Fear Conditioning & Hypervigilance

Lesson objective:

In this lesson, we learn about PTSD and the role of norepinephrine in the process of fear conditioning during the development of PTSD symptoms

Earlier, we discussed the various effects of chronic stress in the body and the brain.

Similarly, trauma can lead to specific changes in the brain and the body, many of which are similar to the effects of chronic stress. 

These changes can culminate in specific disorders like post-traumatic stress disorder (or PTSD) that require the diagnosis of a clinical professional, but really can lead to a host of changes and unwanted disturbances that can interfere with daily life, even if the current frameworks used by doctors and therapists don’t classify them as a “disorder.” What’s important here is getting a clear look at why some of these changes occur, about what is going on in the brain and body that may lead to the symptoms mentioned, as well as others we don’t mention. 

As we explore how trauma affects the brain and body,  we will start with the hormones which play a role in our response to trauma.

Our responses to stress, fear, and threat, are influenced by various neurochemicals and hormones, including adrenaline, testosterone, cortisol, norepinephrine, and others, some of which we mentioned. 

These neurochemicals are always present in the brain to help regulate emotional response, and specifically to regulate how we respond to situations of stress or fear.

The neurochemical that we will focus on here is norepinephrine

It is a hormone that helps coordinate the whole stress and fear response process.

Simply, norepinephrine helps you pay attention and quickly focus on and respond to short-term stressors. It is responsible for arousal and stimulation in the presence of the many stimuli in the world around you. It activates the HPA axis by exciting or signaling to the hypothalamus. 

Basically, norepinephrine wakes the hypothalamus up after interpreting an incoming threat or stress signal, helping coordinate the response. 

Specifically, norepinephrine plays an important role in two aspects of our response to trauma that go on to influence how we operate after trauma. These are (1) fear conditioning and (2) sustaining hypervigilance.

When you are in a stressful situation and your stress response is active, norepinephrine opens channels of information from the amygdala and other lower brain regions. When it does this, it temporarily reduces the flow of information that comes in from the prefrontal cortex.

In other words, norepinephrine makes sure you’re paying attention to learning from the stressful situation, while suppressing prefrontal cortical function including analytical thinking, cognitive focus, self-control, and sustained attention. 

In this way, norepinephrine contributes to what we call fear conditioning, which is a process by which we make strong associations and rapidly-recalled memories with incidents that were threatening, stressful, or scary. 

This is the biology behind what we talked about earlier with triggers, and the formation of triggers. 

In times of stress, elevated norepinephrine makes sure we remember those moments of fear and what we felt during them.  Simply, incidents that evoke fear are remembered a specific way, more so than other events that happened around the same time. Keeping a tight and close memory of potentially threatening events is an efficient way for the brain to keep you alive. 

Importantly, when our brains associate specific instances or moments with stress and fear, we tend to associate the entire situation with fear, not just the specific aspects of it that were stressful. In other words, because one aspect of an event scared us, other environmental aspects of that event may also be coded as fearful. The sight of a color that you saw, or a particular smell that was present on the day of a stressful or traumatic event signals to the predictive brain that the trauma might be returning. 

In most cases, it is simply a false alarm, or a predictive error. 

But in a world of potential risks, the brain generally errs on the side of caution. And even in the case of predictive errors, the brain might construct a vivid re-experience, or flashback, and your body may have the same response it had in the original situation.

These two steps, 1) fear conditioning and 2) predictive associations, collaborate to cause elaborate flashbacks in the aftermath of trauma. 

The trigger, even if a false alarm, is a sensory input that activates some or all of the same feelings and sensations experienced during the traumatic event. For individuals who have experienced trauma, triggers and trauma reminders may be present all around them. As such, they might be constantly alert, or nearly constantly reliving the feelings of terror they first felt during the traumatic event. And in a search for relief, individuals may try to avoid any and all triggers. So, this process of fear conditioning helps explain re-experiencing and flashbacks which are so common after trauma. 

And the second symptom we recalled earlier–hypervigilance–relies on a similar process. Stay tuned.