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The Trauma Experience: Our Brain in Three Parts: Reptilian, Mammalian, and Neocortex

Updated: Jan 20

DR. ESSLIN TERRIGHENA explains how our triune brain encodes trauma and contributes to trauma responses even years after our traumatic experience.

Understanding the triune nature of our brain can shed light on how traumatic events are encoded, processed, and may later trigger trauma responses even long after the initial event took place. Dr. Bernie Siegel introduced the concept of the triune brain in which our brain is understood as the interaction of three parts: the reptilian brain, the mammal brain, and the human brain.

The reptilian brain

This part of our brain is located at the base of the skull and includes the brain stem, cerebellum, and basal ganglia. It handles functions that are outside of our conscious control, including breathing, heartrate, digestion, reflexes, and other physiological processes. It is key to our survival responses involving fight-flight modes, feeding habits, and reproduction. This is our oldest brain structure and contributes to keeping us alive.

The mammalian brain (limbic system)

This part of our brain is in the mid-region and includes the amygdala, thalamus, hypothalamus and hippocampus. It is particularly relevant to our experience of emotions, emotion processing, sympathetic and parasympathetic nervous system activation, and memory. This is the said to be the second oldest brain structure and particularly pronounced in mammals.

The Neocortex brain

This part of our brain is located in the upper regions of our brain and is responsible for executive functioning, critical thinking, analysis, communication, conscious decision-making, planning, logic, and emotion regulation.

During a traumatic experience, there are high levels of brain activity in our reptilian and mammal brain areas – intense emotions and survival responses. Together, they warn us of danger and activate physiological and behavioural processes that aid our survival, including fight, flight, freeze and fawn. The cortical brain has less activity in this time due to the allocation of processing resources to the mammal and reptilian brain parts. Thus, it is harder for us to make rational, analytical decisions.


Post-Traumatic Stress responses

Due to the involvement of memory formation in the mammal brain and the dulling of the cortical brain during trauma, our brains may form a particularly intense emotional reaction to triggers associated to the traumatic incident. For example, after a car accident, we may suddenly become fearful of cars, horns, streets signs, or certain streets. When confronted with any of these triggers, we may have a sudden surge of activity in our reptilian and mammal brains, and experience the same internal state as during the actual accident, even though in reality we are safe and sound. This is what we refer to as a post-traumatic stress response.

What can help?

It can be difficult to try to engage the cortical areas of the brain engaged when there is so much activity in mammal and reptilian areas – the experience can feel altogether overwhelming. Trauma therapy is beneficial in starting to re-wire the brain, reducing the intensity of the post-traumatic stress response and creating meaning from the traumatic event that promotes healing and growth. There are other measures you can also take in the present to help soothe and calm the body, activate cortical areas, and avoid being fully pulled into a trauma reaction:

  • Grounding – this is about getting yourself out of your head and into your body. It can be important to keep your eyes open (rather than closing them) during a post-traumatic stress response to give your brain a better chance to recognize where you are and make a more appropriate safety analysis based on what is around you. Small steps to engaging your cortical areas include naming things in your environment that are a certain colour, looking for shiny objects, and describing the scene out loud using all five senses. Touch can also be powerful here, for example pushing your hands into a sturdy wall or ground can help the body to feel more connected and safer in the here-and-now. To try a 6-min grounding exercise called the Butterfly Hug, please click here.

  • Breathing – 4-4-8 breathing in which you breathe in to the count of four, hold for the count of four, and breathe out for the count of eight can help to activate the parasympathetic rest-and-recovery system, which counteracts our survival mode (fight, flight, freeze, fawn). It is important here that the exhale is twice as long as the inhale. This signals to the body that things are safe and calm. Keep this breathing cycle going for 3 to 5 minutes. For a guided 448 breathing exercise, please click here.

  • Questions – if you have some access to the cortical areas, try to ask yourself questions about your experience. For example, does this emotional reaction belong in the now or in the past? What is safe around me? What do I need right now? What part of my brain am I in right now? These questions can increasingly engage the cortical areas, allowing them to make a more accurate assessment of our surroundings and reality.

If you are experiencing symptoms of post-traumatic stress and want to find out how trauma therapy can help you, please book a consultation with psychologist Dr. Esslin Terrighena, please contact (852) 2521 4668 or

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