Stress, Trauma, and the Brain

At their core, brains are organs of adaptation in the service of survival. In the process of evolution as social animals, we have been shaped to stay close to significant others for the safety, resources, and comfort we need to love and work. Autonomic arousal and stress are indicators that we are facing a real or imagined threat to our survival. At low to moderate levels of arousal, what could also be called curiosity, interest, or exploration, stress activates our brains to engage in learning and adaptive behaviors. Hunger pangs, a car drifting into our lane, or an unexpected bill will capture our attention, put us on alert, and signal us to take action. We cope with these challenges by grabbing a bite, honking our horn, or calling our accountant. This is a level of stress within the normal range of experience that signals us to take appropriate action. 

For most of us and for most of the time, we respond to these challenges with minimum disruption. We get knocked down, get up, dust ourselves off, and carry on. We call this resilience, determination, grit, or getting back on the horse that threw you. But this can be taken too far. The spin-offs of machismo, rugged individualism, and denial can, in the long-term, impair our ability to recognize and attend to higher levels of chronic stress and even trauma. For example, veterans are loath to complain or seek psychological help either during or after active duty, choosing to suffer in silence to avoid embarrassment or losing face. Yet they struggle with PTSD and the stressors of post-deployment civilian life, committing suicide at double the rate of civilians. 

In the most general sense, humans have evolved to cope with stress for brief periods of time. There is an optimal range of arousal within which neural plasticity, emotional-regulation, and executive functioning are maintained and optimized. Below this range (in the absence of stimulation or challenge), our brains and bodies slow down to conserve energy and restore themselves. As arousal and stress advance above our optimal range, escalating arousal eventually leads to deficits in brain functioning and psychological well-being. This usually results in the inhibition of brain systems responsible for adaptive and flexible emotional, cognitive, and immunological functioning. These are the trauma-related changes that we work to reverse during treatment. 

At even higher levels of arousal, neural networks can be functionally inhibited, dissociated from one another, and locked into stable patterns of activation that maintain a traumatized state of mind and body. This we call trauma or posttraumatic stress disorder (PTSD). The old saying, “What doesn’t kill you makes you stronger,” only applies within a moderate range of stress; above it, what doesn’t kill you disrupts optimal neural functioning and integration, impairs the bodies restorative and learning capabilities, and ultimately makes you weaker. At a certain level of intensity (different for all of us), stress shifts from a manageable challenge to a state of arousal that triggers a fight, flee, or freeze reaction. Understanding trauma is not a simple matter because its impact depends on our genetics, life history, temperament, culture, personality, and level of social support. This is why the same situation may be taken in stride by one person and result in traumatic reactions and PTSD in another. 

We like to get a clear picture in our minds about complex processes and one that plagued me for years was determining the boundary between stress and trauma. In other words, what is the tipping point that moves us beyond stress and into trauma? Freud, who was very interested in trauma early in his career, used the term “stimulus barrier” to refer to this tipping point. He said that this stimulus barrier allows us to process incoming information up to a certain level of arousal, beyond which our ability to organize our experience is overwhelmed. The result of this overwhelm is shock, terror, or the constellation of symptoms we now, a century later, refer to as PTSD. It is important to remember that while some people are more resistant to stress than others, no one is immune to trauma. Everyone’s defenses have a breaking point, where stress can turn to terror. 

As we explore trauma in the chapters ahead, we will explore the biological, psychological, and social dimensions of what it means to surpass the stimulus barrier. We will explore the biochemical changes which affect our brains, bodies, and minds; the neurodynamic shifts which disrupt cortical and subcortical relationships and make us regress to more primitive mode of behavior; and how these changes in our brains impact both our subjective experience, executive functioning, and our ability to attune to and connect with others. Overall, trauma disrupts our ability to navigate our physical and social worlds in a flexible and coherent manner. The surpassing of the stimulus barrier and the inability of the cortex to coordinate conscious awareness, leave traumatized individuals spinning in a whirlpool of fragmented and overwhelming emotions, sensations, and thoughts.