes)
- right inferior frontal gyrus (right lower part of the frontal lobes)
- basal ganglia (deep subcortical structures, especially the caudate nucleus and medial striatum)
The second type of impulsivity, choice, is controlled by:
- orbitofrontal cortex, OFC (lower anterior part of the frontal lobes)
- ventromedial prefrontal cortex (lower middle part of the frontal lobes)
- basolateral amygdala (part of the amygdala deep in the temporal lobes)
All of this was known before them.
Some areas may be responsible for both types:
- ventral striatum (nucleus accumbens)
- subthalamic nucleus
This is what the authors hypothesize.
How did they determine that the prefrontal cortex and basal ganglia are responsible for impulsivity?
The authors say: there are 2 TYPES of evidence that poor inhibition in ADHD children is connected to the prefrontal cortex and basal ganglia.
- Functional MRI shows glowing images of where neurons are active during task performance in the brain's gray matter. The authors of the article remind us, citing other works, that if you do a functional MRI on healthy children and children with ADHD during a special test for the ability to inhibit impulsive action (go/no-go), then two brain zones (basal ganglia and prefrontal cortex) light up differently in children with ADHD than in typical children (abnormally according to them, atypically).
- Data from patients with brain damage (injuries, strokes, diseases) in these areas show that they also have poor inhibition on the so-called stop-signal test and symptoms similar to ADHD (inattentiveness, impulsivity).
The authors hypothesize: since physical brain damage (for example, injuries or diseases) causes both types of impulsivity, and since functional MRI shows that in children with ADHD these same areas work abnormally, it's possible (they're not certain!) that impulsivity (including in ADHD) arises from problems in these areas and the connections between them (although it's unknown what specifically, unless in a particular patient it's a brain injury or disease that the doctor knows about and can say, "this is why you have ADHD").
Impulsivity due to serotonin deficiency?
Interestingly, according to the article, impulsivity in general can be caused by serotonin deficiency. When serotonin is low, people become more impulsive.
This is shown by experiments, where serotonin was lowered and impulsivity increased, and by treatment, where SSRIs, antidepressants that increase serotonin, reduced impulsivity in gambling, sexual addiction, and personality disorders.
However, with ADHD this does not work. SSRIs do not help. This means that impulsivity in ADHD is not due to serotonin deficiency. This is despite the fact that serotonin neurons are physically connected to dopamine neurons. The connection is bidirectional and occurs through synapses.
Serotonin affects dopamine in some way. The balance between them may be important, but the nature of the interaction between serotonin and dopamine is unclear, as is the nature of the interaction between dopamine and serotonin in controlling impulsive behavior. According to the authors of the article, all of this requires further research.
Since amphetamine, which affects these brain areas through dopamine, helps with impulsivity, it is possible that other methods of affecting these areas, such as medication, training, or stimulation, could also help. This requires testing.
Finally, the article says the root cause of ADHD is still a mystery (as of 2006). We know which brain areas are involved, what chemicals are off, what symptoms show up and what treatments work, but we don't know why it happens, what kicks it off, or why some people get it and others don't.
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