Stress has a major affect on our bodies and our brain. The release of catecholamines (adrenaline and related chemicals) and cortisol causes significant changes throughout our body that are designed to prepare us for “fight or flight.” By shutting down all non-essential functions the stress response system prepares us for a life and death struggle
Nowadays there are no life or death struggles, and the non-essential functions that get shut down are pretty essential to navigating our busy and complex world and include our brain’s ability to think clearly.
I recently ran across an excellent review of the scientific literature on the effects of stress on brain function. This post is a summary of that article.
The effect of stress on brain function is fairly dramatic. In particular, the functioning of the prefrontal cortex (the newest part of the brain, and the part that does most of what we consider “thinking”) is severely impaired by stress.
One way of thinking about why this happens is that, in the past, stress implied the presence of a significant threat. Facing such a threat it was often better to rely on instinct rather than careful analysis (when you are facing a saber-tooth tiger you don’t really have time to think about why the tiger is there).
Nowadays, when we experience stress there is usually no acute threat… we are just dealing with a pressure to perform better at work… or perhaps lose a job. In those situations our thinking ability is essential and so the stress response of the body becomes a problem rather than a solution.
The best studied impairment in brain function is a dramatic decrease in what is called “working memory.” Working memory refers to the brain’s ability to hold many pieces of information in awareness at the same time, without relying on external reminders. A good example of working memory is being able to remember a number (a phone number for instance) without relying on repetition (many people may have to say the number over and over while they dial it, “415-555-8099… 415-555-8099….”).
That is a fairly trivial example of the role of working memory. Working memory is also essential in deciding what the best solution is to a problem with many options (“should I marry Joe or should I go off with Jim… what are the pros and cons?”). With impaired working memory the ability to consider a range of options is reduced and the likelihood of engaging in “black and white thinking” is increased.
Dopamine is a chemical which is involved in many brain functions, including motivation. As an example, most drugs that are abused activate the dopamine system in the emotional or limbic part of the brain which is why there is such and overwhelming motivation (or craving) for drugs.
In the prefrontal cortex, a particular dopamine receptor (dopamine one) plays a key role in allowing us to focus on important information. With too little dopamine one brain cells in the prefrontal cortex aren’t able to turn on when important information comes in (the brain can’t focus because it isn’t active enough).
Too much dopamine one overwhelms the ability of the brain to turn off when irrelevant information comes through (it overwhelms the cooling down function of a key set of receptors called the HCN receptors). The result is that lots of dopamine one also makes it hard to focus, because the brain is over-stimulated by unimportant information.
Stress also overactivates norepinephrine (noradrenaline) circuits and this further reduces the ability of the brain to selectively focus attention.
In summary, there are at least two different ways that neurotransmitters (brain chemicals) that are released by stress causes a non-selective (not just in response to important information) activation of the prefrontal cortex that makes it much harder to focus only on the important information and thus reduces working memory.
Cortisol (the main stress hormone released in the body) plays a role in these effects. It reduces working memory, while at the same time increasing vivid memory. Think of it this way, when you are facing that saber-tooth tiger you better remember everything that happens, your brain shuts down the thinking function (instincts are faster than thoughts) and at the same time turns on a real time recorder of everything that takes place (so that you can learn the important lessons of the encounter).
There is some evidence that we can undo the effects of stress activation in daily life – for example prazosin (a blocker of excessive norepinephrine activation) and guanfacine (an activator of the circuits that help with selective attention) have been shown to help with attention deficit disorder and posttraumatic stress disorder, both conditions with impaired attention.
However, for now these kinds of interventions are experimental. And the best solution to the harmful effects of stress on the brain is to retrain yourself to not activate stress systems when dealing with everyday stressors… Mindfulness and meditation are two of the most effective ways of doing that.
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