In the last post, we looked at some of the areas in the brain where stress reactions occur, and their interactions during a typical acute stress reaction. Now, we examine disordered stress, and the changes reflected in brain signaling.
What are the disorders of stress response?
Acute Stress Disorder (ASD):
An acute (2 days – 4 weeks) experience of the below symptoms, within a month of experiencing a severe trauma (defined as a situation where one witnessed or experienced something very distressing, a loss of control over traumatic circumstances, the possibility of losing one’s life, and similar.)
Post-traumatic Stress Disorder (PTSD):
A more chronic, lasting experience of those symptoms compared to ASD.
Generalized categories of symptoms:
Avoidance of related memory triggers, general numbing of feelings
Hyperarousal (increased vigilance of surroundings, for example)
Symptoms disrupt normal day-to-day function
**A note: this is not intended to be medical advice, nor should it be taken as such. If you are concerned about any medical condition you think you may have, please contact your doctor for professional advice.
Many of us start to think of military veterans coming home from conflicts overseas when the topic of PTSD comes up. Indeed, that is a serious issue facing returning soldiers coming back to their lives at home and it deserves every ounce of the attention it gets. But I also want to take a moment to point out that PTSD is not just for people who have seen combat. Roughly 7% of the general US population lives with PTSD, which can arise from car accidents, incidents of violence, childhood abuse, and many other experiences one can have without even leaving one’s hometown. So this is something that could potentially affect anyone.
Adaptations in the brain
As I've probably mentioned more than enough times, stress disorders represent an adaptation to survive a tremendously stressful situation, without the re-adaptation back to a usual level of stress reactivity afterward. The result is a continued stress response even after the context/reason for stress has ended. Recall that we’re talking about 3 major brain areas that interact during a stress response, but also that these are not the ONLY brain areas that are involved.
We have the amygdala (the fear/emotion responder), the hippocampus (event memory), and the prefrontal cortex (behavioral control) interacting to produce a response to aid in avoiding/escaping a harmful situation. Normally, these three areas work together to help you get out of a bad situation and then resume normal function. But this isn’t always the case. Sometimes the brain over-responds and doesn’t adapt back to typical function so easily.
Normally, we have this nice little response as diagrammed below. The amygdala responds to fearful/emotional cues in the environment, and that triggers some strongly encoded memories of the event in the hippocampus. The hippocampus and amygdala responses to stress dampen the behavioral inhibition from the prefrontal cortex. Hopefully very soon thereafter, you've escaped from whatever stressor was threatening you, and usual function resumes.
But in ASD or PTSD, the brain’s adaptation to the environment doesn’t resume usual function, and the result is that fear/emotion area has adapted to be especially responsive. Meanwhile, the other two arms of the circuit are weakened. The representative balance between the three brain regions we're looking at here changes to this:
Where the amygdala is less inhibited and fires more, it alters the timing of neurons firing in the hippocampus, which makes for weaker encoding of new memories and weaker inputs to the PFC. The reduced inhibition from the PFC lets the amygdala continue firing more, which relays to the hippocampus, and further reduces the inhibitory signal coming from the PFC. The checks and balances between the three regions are weakened substantially. At this point, reminders of the event trigger an inordinately strong emotional reaction in this signaling pathway, while "un-learning" or extinction learning is weakened. This reaction results in some of the symptoms of stress disorders- a reminder triggering the sense of re-living the event, for instance. Of course, there are other brain areas contributing here, and I don't want to discount them. But this is a pretty substantial shift of normal signaling!
But just because a signaling pathway in the brain is adapted to work differently from normal doesn't mean it is permanent. There are some treatments available now and others coming up that might provide help and support for people who are dealing with ASD or PTSD. We'll take a look at some of those next time.