Stressed out in the brain

Last time, we got started with a discussion of stress reactions and brain adaptations. Now that I’ve covered some of the more general stuff, let’s dive into the neuroscience! Leigh loves the neuroscience.

It’s safe to say that many, many parts of the brain are involved in responding to stressful things. We know a lot, but we don’t know it all. I’m going to focus on the major players in this response, but as always, this is not a comprehensive list (because I’m not writing a book here).

Let’s meet our contestants:

Amygdala- Named after the almond (and most definitely not a part of the built-in dictionary in my word processing program), the amygdala is a whole series of cooperative little nuclei in your brain. Their job is to convey emotional reactions, particularly fear reactions, in response to what’s going on around you. The result puts you on high alert.

Hippocampus- I’ve already proclaimed my love for the hippocampus, but I’ll do it again. This part of your brain is awesome. Among other things, it’s involved in learning associations with places, events, sensory inputs (sounds, sights, etc) and other aspects of experiences and settings. As the hippocampus processes these pieces of information together, you form memories of places and the events that happen in those places. After the associations are made, memory modification through re-consolidation and extinction learning are also going on in the hippocampus.

Prefrontal cortex- Ever had a bad day and managed to restrain yourself from throwing things left and right? Thank your prefrontal cortex. (Unless, of course, you ended up going ahead and throwing things anyway.) Your prefrontal cortex is involved in all sorts of thinking things through: decision-making, calculating consequences of actions, looking to the future. In short, some high-end judgment call processing goes on up there.

The three of these areas have a lot of interconnections! The amygdala outputs affect the hippocampus, outputs from the hippocampus can modify signaling in the prefrontal cortex, which in turn is able to suppress the amygdala. And so on and so forth, creating an extensive set of interactions between these three centers of stress reaction. Each of these areas changes its output in response to inputs from other areas! These responses, in concert with many others taking place during stressful situations, prime us to stay alive under adverse or threatening circumstances.

Figure 1. Like three interconnected peas in a pod. Except, in your brain.

When you're involved in a frightening situation, you observe situational cues that help you to identify that the situation is not a good place to be. Your amygdala helps you to recognize these cues as fearful. The amygdala's response sends signals to the rest of the brain that something strange is going on. Your hippocampus takes up the cue to remember this situation- in case you should ever encounter those circumstances again, you can remember it and stay away from something potentially dangerous. The effects of the hippocampus and amygdala stress responses dampen activity in the prefrontal cortex, lessening its function in suppressing emotional responses during the stress episode. The result is a quick series of brain changes that increase your alertness and help you to dart away from a source of danger.

Stress reactions are a short-term situation most of the time- the body adapts for the duration of the stressful stimulus, and it re-adapts once the need for the stress reaction ends. Unfortunately, things don’t always work like we expect them to. Those homeostatic mechanisms protect us, that increase the likelihood that we get through those stressful situations, can harm us in the long run.

The downside is that sometimes, those system adaptations don’t always make their way back once the need for the stress reaction passes. And that's our topic for next time.