Episode 26: Stress and the Brain with Dr. Andrea Wilkinson
What is Stress?
Stress was first defined by Dr. Hans Selye in 1950 as the mind and body’s response to any pressure or demand. Our stress response is also known as our “fight or flight” response. It evolved as a survival mechanism that enabled humans and other mammals to quickly react when faced with a threat or potential threat. In the moment when we are faced with a threatening situation, we must decide to either face it and fight it off, or flea and run away as quickly as possible. As humans evolved, however, we have gone from being stressed by truly life-threatening events – e.g., a predator lurking in the background (such as a lion) that may come and attack us to non-threatening perceived stress that exists more in our interpretation of the event – e.g., traffic jams, work pressure or family challenges.
What are Stressors?
Simply put – a stressor is the thing that stresses you out. It is something that you internally process as a negative.
A stressor can be internal thoughts or external stimuli or event; it is our perception of a stressor that determines if it will kick off a stress response in our body and our brain. Your stress response will be triggered regardless of whether the stressor is real or imagined. Given the role of perception in our experience of stress, what triggers a stress response in one person might not trigger a stress response in another. Needless to say, truly life-threatening events (e.g., a robber entering a bank that you’re in) will trigger a stress response in most individuals – but, traffic (for example) might be perceived and interpreted by the body as stressful for one individual, whereas for another person traffic might be quite relaxing. You can be stressed out solely by a thought. When in fact nothing has happened in the external world – but you still feel stressed. So, stressors can exist solely inside your mind – e.g., feeling over worked.
Why did humans evolve to experience stress at all?
It is important to remember how stress serves us.
Stress isn’t always a bad thing – it can be useful for a burst of energy & focus. Stress in the short-term can enhance memory and performance. For example, if you are about to speak in public – feeling stress can give you the mental and physical energy you need to really knock that public talk out of the park. It can help keep you focused and alert. But, stress can become dangerous when it is experienced continuously. In fact, chronic stress can actually change your brain. Specifically, consistently experiencing stress can affect brain size, its structure and how it functions.
What happens when humans experience stress?
Your stress response begins in your brain, specifically in your Hypothalamic Pituitary Axis (or the H-P-A Axis) and results in a series of interactions that take place between your brain and your body.
When you are experiencing stress:
Your heart starts to beat faster than normal, which increases blood to your muscles
Your breathing speeds up – sending more oxygen to your brain which boosts your level of mental alertness
Glucose (sugar) is released into your bloodstream which gives you more energy
These changes happen so quickly – you have no conscious awareness of them; but, they are all meant to increase your chances of survival by giving you extra energy and mental focus to get out of the stressful situation. When you encounter a stressful situation (like a bear in nature or a traffic jam when you are running late for a meeting) your HPA axis is activated and releases your stress hormone (called cortisol). Cortisol primes your body for instant action – giving you energy to physically deal with the stress. It does this by pumping sugar (or glucose) into your bloodstream and releasing adrenaline (hormone released to get us ready to fight or flea a situation) and suppresses bodily functions that are not necessary for your immediate survival (e.g., supresses your immune response and digestion). So, in the short-term stress primes our bodies to get ready to deal with the stress in an effective way, but high levels of cortisol over long periods of time can have a damaging effect on your brain.
Stress & Memory
Chronic, unmanaged stress can negatively impact learning and memory.
As levels of your stress hormone (cortisol) rise, electric signals in your hippocampus (the part of your brain responsible for memory and learning) begin to deteriorate and the size of your hippocampus can even shrink. Your hippocampus helps to control stress levels by controlling/inhibiting your Hypothalamic Pituitary Axis (or the H-P-A Axis), so when the hippocampus is weakened, so is your ability to control your stress. But, not to fear, the negative impact of stress on your hippocampus requires extended stress exposure to occur and research shows that these changes are reversible!
As noted, chronic stress (continuous cortisol) can literally cause your brain to shrink in size.
Too much stress (and cortisol – the stress hormone) can deteriorate the connections between brain cells and lead to shrinking of your frontal lobe (the part of the brain associated with our higher-level thinking, concentration, judgement, decision making and organization). Chronic stress has been associated with fewer neurons being made in the hippocampus. This means that chronic stress might make it harder for you to learn and remember things.
Why is consistent cortisol bad?
Elevated cortisol keeps your heart rate up and elevates your blood pressure
Cortisol promotes the release of glucose in the blood (to increase energy); but, excess energy ultimately becomes stored as fat (eventually leading to hardened arteries and abdominal obesity)
Cortisol also reduces digestion and suppresses your immune system (as mentioned); so, often people who are chronically stressed get sick more often
Cortisol interferes with your circadian rhythm making it hard to sleep and sleep is central for brain health
Cortisol’s job is really to find and produce energy – so it will source energy from wherever it can (e.g., by breaking down some fat); but, a problem with prolonged stress is that the cortisol can even begin to break down some bone.
In a prolonged or exaggerated stress response, cortisol fails to function properly which has also been linked to increased inflammation
Our stress response was built to give us temporary surges of physical and mental energy, but we were never meant to be chronically stressed.
In fact, chronic stress is associated with:
Decreased concentration
Poorer memory
Increased risk of anxiety and depression, sleep disturbances (e.g., insomnia)
Smaller brains – specifically an area of the brain called the hippocampus, which is responsible for learning and memory
Research Studies
Imaging studies have shown a connection between the cortisol levels in your blood and physical changes in the brain. Scanning studies have shown that people with high levels of cortisol (stress hormone) have smaller brains and worse memories – so it is really important that you look for ways to manage your stress levels.
Managing Stress
As mentioned earlier, our experience of stressors (the non life-threatening kind) differs from one person to the next. And we know that experiencing chronic stress is bad for our bodies and our brains; so, how can you go about managing stress?
What can you do to minimize your experience of chronic or consistent stress?
1. Exercise
2. Reduce intake of stimulants (e.g., caffeine, nicotine and sugar)
3. Eat a balanced diet
4. Practice meditation and mindfulness