Our Primitive Response to Stress
The fundamental behavior of all organisms is to approach what is life sustaining and avoid that which is dangerous. The success of rapid and accurate approach-avoidance decisions determines if an organism will live to reproduce and carry its genes forward to the next generation or if it will be fated to go not so gently into that good night. The most primitive subcortical fight-or-flight circuitry - shared with our reptilian ancestors - is interwoven with the most highly evolved association areas of the cerebral cortex used to consciously analyze threat. Thus, while there is conscious input during stressful situations, under extreme threat, later evolving emotional and cognitive processes are directed by ancient, rapid acting neural networks fundamental to survival.
The modern human brain reflects millions of years of evolutionary adaptation that embodies compromises between response speed and the flexibility made possible by a larger but slower cortex (Mesulam, 1998). Each neural network reflects elements of this compromise and, like most design compromises, results in functional shortcomings. Evolution is driven and directed by the physical survival of the species, not by the happiness of individuals. Thus, much of the brain's functioning is based upon primitive fight-or-flight mechanisms as opposed to conscious and compassionate decision-making. Because of this, the conscious and unconscious management of fear and anxiety is a core component of our personalities, attachment relationships, and character.
How does evolution make its “choices”? An important example may be seen in the conservation of the primitive deer-in-the-headlights startle response. Think about a time when you were startled: Did you come to an abrupt stop, freeze all of your movements and hold your breath as you scanned the environment for a threat? All of these responses maximize our ability to avoid detection, locate the source of possible danger, and prepare to fight or flee. As sophisticated as language has become, it is still the creation of sound that might give away our location to a potential predator; the freeze response results in the inhibition of language in highly stressful and traumatic situations. Natural selection has shaped the evolution of language, but conserved the freeze rule. When the threat passes, we begin to relax and find our voices again, perhaps even to laugh at our own reactions. But what if we can never relax? What if our early experiences shape our brain to be in a constant state of fear? This interference with the proper development and integration of neural networks can result in chronic stress and even mental illness.
What hard evidence do we have that supports this theory of language inhibition during stress? It turns out that the speechless terror often reported by victims of trauma appears to have a neurobiological substrate. In fact, a decrease in activation in Broca's area has been found in individuals with posttraumatic stress disorder during high states of arousal (Rauch et al., 1996). This inhibitory effect on Broca's area impairs not only language production but also the encoding of conscious memory for traumatic events. It may then interfere with the development of coherent narratives that serve to process the experience and lead to neural network integration and psychological healing. The dissociation we see in trauma survivors may well be an artifact of the loss of the cognitive flexibility provided by conscious awareness and language.
Another of evolution's decisions involves the vital importance it has placed on interpersonal experiences during the first years of life. These early memories, lost to our consciousness, nevertheless continue to shape our experience of those around us throughout our lives. To revisit our past learning in the present, where it is irrelevant or even destructive, is extremely problematic. The impact of these and other design compromises is certainly responsible for most of the difficulties people bring to psychotherapy.
The is an excerpt from Dr. Cozolino’s book The Neuroscience of Human Relationships.