Stress and Memory

– by Lee Smith, Ph.D.

Chronic stress messes with your mind.

Sitting like tuques atop each of our kidneys are our adrenal glands, which sweat hormones such as cortisol when we’re stressed. Cortisol and its buddies have a huge portfolio of stress related jobs, and one of them is to regulate how we retain and remember things. They can slide across the blood-brain barrier and influence a whole lot of what goes on upstairs.

The research is pretty clear that the cortisol from momentary stress helps with the formation of memory by acting on brain cells. On the other hand, a lot of cortisol from chronic stress does some very bad things to our ability to learn and remember.

Before going further, let’s first have a look at some of the ins and outs, so to speak, of learning and memory. In the brain, learning is largely about strengthening patterns of connections between collections of neurons. Picture the possible patterns of Christmas lights twinkling not just on your house, but throughout your neighbourhood, your city, your country. Learning involves strengthening old and establishing new twinkling patterns.

And here’s some really good news. We’ve learned in more recent years that we normally make new neurons continuously and that this neurogenesis partly supports neuroplasticity and learning. New learning, a stimulating environment and exercise all boost neurogenesis.

So the two big learning processes to keep your eyes on are the making and strengthening of patterns of twinkling connections and the recruitment of new neurons that can twinkle-in as needed.

Acute stress seems to enhance all this precise twinkling very nicely, with cortisol helping to strengthen connections and capitalize on the new recruits.

But wait a minute. I’m not saying that we have to be stressed all the time in order to be at our best for learning. I’m really talking about stress-related learning. If we recall that stress and fear arise under conditions that may be threatening in some way, then a mechanism for super-learning the details around something of life-changing importance is very desirable. Fear conditioning can happen from one encounter and last forever, thanks in part to the boost from stress hormones.

This is why fear conditioning and traumatic memories are so powerfully and durably acquired. Our little brains are full of them.

We might not think that we have any particular memory for emotion. Instead, emotion seems to be some feeling that arises in the present moment, and seems to be faithfully about what is happening in that present moment.

But consider how we can often overreact emotionally to situations and only realize later that we were way out of line. How come!? The ‘way out of line’ is an emotional reaction that was ‘recalled’ inappropriately because the new situation was similar in some way to some old distressing and stress-boosted learning. That we might be sensitive, jealous, offended or even terrified at times when the situation doesn’t really call for those reactions is a reflection of emotional states being ‘recalled’, brought out in an active state, at the wrong but related time. An unhealed broken heart can bring rage or recoil without a second thought.

Now let’s look at chronic stress. When we experience stress frequently, the bath of cortisol harms brain cells and disrupts neurogenesis. Chronic cortisol is toxic to cells in the hippocampus, a brain structure that is crucial for forming new knowledge. Chronic stress can kill neurons in the hippocampus. Moreover, chronic stress also disrupts the formation of new neurons.

In this way, chronic stress damages the brain and impairs our ability to learn, remember and to regulate our emotion. Chronic stress can push neurons to the edge of a cliff, leaving them more vulnerable to being nudged over. Chronic stress may potentially worsen neurological outcomes from stroke, aging and disease.