A stressful day?
It was blowing so hard that teenage boys could shave by sticking their head outside and letting the wind blow it off.
My soon to be wife, in the wedding limo, roared past the bus with me and all the guests on board and, whooping, fishtailed out of sight. Then the bus broke down. We were on the side of the road, in the country, 10 miles from the nearest town, and late for my wedding. My fiancée was waiting for us and, having passed us already, didn’t know we’d broken down. She just thought I was late, or worse, that I’d legged it.
Our driver hitched a ride back to the nearby (small) town, nicked a bus from his competition, left a note (we think) and drove off. We redecorated the new bus from the old, and hightailed it to the church. Late. And the wind had knocked the power out. It was otherwise a lovely day.
We’ve been married 17 years now and these, and other memories from our wedding are fresh. Others, like what we ate during the wedding, are vague. You might be the same. Why are these memories fresh, when the day was, by all accounts, stressful?
It’s probably a no-brainer to say that emotional experiences make for strong memories, particularly if they’re emotionally significant – like weddings, childbirth, graduation, loss of a loved one and so on. This holds for pleasant and unpleasant experiences. But what exactly is going on?
Brain bits: Hippocampus
There are some key structures we need to cover off. If you’re new here or, horrors, have forgotten, you can remind yourself about the hippocampus and stress. In short, we concluded that the hippocampus, a critical structure in converting short-term memories to long-term memories, is adversely affected by stress, because stress hormones kill hippocampal brain cells.
Brain bits: Prefrontal cortex
Parts of the prefrontal cortex are also adversely affected. While the cortex covers your brain all over, this bit, the prefrontal cortex, sits at the front of your brain, across your forehead and also up a little. It’s the grey wrinkly bit you’d see if you took that part of your skull off. Cortex comes from the Latin via Greek meaning ‘bark’, as in tree bark. The prefrontal cortex is part of your frontal lobes, where lots of really impressive thinking happens. It’s hungry, but does tricks that let the human brain achieve extraordinary things.
Brain bits: Amygdala
Then there’s the amygdala (a-MIG-da-la), from the Latin meaning almond because, yup, it looks kind of like an almond, in that it’s roughly the same size. But it’s a fascinating little guy. To say that it’s involved in emotion is like saying that Donald Trump thought about real estate once. It’s a true, neural heavyweight in the emotion department.
Now, this doesn’t mean that it’s solely responsible for emotional things. While the brain does regionalize its activity, it’s also incredibly well connected, so it’s a bit of a misnomer to say that all emotion happens here. For example, to make stuff happen, the amygdala communicates with the hypothalamus, the prefrontal cortex, the ventral striatum, the periaqueductal gray (love the sound of that)… and the list goes on.
Now here’s the really interesting bit, which brings some ideas together.
Tying it up: Stress, emotion, memory and the HPA axis
A stressful event causes a cascade of chemicals, thanks mostly to the HPA axis, which is a tricky little circuit we all have, to help us manage stress. The A in HPA stands for Adrenal glands (on the kidneys), which is where the hormones are released from. We’re talking especially here about the longer-lasting stress chemical called cortisol. This interferes with the consolidation of memories, when the stress is emotionally neutral. Cortisol messes up the hippocampus and the prefrontal cortex, so that we don’t remember much of what’s gone on.
But it’s a totally different story when the stress is emotionally colored. When we get stress like this (grief, weddings etc) cortisol activates the amygdala. The interaction between the amygdala and the hippocampus means that we encode and consolidate stuff that’s emotionally charged, but not the stuff that isn’t. Note though, we need the emotional arousal and the stress. The stressful event can be happy, but it needs to put us under stress in some way for cortisol to be released and so enhance memory of the event.
So here’s the take home bit
Now you know why emotionally charged, stressful events are well-remembered, whereas just emotional, or just stressful, events, might not be. There are two systems at work, both differently affected by the stress chemical cortisol.
Can you therefore trust your memory for some events over others? Should we be seeking to add emotional color to things to help us remember? What are the implications for exam study, where it’s stressful but not necessarily emotional, and cortisol may negatively impact memory? Do we emotionally charge the material in some way by putting ourselves in an emotional state?
For people with anxiety disorders, including things like post-traumatic stress disorder, one of the key things is to be able to think about the event without evoking the emotions. Perhaps there’s opportunity to think about how we approach this too.
Impressive words to drop into the morning coffee chat
Amygdala, hippocampus, prefrontal cortex
What do you think?
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