Blanking out: How stress can shut down the command centre in the brain
14:32 GMT, 10 April 2012
We've all had those terrible moments, whether just before making a wedding speech or delivering a presentation at work, when our minds have gone completely blank.
Now scientists are one step closer to understanding why we have developed such a counterproductive (and embarrassing) response to stress.
Under pressure: Scientists still don't fully understand why we experience 'brain freezes' during stressful moments
It's long been known that the ancient and primitive part of the brain – called the hypothalamus – reacts to perceived danger by triggering a 'fight or flight' response. It sends a signal to release adrenalin, quickening the heart rate, speeding the breath and preparing us to confront the perceived monster or run away.
However, scientists are now realising that stress can have a huge impact on the prefrontal cortex as well. This is the part of the brain that evolved most recently and doesn't fully develop until after your teenage years.
The prefrontal cortext holds the circuitry we need for abstract thought. It allows us to concentrate on the task at hand while storing useful information in temporary storage for later on. It also prevents you from performing inappropriate actions and is basically the command centre for the brain.
A review in the latest issue of Scientific American looked at a number of studies that showed what makes a person vulnerable to anxiety.
Genetic makeup is one factor as some people have weaker enzymes that are needed to return the brain back to normal functioning after a stressful episode.
Co-author Carolyn Manure added that she had found a relation in her own work between stress exposure and shrinkage in prefrontal grey matter.
The authors also pointed to a study by John Morrison of the Mount Sinai School of Medicine that found prefrontal dendrites (the branches off a neuron) are affected by stress. And while they could regrow if stress disappears they could not rebound after severe stress.
Primed for panic: Early negative experiences of struggling with stress can make people more vulnerable as adults
Why then is this most evolved part of the brain, which is so key to dealing with immediate problems, so sensitive to stress
The review in the Scientific American suggests when under great stress the brain can accidentally flick from its higher cognitive functions to primal reactions as it assumes we need to react instinctively to save ourselves.
'Primitive brain pathways can stop us on a dime or ready us to flee,' Amy Arnsten, Carolyn Mazure and Rjita Sinha wrote.
'These mechanisms may serve a similar function when we face danger in the modern world – say when a reckless driver cuts us off and we need to slam on the brakes.'
However, they said that if we remain in this highly-aroused state prefrontal function weakens.
They said this could be a 'devastating handicap in circumstances where we need to engage in complex decision making about a loved one's serious medical condition or organise an important project to a tight deadline.'
Scientists hope this new understanding will help them develop strategies to keep our neural-control centre intact.
Studies have shown that children who have managed stressful situations well have a built-in resilience to it later in life, while those who have had a difficult experience are more vulnerable to depression and anxiety.
They added that simply learning about how stress affects the brain could help reassure people the next time they have a 'brain freeze.'
For more information see the April 2012 copy of Scientific American