The Physiology of Fear

Recently, I wrote a piece about maladaptive fear and someone asked me to explain the physiology of it. Although I am certainly not an expert, and no one fully understands the physiology of fear, I shall endeavor to do my best to explain it in detail.

Please, forgive me if I get something wrong and read all the way to the end to find the answer to the question, “Why do I feel afraid all the time?”

The Central Nervous System


 To understand fear we must first explore some brain anatomy.

There is a tiny almond-shaped duo region in the brain called the amygdala that is part of the limbic system located deep inside the temporal lobe. The amygdala is responsible for recognizing and remembering (via the hippocampus) danger and when it sees a stimulus that is perceived as dangerous secretes stress hormones that activate the hypothalamus.

The hypothalamus, in turn, secretes the stress hormone epinephrine (aka adrenaline) that then activates the pituitary gland located on top of the kidneys. The pituitary gland secretes another stress hormone known as adrenocorticotropic (ACTH) that circulates throughout the body revving up the body for the fight/flight/freeze response. The heart will beat faster, blood pressure will rise, the eyes become dilated, and all parts of the body considered unnecessary at the moment are shut off from blood supply as the blood is pumped into the extremities so we can run away.

All these chemical reactions and happen in a split second and the reactions to perceived dangerous stimuli are not consciously controlled by the person experiencing the fear.

The Results of Childhood Trauma on the Physiology of the Brain and Mind


There is a myriad of different negative effects that childhood trauma has on brain development including the following:

  • Behavioral problems
  • Memory problems
  • Focus issues that cause learning difficulties
  • Negative effect on the ability to control oneself
  • Poor prioritizing and planning skills
  • Lack of resilience
  • Issues with social skills

There are many psychological issues related to trauma on the brain including but limited to the following:

  • Anxiety Disorders
  • Depression
  • Adult ADHD
  • Dissociative Disorders
  • Low Self-Esteem
  • Impulsivity
  • PTSD
  • Complex PTSD
  • Borderline Personality Disorder
  • Stress Disorders
  • Substance Abuse

Not only are we affected in mind and body but our life spans have also been lessened by the flood of stress hormones that flooded and still flood our bodies every day from the childhood trauma we faced by up to 20%.


Flashbacks, Anxiety, and the Amygdala

Childhood trauma of any type causes the amygdala to perceive fear even when the threat is over. This is because this small brain region remembers the sight, sound, smell, and tactile feelings that came along with the original trauma.

When the child becomes an adult, the amygdala keeps signaling danger and feels and responds to a trigger that reminds it of the events of the past.

For instance, a traumatic event, experienced in childhood, was accompanied by a song playing on the radio during the episode. In adulthood, when the person hears that song fear is triggered and we might experience a flashback accompanied by a panic reaction. This reaction occurs thanks to the amygdala that remembers the sound of the song playing on the radio and does not perceive the danger as passed but as though it were happening in the present.

The stress hormones released into the human body as a response to repeated trauma forever changes brain structures such as the amygdala and the hippocampus. In essence, we who have experienced severe childhood trauma have a form of brain damage.

This brain damage is evident in MRI studies conducted on people who are diagnosed with post-traumatic stress disorder. The MRI studies show that the amygdalae and hippocampi of adults who were traumatized as adults are smaller than normal because of the stress hormones that flooded their young developing brains in childhood. This means that their brains were less able to perceive something as not dangerous after the fear response has been triggered causing the body and brain to go into overdrive every time danger is perceived.

MRI Studies and Dissociative Identity Disorder


The validity of dissociative identity disorder (DID) has long been debated in the scientific and psychological world. However, in 2006 Vermetten, et. al conducted a series of MRIs on people diagnosed with DID and what they found is staggering.

The volume of the hippocampi in the subjects who had DID was 19.2% smaller and the amygdalar volume was smaller by 31.6% than control subjects. In fact, compared to the control group, the research showed a remarkable and significant difference between the brains of the two sets of subjects.

These changes to the brains of people living with dissociative identity disorder were caused by early stress associated with changes in the structure of the hippocampus and amygdala. The amygdala is hyperactive making one feel afraid all the time and the hippocampus remembers the trauma and will not allow the body’s stress hormones to return to baseline.

This inability for our bodies to return to baseline, where the stress hormones recede and we become calm, is why we experience life awash in fear and fear responses.

Desensitizing the Brain

There are a few ways to help the fear response lessen. One is to practice mindfulness when you practice staying in the now. I’ve attached a link to help you find my piece on how mindfulness helps calm the storm caused by childhood trauma in adulthood.

Another help is to work with a therapist to desensitize your amygdala by working through the traumatic events that happened so long ago and laying aside the triggers.

Finally, learning grounding techniques can help you respond better when a trigger does occur. After learning and practicing grounding, you will recognize the trigger faster and bring yourself back into the present more quickly than before.

I hope this piece helped explain some of the questions that might be floating around in your brain as you wonder about why you are afraid all the time. You are not weird, nor are you defective. Your brain has learned to experience fear in the present through triggers and that was absolutely not your fault, nor should you be ashamed because of it.

My final word to you is this. You are now in charge of your life and how you respond to it. Yes, the childhood trauma in your past affects you in many different ways, but you and only you can change that. There are no magic pills, nor is there a therapist who knows it all and will cure you. The ball is now in your park and it is up to you to pick up the bat and send the past into the past where it belongs.

My Book


The following statement isn’t a shameless plug because I truly believe much of the information you are looking for is found here.

If you would like to read more (this information is the tip of the iceberg) I encourage you to purchase a copy of my book The Last Comprehensive Resource Book About Dissociative Identity Disorder You Will Ever Need.

 The book is available in paperback and right now it is available to Kindle Unlimited for free.

“When we let go and stop dragging the pain and past, we free ourselves of dead weight and allow our hearts to heft the good stuff…the stuff that makes our journey lighter, easier, and more meaningful.” ~ Toni Sorenson


De Bellis, M. D., & Zisk, A. (2014). The biological effects of childhood trauma. Child and Adolescent Psychiatric Clinics, 23(2), 185-222. DOI: 10.1016/j.chc.2014.01.002

Davis, S., (2020). Mindfulness for healing from complex traumatic-stress disorder. WordPress.

Grupe, D. W., & Heller, A. S. (2016). Brain imaging alterations in posttraumatic stress disorder. Psychiatric Annals46(9), 519-526.

Hosier, D., (2017). How Childhood Trauma Can Disrupt Developmental Progress. publications, 1 ed. Retrieved from:

Keifer Jr, O. P., Hurt, R. C., Ressler, K. J., & Marvar, P. J. (2015). The physiology of fear: reconceptualizing the role of the central amygdala in fear learning. Physiology, 30(5), 389-401.

Mora, F., Segovia, G., del Arco, A., de Blas, M., & Garrido, P. (2012). Stress, neurotransmitters, corticosterone and body–brain integration. Brain research1476, 71-85.

Teicher, M. H. (2000). Wounds that time won’t heal: The neurobiology of child abuse. Cerebrum2(4), 50-67.

Vermetten, E., Schmahl, C., Lindner, S., Loewenstein, R. J., & Bremner, J. D. (2006). Hippocampal and amygdalar volumes in dissociative identity disorder. American Journal of Psychiatry, 163(4), 630-636.















2 thoughts on “The Physiology of Fear

  1. Dearest Shirley,
    I read your recent post on DID. I left me with much more understanding of the disorder that I suffer from. Infact, it gave me so much hope I began to cry. The tears that were shed, came from deep inside most likely from Kimmie my smallest self. To know that there is hope out there makes today much easier to live through, Thank you!


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