Neural Pathways of Stress and Anxiety

“I’ve lived through some terrible things in my life, some of which actually happened”

-Mark Twain

Imagine: it’s approximately 100,000 years ago and you’re sitting around with your fellow friends and family - when a lion suddenly lunges from the bushes. You immediately feel your automatic sympathetic nervous system (Fight/Flight/Freeze response) spring into action resulting in a rapid heart beat, profuse sweating, shorter breaths, your ability to think clearly with your prefrontal cortex subsides, the limbic system highly activates, the Hypothalamic-Pituitary-Adrenal Axis pumps out hormones that increase the availability of glucose (sugar) in your blood and initiate vasodilation throughout your skeletal muscles to increase the flow of blood and vasoconstriction throughout other organs, slowing down digestive, immune, and sexual functions. In other words, initiating the Fight/Flight/Freeze response. As discussed in the previous lecture, all of these ancient neural and hormonal pathways for the stress response evolved to facilitate our survival - they helped keep our ancestors alive during times of real danger. Fast forward to modern day - we still have these same systems, but now they are triggered by stressors, perceived or real, that are not life-threatening - a traffic jam, an argument with a colleague or friend, a story on the news, an upcoming exam or term paper. They can even ambush us, seemingly out of nowhere. Our modern life can feel as if it is a constant source of stressors, activating the same Fight/Flight/Freeze system that kept our ancestors alive under much harsher conditions. In this lecture, we’ll go over a short explanation of neural mechanisms behind the sympathetic/parasympathetic nervous system, to better understand how our body functions during times of stress/anxiety/depression, so that we may retune our reactions to stressors into a more positive and skillful response. 

To begin, it’s important to know how the parasympathetic nervous system (PSNS) acts in conjunction with the sympathetic nervous system. The PSNS is our “rest and digest” system - enabling slower heartbeats, activating our digestive, immune, and sexual systems. The PSNS is dominant when we are safe and relaxed. However, it is important to note we must let ourselves feel safe and relaxed in order to enhance the activation of this system, thus knowing the important difference between an actual stressful experience and an imagined one.

The balance of SNS and PSNS activation is controlled by both conscious processes involving the cerebral cortex (which help with logic, planning, and slow thinking), and subcortical (automatic) circuits that are rapid and subconscious (and help with rapid responses to keep us safe). Let’s say you’re biking on campus, and you round a corner a little too fast - you notice another biker moments before you clash. Just like the ancient neural mechanisms of your ancestors, you perceive danger through both conscious circuits involving the cerebral cortex, and unconscious circuits involving more deep lying neural structures. Your fast-reacting circuits will signal the amygdala (important for emotional responses), light up the limbic system (central to managing psychological functions, such as memory and attention, to emotional stimuli), and send signals shooting through the hypothalamus (a homeostasis regulator that is intermediary between the prefrontal cortex and outside world) to the pituitary glands which finally signal the adrenal glands sitting on top of your kidneys, releasing several types of stress hormones into your bloodstream to prepare your body for action.  Meanwhile, your conscious cortical circuits will process the situation, form memories and associations, and try to steer you towards safety - both in the moment, and the next time you ride your bike.

As explained in the previous lecture, the conditioned illusions of our minds can also create the feeling/anxiety of danger when there isn’t any. For example, perhaps the next time you think of riding your bike, you feel anxious and nervous owing to the association with your crash. Or perhaps you think of an upcoming presentation to your class and feel nervous and anxious because of your conditioned fear of public speaking (perhaps that kindergarten show-and-tell didn’t go so well - or at not so well in your mind!). These cognitive processes and conscious thoughts can activate the same stress/anxiety systems that are activated by clear and present danger. It’s important to note, however, that these essential functions are acting under one large alarm system. An alarm system’s function is to alert our body into action in an attempt to help us in what the alarm system perceives to be a threatening situation - even if it isn’t. Sometimes when experiencing anxiety, we feel there is a foreign attack on our body we cannot escape. We might even conclude that there is something inherently wrong with us, leading to emotions such as shame or anger. So next time you feel the alarm system blaring during imagined threats or associations, it is helpful to remind yourself of how these systems operate. The alarm is trying to help you, not hurt you. Be inquisitive and honest. Is this alarm valid? Or is it simply an association that I have acquired through my experience or from my family and my culture? Most importantly, be ruthlessly compassionate and understanding with yourself through the entire process. We hope that learning the basics of how your body functions under stress can help you better manage it.  In future lectures, we will discuss mechanisms for managing stress and anxiety, such as meditation, mindfulness-based stress reduction, and cognitive behavioral therapy.