5 things you need to know about how stress affects your brain.

Image via iStock. By Dr Paula Watkins, clinical psychologist and meditation expert. Compiled by Shelly Horton. 

Firstly, not all stress is bad. We know that a healthy amount of stress can increase performance. Think of the nervous energy that an athlete needs to get focused and sharp to get off the block fast – that’s performing enhancing stress.

But what we know is that stress reaches tipping point – we often call it the fight-or-flight response. It’s the brain’s activation of our sympathetic nervous system which initiates a series of changes that we experience in our mind and body.

This system in our body is very old and evolved to serve our ancestors at time when the stressors that humans faced were pretty different to those that we commonly experience today.

1. Stress increases heart rate and also changes where our blood is predominantly going to in the body.

When the brain is in a stressed state it prioritises getting blood to organs and muscles that our ancestors needed when they encountered stress. So we see an increase in blood flow to the lungs, brain and large muscle such as legs and arms as well as the sense organs – our eyes, our ears, our nose.

Related: 16 people on the techniques they use to manage their stress.

We only have X-amount of blood in our body at any given time, so more blood to these areas means less to others. During stress the brain deprioritses blood flow the skin – causing us to feel clammy as well as cold hands and feet.

Blood flow to the digestive system is also limited which we can experience as nausea or ‘butterflies in our tummy’, as well as digestive problems, diarrhoea and constipation.

Interestingly, a secondary effect of our digestion having less blood supply is that we produce less saliva which explains why many people experience a dry mouth due to stress and anxiety.

2. Stress Surpasses Logical Thinking

When we’re stressed our brain activates the more primitive and emotional region of our brain – known as our limbic system – more than our more complex higher brain centers.

Our limbic system is the seat of emotion and reaction. When activated during stress, it overrides more rational parts of the brain and suppresses concentration, short-term memory, rational thought, and inhibition. We can act without the regulating effect of wisdom, memory or judgment. Logic is simply unavailable in the moment, and reactions are based on raw emotion.

The biological function of all this allows you to engage fully in fight or flight without your thinking brain intruding and this is good if you’re needing to escape from a predator.

Related: “It almost feels like my entire DNA changed”: Sharon Stone on how her brain injury has affected her life.

Unfortunately for us today, suppression of our rational responses can lead us to take actions we later regret, in the long-term these responses can also harm your memory and impair cognitive function.

3. Stress depletes brain chemicals

If our level of stress is severe or recurrent the chemicals that carry messages from one nerve cell to another can become depleted, and the brain becomes sluggish and inefficient. This can lead to a variety of mental health effects, including:

- Depression
- Sleep disturbances
- Racing thoughts and difficulty concentrating
- Difficulty learning
- Absent-mindedness
- Difficulty making decisions
- Obsessive or compulsive behaviors
- Increased hostility, worry and guilt (post continues after gallery).

4. Stress sharpens your senses but dulls your concentration

When we’re stressed the brain tells our senses to become hyper-alert. The purpose of this is to enable us to scan our environment and respond to danger quickly. Our hyper-vigilance can mean hyper-reactivity to anything that grabs our attention. Our mind can become scattered and racing.

Related: 10 simple tips for creating better mental health this week.

The paradox here is that even though we are – in some ways – more focused than ever before, it’s not in a stable way so we actually unable to concentrate on any one thing, our mind keeps going back to whatever it is that’s stressing us and simultaneously it gets pulled and generally easily irritated by the many, many things that the senses are picking up.

5. Extreme stress can physically change your brain

Structural changes can occur in the brain as a result of severe and chronic stress. In particular the amygdala, which is our panic alarm button alerting the body to stress, can be become more sensitive and even physically larger in size.

Extreme, excessive levels of cortisol can also lead to a shrinking of the hippocampus. The hippocampus is our primary hub for memory and when it decreases in size so too can our memory capacity.

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These very sad effects have been observed in survivors of trauma, war veterans and victims of extreme childhood abuse.