When we are under stress, a variety of biological processes are taking place. The amygdala activates stress pathways in the brain, and the hypothalamus and the brainstem release high amounts of norepinephrine and dopamine. While these chemicals have a range of effects on the brain, they particularly affect the prefrontal cortex (PFC).
The PFC is the most frontal part of the brain, sitting above our eyes. The PFC plays a major role in planning, higher-order thinking, problem solving, and simulating/anticipating the results of actions we may or may not undertake.
The PFC is also important in “staying on task” despite the presence of potential distractors. When you need to concentrate really hard on a complex math problem, your PFC is highly engaged.
To summarize an incredible amount of work by the likes of Amy Arnsten at Yale University and others (see also), dopamine is thought to be important in repressing the “noise” (distractions) in PFC brain circuits while norepinephrine is believed to enhance the “signal”.
The effects of these two neurotransmitters on the PFC and ultimately behavior follow an inverted-U relationship where too little or too much dopamine or norepinephrine in the PFC leads to sub/supra-optimal functioning of this area of the brain. Thus, an intermediate level of these chemicals is best for optimal PFC function.
Stress increases the levels of dopamine and norepinephrine in the brain
The inverted-U model for the effects of dopamine and norepinephrine on the PFC is important given the fact that stress increases the level of both of these chemicals in this area of the brain. So, the optimal balance of dopamine and norepinephrine may be thrown off under stress.
But, this isn’t the complete story.
Genetics affect dopamine levels in the PFC
COMT is an enzyme that helps to break down dopamine and to regulate its level in the body and brain. Two variations in the COMT gene result in a differential stability of the COMT enzyme, allowing it to more or less efficiently breakdown dopamine. Individuals with variation 1 have higher enzymatic activity and therefore lower levels of dopamine in the PFC. In contrast, variation 2 results in lower COMT activity and therefore higher levels of dopamine in this brain region.
Both variations are quite common in the human population. This suggests both had a useful purpose, evolutionarily. Several studies have demonstrated that individuals with variation 2 perform well in cognitively demanding tasks but have an enhanced vulnerability to stress and wilt under pressure.
In contrast, people with variation 1 have better stress resiliency.
This is thought to be due to the fact individuals with variation 1 have lower dopamine and that the dopamine boost that occurs under stress moves these individuals toward a more optimal level of dopamine for performing cognitively demanding tasks. To further support these points, a large study in Taiwan has shown those individuals with lower dopamine due to COMT variation 1 perform better on a stressful, standardized test administered to 10th graders across the country each year.
And it’s not just an effect on dopamine. Research has shown that individuals with variation 1 show lower physiological stress reactivity than individuals with variation 2.
Are your genes your destiny?
Should those individuals with variation 2 in their COMT gene resign themselves to doing poorly on big standardized tests and wilting under pressure?
The short answer? No. The long answer? We are more than our genetics.
First, our genetics interact with other aspects of our biology to ultimately produce behavior. My own research has shown that COMT genetic variation interacts with age to affect Now vs Later decision making. We interpreted this in context of the inverted-U relationship with dopamine and PFC function as dopamine levels are known to decline with age. So, a particular genetic setup that leads to supra-optimal dopamine levels when one is young may result in more optimal levels as one ages and dopamine “falls” down the curve toward more optimal levels.
Biology is just one part of the equation, though.
The Importance of Mindset
Mindset, or how an individual reacts to the biological changes that accompany stress, is also critical.
It has been shown that having a “stress-is-enhancing” mindset leads to better affective and cognitive outcomes than a “stress-is-debilitating” mindset.
Anyone can take steps to re-frame their stressful experiences to see stress as beneficial rather than detrimental.
For example, treat your stress as something you learn from rather than dwelling on the negative aspects.
Final Thoughts
In closing, genetic variation in dopamine signaling plays a role in how we perform under cognitively demanding tasks. Evolutionarily speaking, it made sense for some people to perform well under pressure while others performed better under baseline, unstressed conditions. We should embrace the genetic diversity inherent in this and other behaviors but also realize biology is only one determinant of behavior. Our mindset and how we frame the effect of stress on us is also critical and, in fact, has biological effects on our stress response.
This, my first Brain & Behavior blog piece, reflects a theme we will encounter throughout our look at the brain and human behavior: behavior is modulated by both our biology and environment. Behavior is complicated and so to understand it, we need to look beyond merely our genes, proteins, and cells. Especially when it comes to human behavior, our environment and experiences affect our biology and behavior. None of these relationships are simple, which is what makes studying them so interesting.
