Stress and Memory

There you are, standing in front of the audience and you suddenly feel a wave of stress rise up inside you. An array of physiological sensations like a racing heart, sweaty palms and a churning in your stomach start to uncontrollably manifest themselves. And all whilst you are trying to give the impression that you are feeling cool, calm and collected.

A stressed-out body.

These are the physical feelings of stress which take place in your body. They are mediated through two channels – a fast route which involves the hypothalamus in your brain activating your adrenaline pathways, and a slower axis which uses hormones as messengers – the hypothalamic-pituitary-adrenal (HPA) axis.

They are both linked to your body’s “fight or flight” response caused by the activation of your sympathetic nervous system – part of your autonomic nervous system – which is involved in readying your body for action. Stress, therefore, isn’t simply mediated by cortisol (although this is a major stress hormone amongst other roles) but also includes a whole host of other chemical factors which each have their unique role in orchestrating the experience of being stressed.

When your memory goes blank.

But there is another intriguing symptom of being stressed out that you might have also experienced – the fact that is can cause your memory to fail. Your mind goes momentary blank, and you are left verbally stumbling whilst trying to remember what you were meant to be saying, or unable to answer a question posed by someone in the audience – an answer that in another less stressful situation you would easily have been able to provide.

This is because stress doesn’t just affect your body, it affects your brain in a way which goes beyond the emotion of “feeling stressed”. And numerous studies published over the past decade or so have revealed that there is one region of the brain which is particularly susceptible to stress – your hippocampus.

Your hippocampus

Your hippocampus is a seahorse-shaped structure in your brain which is often said to be part of your limbic network – a set of regions which are implicated in emotional and memory processes (amongst others). It is your hippocampus which helps you to remember events in your life – so-called “episodic memory” – like last year’s Christmas, that holiday you went on a few months ago, or what you did last night. It also is involved in spatial memory – the type of memory that helps you to navigate around your physical world and explains why London taxi drivers have a larger hippocampus than average.

Glutamate  vs Glucocorticoids

The anatomy and chemistry of your hippocampus is complex, but one of the main neurotransmitters that it uses to orchestrate its neural signalling is called glutamate – the main excitatory neurochemical in the brain. When you experience mild stress, then it can actually be a good thing for your hippocampus as it can promote the process of synaptic plasticity at these glutamate synapses, which in turn helps you to learn and remember better. But when that stress goes beyond a particular threshold, then it starts to have the opposite effect, and you become forgetful.

This is because the glucocorticoids – the chemicals which mediate the stress response in your brain and body – can negatively interfere with glutamate signalling in the hippocampus when their concentration becomes too high. Although the mechanisms of this interaction are highly complex and still not fully understood, the general consensus is that glucocorticoids can cause an unwanted increase in the level of glutamate which interferes with signalling at the synaptic connections between nearby brain cells, causing them to not work as well as they should – hence causing a failure in your memory retrieval.

Although the kind of stress we are talking about here is acute stress, these effects get amplified in the case of severe chronic stress. For example, under chronic stress, there are structural changes to the neurons such as atrophy of the dendritic spines which help to form synaptic connections between brain cells, as well as an increased risk that the levels of glutamate in the hippocampus reach neurotoxic levels.

It’s not all about forgetting.

But there is more to the memory blanking effect than this. Because, from a survival perspective, it is also quite useful that the brain remembers a highly stressful experience so that it can try and avoid it again in the future. The difference between whether the stress makes you remember or forget seems to come down to a matter of timing (although again this isn’t 100% understood). For example, if the stress occurs when your neurons are in a particular phase of learning – something called long-term potentiation where there is a strengthening of connections between individual neurons  – then it causes your brain to remember the event better. However, if the stress occurs before or after this long-term potentiation – or LTP for short – then it can negatively interfere with your neural signalling and cause your memory retrieval to fail. What’s more, science suggests that the effects of stress on your ability to remember can be quite long-lasting (e.g. from 25-90 minutes after the stress) whilst your cortisol levels are still elevated, and only recovering once your cortisol has started to near its baseline levels.

Beyond the hippocampus 

Of course, stress affects more than your hippocampus, it also affects a part of your brain called the prefrontal cortex which is involved in all sorts of “higher thinking” executive functions such as decision-making, problem-solving and inhibition, and explains why stress also has an impact on these types of cognitive processes as well,  like sometimes causing you to make poor  decisions.

Regulating your stress response.

Although stress is something that we all experience from time to time, chronic stress is known to be bad for your health and well-being. And although stressful experiences won’t ever disappear from our lives, the way we deal with the stress is something that can be controlled. For example, a recent study showed how an 8 week Mindfulness Based Stress Reduction training programme resulted in observable functional and structural changes in the brain which were associated with better emotional regulation towards stress.

Working in advance to put the necessary thought processes in place which will help you to manage your stress ”in the moment”, is, therefore, one effective strategy for helping to ensure that you can indeed be cool, calm and collected in body, and brain.

If you would like to find out more about the impact of your emotions on you thinking then please get in touch with Synaptic Potential.

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