The Physiology of Trauma

Baby's foot cupped within parents's hands

Credit: Let Grow Therapy and Counseling - Helping Children to Thrive. Creative Commons License 2.0

Trauma and Post-Traumatic Stress Disorder

Post-Traumatic Stress Disorder (PTSD) is a prominent mental health issue that affects millions of individuals worldwide. In the United States, an estimated eight percent of the population will experience PTSD at some point in their lifetimes. PTSD is caused by trauma, and while it is most commonly associated with negative psychological effects and symptoms, the disorder has a large physiological component as well that is a crucial focal point in the treatment process. All individuals who have experienced trauma are susceptible to experiencing a variety of negative effects and symptoms, especially if they do not receive appropriate support and treatment following the traumatic experience(s). It is widely known that unresolved trauma negatively affects individuals who experience it, however, recent research has found that trauma and some of its effects can be genetically passed down to future generations. However, the “transgenerational epigenetic inheritance” of trauma, as this would be known by scientists, is not accepted by a majority of behavioral geneticists, although it has been widely touted as settled fact by the mainstream press.

When is an Event Considered Traumatic

Trauma and Post-Traumatic Stress Disorder (PTSD) are commonly associated with the military and individuals who have experienced combat and other aspects of war, however, there are many other events and experiences that can also be traumatic and that can lead to PTSD. An event is considered “traumatic” when individuals perceive and experience a threat to their life or physical safety or sense of stability of the world around them. Given this definition, it makes sense that a large percentage of individuals affiliated with the military experience PTSD. Other events and experiences that are associated with trauma and high risk of leading to PTSD include rape and other forms of sexual assault, natural disasters, abuse, motor vehicle or other accidents, witnessing death or torture, and many other situations where a person’s well being is severely threatened, leading to an intense stress response that overwhelms the nervous system. While there are a number of events more commonly associated with trauma and PTSD, trauma is subjective, so while one individual may experience a specific event as traumatic and may experience symptoms of PTSD as a result, another individual who experienced the same or similar event may not experience it as traumatic. It is important to recognize that it is not the facts or details of the event that make it traumatic but the way it was perceived and experienced by the individual.

Physiological Effects of Trauma

Trauma occurs when the nervous system becomes so overwhelmed that the brain is unable to process what is happening. Because the brain is unable to process what is occurring, the information cannot be properly integrated, resulting in the inability to restore equilibrium. As threat, shock, and fear are perceived and experienced, energy and arousal levels sky rocket to an overwhelming and unmanageable level, and this energy gets locked and stuck in the body’s nervous system. When this energy and arousal is not released, it causes a number of physical and emotional symptoms. Trauma and traumatic stress can alter brain structure, causing lasting changes in the hippocampus, prefrontal cortex, and the amygdala as these three areas are highly involved in the physiological response to stress. During a traumatic experience, the neurotransmitter, norepinephrine, highly associated with the body’s stress response, becomes increased to an abnormal level, and the amount of the hormone, Cortisol, that controls the level of norepinephrine, becomes decreased. In individuals who have experienced trauma or are suffering from PTSD, norepinephrine levels become elevated in stressful situations following the initial traumatic experience, and these abnormal levels play a large role in PTSD symptoms.

Trauma and Genetics

While providing appropriate support and treatment to trauma survivors is important for obvious reasons regarding their personal safety and well-being, recent studies on the topic has uncovered a potential additional layer to the detrimental effects of trauma that makes healing and treatment for those who have experienced it even more crucial. Research has found strong evidence for epigenetic inheritance, a theory stating that one’s experiences and environmental influences can genetically affect one’s offspring and future generations. In studies of trauma survivors and genetic analysis, it has been shown that children of those who have experienced trauma or PTSD are more susceptible to developing mental health issues and disorders relating to stress. This information demonstrates trauma’s ripple effect as these experiences may have affected current generations and will continue to have a negative impact on future generations, leading to an increase in mental health issues. These findings continue to stress the importance of mental health support and treatment for those who have experienced trauma as unresolved and lingering trauma can have serious effects on the individual and potentially on their children and generations to come.

Nature vs Nurture: Parental PTSD Directly Impacts Children's Emotional Health

The hypothesis that trauma can be directly passed on to succeeding generations genetically is controversial and is by no means settled science. However, there are well-established mechanisms for the intergenerational transmission of trauma that can be simply explained by the children's reaction to their parent's symptoms. This underscores the importance of support and treatment of PTSD sufferers to minimize the impact on future generations.


American Psychiatric Association. (2013). Diagnostic and statistical manual of mental disorders (5th ed.). Arlington, VA: American Psychiatric Publishing. Text citation: (American Psychiatric Association, 2013)

Bremner, J. D. (2006). Traumatic stress: effects on the brain. Dialogues in Clinical Neuroscience, 8(4), 445–461.

Levine, P. A. (2010). Resolving Trauma in Psychotherapy: A Somatic Approach. Mill Valley, CA:

RAINN. (2016). Post-Traumatic Stress Disorder.

Thomson, H. (2015). Study of Holocaust survivors finds trauma passed on to children's genes. The Guardian.

Birney, Ewan (2015) Why I'm sceptical about the idea of genetically inherited trauma. The Guardian

US Department of Veteran Affairs. (2016). How Common is PTSD? In PTSD: National Center for PTSD.