Stress Effects Both Sides of the Brain

Aug 1, 2014

About this Article, “A Bihemispheric Autonomic Model for Traumatic Stress Effects on Health and Behavior”

This article by Sung Lee, Lee Gerdes, Catherine Tegeler, Hossam Shaltout, and Charles Tegeler (Frontiers in Psychology, 1 August 2014), is a contribution to a special research topic on the theme of Dysregulation of Autonomic Cardiac Control by Traumatic Stress and Anxiety. The topic brought together studies from numerous researchers who have shown how regulation of the heart rate can be disrupted by the experience of traumatic stress.

Background: Two main scientific findings inform the bihemispheric autonomic model (BHAM) presented. The first relates to division of labor between the left and right sides of the brain for management of the autonomic nervous system, the system that directs our level of arousal or mode of energy usage. The right side of the brain is the main manager of the “fight or flight” system, or sympathetic response, that releases energy stores, increases heart rate and blood pressure, produces sweating, steers blood away from the digestive system toward the large muscle groups, and primes our cognitive systems to lay down memories related to the context that is associated with this response.

The left side of the brain is the main manager of the “rest, digest, or freeze” system, or parasympathetic response, that produces effects related to lowering arousal, including digestion and uptake of energy, decreased heart rate, and behavioral stillness. The second scientific finding is polyvagal theory, which explains how the parasympathetic system has two different components that correspond to different stages of our evolutionary history. An ancient division produces low arousal for a “freeze” mode, with low resting heart rate, and is active when we orient to a new stimulus or if we are overwhelmed by a stress (or series of stresses). An evolutionarily more modern division produces low arousal that indicates an authentic state of calm, with variability in the heart rate that reflects dynamic flexibility.

Main ideas of the model: The BHAM integrates appreciation that the right and left sides of the brain are the main managers for the sympathetic and parasympathetic divisions, respectively, with the polyvagal theory. The BHAM states that when a person is in a relatively healthy state without excess stress or trauma, the regions of the left and right sides of the brain that are responsible for managing the autonomic nervous system, will fluctuate naturally in association with changing arousal levels, according to the natural rhythms of life – a balance between self-calming and excitement. If a person has an acute stress that is associated with a heightened expression of high arousal (fight or flight), then they may become at risk for right-side dominant activity in the region of the brain responsible for autonomic (sympathetic) management. If they have repeated stresses or a single severe stress, they may become at risk for left-side dominant activity in the region of the brain responsible for autonomic (parasympathetic) management. In cases of either right or left side dominance, individuals may also come to be at increased risk for maladaptive compensatory behaviors, that represent the brain’s attempt to become “unstuck.” For example, right-sided “stuckness” in high-arousal might produce a particular risk for abuse of alcohol or other sedating substances. Left-sided “stuckness” in low-arousal might produce a risk for behaviors (rage, stimulant abuse, anti-sociality) that help a person come out of a state of numbness. The BHAM is illustrated with case studies showing the role of technology that supports the brain to balance its left and right sides, to support recovery from the effects of accumulated stress.

Authors’ conclusion: The authors conclude that, given the high prevalence of stressors in the modern world, the BHAM and related interventions have an important role to support advanced understanding and practice for optimizing functionality of the human stress response system.

Read full article here.

*More information about the HIRREM Research Program at Wake Forest School of Medicine, PI Professor Charles Tegeler, M.D., is available at  The Program has received nearly $3.5 million in independent funding since 2011, from the Susanne Marcus Collins Foundation, Inc., the United States Office of the Secretary of Defense through a contract with US Special Operations Command (USSOCOM), the United States Army Research Office, and others.

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