To fully appreciate how traumatic stress and everyday stress affect a person mentally and physically, it’s important to first understand some basics about the human brain. 

A good place to start is by learning the differences between the two hemispheres of the brain, the so-called right brain and left brain. While the popular distinction between the two is a bit simplified, neuroscientists have found that each hemisphere tends to specialize in different functions. When somebody says they are more “right-brained than left-brained,” this is generally what they mean:

• • Right Brain — The right hemisphere specializes in emotional, intuitive, and spatial processing. Many of its structures lead the regulation and production of emotions via hormone stimulation. It is also heavily involved in storing sensory memories involving sound, touch, and smell. 

• • Left Brain — The left hemisphere specializes in language, analytical thinking, and reasoning. It is heavily involved in planning, communication, and conscious thought. The memories it stores are more likely to involve facts, statistics, and vocabulary. 

People who claim to be more “right-brained” tend to be emotional, intuitive, or artistic. Those who claim to be “left-brained” tend to describe themselves as logical and analytical. Brain imaging studies of people with PTSD have shown that recalling traumatic memories lights up the right hemisphere while decreasing activity in important language areas of the left hemisphere. This helps explain why it can be so hard for trauma survivors to put their experiences into words — parts of the left hemisphere that control linguistics and communication literally become less active. In order for a trauma survivor to talk about their past, their emotional brain has to calm down. This is only possible if they feel safe and comfortable in their environment. 

Another helpful way to understand the left-brain, right-brain concept is to think of each respective hemisphere as the emotional brain and rational brain. Here are some additional basic differences between the two:

• • Emotional Brain — Our unconscious, automatic brain. Through its regulation of our hormones and emotions, it expresses itself through physical reactions in the body, such as a knot in the stomach, a pounding heart, fast and shallow breathing, or feelings of heartbreak.
    
    
  • Rational Brain (Executive Brain) — Our conscious brain. It expresses itself through our deliberate thought, planning, and decision-making. 

The brain develops from the bottom-up, beginning with many of the structures that make up our emotional brain. Some of the key players in our emotional brain include: 

• • Brain Stem — This is the oldest part of the brain, which is why it is sometimes called our “reptilian brain.” It develops in the womb and works immediately after birth. The brain stem is responsible for most of our very basic housekeeping functions, including breathing, eating, regulating feelings of hunger and satiation, pooping, peering, and much more.

• • Limbic System — The limbic system is home to many of the brain’s threat-detection structures and is heavily involved in generating our emotions and regulating hormones. When we face danger, different parts of the limbic system work together to activate our fight-or-flight response. Below is a look at how it does that:
    • Thalamus: The Cook — Think of the thalamus as “the cook.” Sensory information from our environment comes to the thalamus through our eyes, nose, ears, and skin. It takes this incoming information and “blends” all of our sensory perceptions into a “soup” that tells us, “This is happening to me.” It then passes this information on in two different directions: down to the amygdala (another part of the limbic system) and up to the frontal lobes (our conscious awareness). Interestingly, neuroscientists have found that people who have been traumatized often have a hyper-sensitive thalamus. As a result, they tend to be unusually sensitive to everyday sights, sounds, smells, and other sensations in their environment. 
    • Amygdala: The Smoke Detector — Think of the amygdala as “the smoke detector.” One of the star players in our fight-or-flight response, its main job is to identify whether incoming information from the thalamus is relevant to our survival. In other words, it essentially acts as the fear center of our brain by determining whether a sound, image, or body sensation represents a danger to us. If the amygdala determines that we are indeed facing a threat, it acts like a smoke alarm by sending an alert to the hypothalamus and brain stem.
    • The Hypothalamus, Pituitary Gland, and Brain Stem — After receiving an alert from the amygdala, the hypothalamus activates the body’s stress response. It commands the pituitary gland to secrete a cascade of stress hormones like adrenaline and cortisol. At the same time, it tells the brain stem to activate the automatic nervous system (ANS), which increases our heart rate, blood pressure, and breathing rate. Together, the stress hormones and ANS organize a whole-body response to combat the threat. 

As this process makes clear, the emotional brain is constantly scanning our environment for danger and opportunity. When it detects a potential threat, it alerts the rest of the body by releasing hormones and activating the ANS. The resulting physical sensations (e.g. queasiness, butterflies, a racing heart) are designed to get you moving in a different direction. Because the amygdala receives information from the thalamus faster than the frontal lobes, the emotional brain often decides whether or not something is a threat before we are even consciously aware of the danger. 

When it comes to understanding how trauma fits into all of this, many survivors have a smoke detector (amygdala) that is constantly going off. As a result, their stress hormones are consistently higher than the average person, causing them to be agitated, anxious, and on edge much of the time. Their brain has a really hard time telling if a situation is dangerous or not because their smoke detector has become overly sensitive and doesn’t work quite right. They become chronically scared that people hate them, are judging them, or are out to get them. Their energy is so consumed by fighting off unseen enemies that they have very little room for connection, care, and love.

Now let’s look at the rational brain, also known as the executive brain. The rational brain is our conscious thinking mind, and it expresses itself through deliberate thought. Some basic components of the rational brain include:

• • Frontal Lobes — The frontal lobes, located behind the forehead, make up most of our rational brain, or neocortex. Unlike the automatic emotional brain, the frontal lobes of the rational brain enable us to use language and reason, absorb and integrate huge amounts of information, and make choices. They also make planning, creativity, empathy, and self-control possible.
    
    
  • Medial Prefrontal Cortex: The Watchtower — The medial prefrontal cortex (MPFC) is part of the frontal lobes, and it can be thought of as “the watchtower.” If there is smoke in your house, your amygdala will detect the danger and organize a whole-body fight-or-flight response, but it doesn’t determine what’s actually happening. The MPFC, or the watchtower, does this. Although the thalamus sends sensory information to both the amygdala and the frontal lobes, it reaches the amygdala first. This brief head start allows the emotional brain to react before the rational brain has had time to fully evaluate the situation. This helps explain why people sometimes have emotional outbursts — the emotional brain gets the information first. However, as long as the watchtower is functioning well, most people are able to regulate those emotional impulses before acting on them.

As mentioned earlier, brain scans of trauma survivors often show that the rational brain becomes much less active while experiencing, or reliving, traumatic events. The MPFC watchtower is one of those regions of the rational brain that shows decreased activity. With their watchtower weakened, many trauma survivors become dominated by their amygdala and the rest of their emotional brain. Their smoke detector and watchtower become out of balance, making it very difficult for them to regulate emotions, think clearly, and control impulses. Contributing to this imbalance is the fact that when the limbic system activates, the communication pathways between the emotional and rational brain basically get zapped. In brain imaging studies, the amygdala lights up while many language and executive functioning areas of the left hemisphere — including the MPFC watchtower — go dark. 

Understanding this communication breakdown between the rational and emotional brain helps us make sense of a few common real-world scenarios:

• • It explains why there is little sense in arguing with someone who is in a highly emotional state; people struggle to think rationally when they’re flooded with stress hormones like adrenaline and cortisol
  • It explains why public speaking is so difficult when you are nervous; your amygdala signals danger, stress hormones are released, heart rate and blood pressure increase, and the language centers of your left brain shut down. This is why it’s hard to think, remember, and physically speak while you’re up there.
  • It explains why it can be very hard to think and speak clearly experiencing — or reliving — a life-or-death situation; for many people, the language centers of their left brain literally shut down in these moments
  • It explains why people can’t think rationally when they are in love with someone who is off-limits; they are dominated by their emotional brain and communication with their rational brain isn’t strong
  • It explains why a manager who fears their superior may become excessively anxious and paranoid about any task that might involve that individual; their smoke detector is constantly firing off, making it much harder to think rationally and objectively

This battle in the brain ultimately plays out in the body as well. The two are connected. Strong feelings of discomfort in the body — for example, a pit of anxiety in your stomach — are the result of discomfort in the mind. As the author writes: “When our emotional and rational brains are in conflict, (as when we are enraged with someone we love, frightened by someone we depend on, or lust after someone who is off-limits), a tug of war ensues. This war is largely played out in the theater of visceral experience — your gut, your heart, your lungs — and will lead to both physical discomfort and psychological misery.”

Finally, memory and emotion are closely linked as well. In general, the stronger the emotions you feel during an experience, the better you will remember it. Scientists have shown that the more adrenaline you secrete during an event, the more precise and long-lasting the memory will be. This helps explain why many trauma survivors have such detailed and vivid memories of the abuse they suffered.