Bruce Perry, M.D., Ph.D.

Neuroscience of Trauma and its Impact on Development

Through a process called patterning, our brains acquire and accumulate knowledge from the external world. Patterning is the brain’s way of categorizing and organizing information. The brain perceives patterns and generates patterns then uses those patterns to predict appropriate responses to future stimuli (Willis, 59).  Thus, when Pavlov began his research on the conditioned response, which observed that an individual’s mouth will salivate at the sound of a bell if the brain had been conditioned to associate the bell with the reward of food, what was being observed was the brain’s patterned response to series of stimuli. If the brain perceived a disruption in the pattern, i.e. if the bell was no longer partnered with food, then the brain would extinguish the pattern of the conditioned response (van der Kolk, 2014). The brain’s patterning process allows the brain to develop complex webs of historical information that it is constantly recruiting in order to process incoming information. During the early stages of life, when the brain experiences 90% of its growth, the parent-child relationship is the primary source of information for the child; this relationship has an acute and lasting effect upon the child’s development (Perry, 2017).

The complex webs of historical information are referred to as neural networks. The efficacy of these neural networks depends upon the organization of their development. Their primary function is to transmit information from one area of the brain to another and to identify, categorize and catalogue stimuli. Thus, individuals experiencing predicable, controlled and moderate stimulus will develop efficient and organized networks that will transmit information in an organized manner creating an appropriate response to external stimuli. However, those individuals that experience uncontrollable, unpredictable and varying intensity of stimuli will develop neural networks that are inefficient and disorganized in their response to external stimuli. Children who experience maltreatment at pivotal stages of development are the recipient of unpredictable, uncontrolled stimuli that varies in intensity. This disruption to the brain’s typical development produces neural networks that respond to external stimuli in a disorganized way, this disorganization manifests as maladaptive behaviors, e.g. the inability to recognize actual and perceived threat.

“By conservative estimates, about 40 percent of American children will have at least one potentially traumatizing experience by age eighteen: this includes the death of a parent or sibling, ongoing physical abuse and/or neglect, sexual abuse, or the experience of serious accident, natural disaster, or domestic violence or other violent crime.”

The Boy Who Was Raised as a Dog: And Other Stories from a Child Psychiatrist’s Notebook

The brain has three responses to threat; fight, flight, or freeze. The brain can recruit these responses as needed and will often respond to threat with a combination of these. They are best described as existing on a spectrum; at one end is the fight/flight response, or arousal, and at the other end is the freeze response, or dissociation. The traumatized child that cannot discern actual threat cannot regulate the spectrum. Some children may remain in hyperarousal, some may dissociate, and others may remain in a holding pattern, cycling between both. While the child remains in this holding pattern, their brain is saturated with stress hormones such as epinephrine, cortisol, opioid peptides, serotonin and dopamine (Perry, 2013).

Hyperarousal threat responses are characterized by the well-known fight or flight response. Here, the body is prepared to fight the trauma, or the abuser. Hyperarousal also prepares the individual to flee the threat. The hyperarousal state is most often experienced by the older child, adolescent, or adult. At these stages of life, most people are capable of fighting or fleeing; however, when the trauma is immobilizing and inescapable, when there is no way out, and no way to fight, the individual will sometimes dissociate. Dissociation is most commonly experienced by infants to elementary age children, and primarily by females. Dissociation is characterized by disengagement, depersonalization and derealization; all states of consciousness in which the child’s brain mutes external stimuli, creating a sensation of separation of mind and body, child from trauma. It is important to recognize that the brain does not use one of these responses exclusively and in fact will use them in combination as a response to trauma (Perry, 2013; van der Kolk, 2005).

Educators intuitively understand that children in a calm state of reflection learn best; what may not be understood about this state is the neurobiological implications. The human brain is a processor that engages a multi-layered operating system. These operating systems are the brainstem, diencephalon, limbic and neo-cortex (see Figure 1). Each of these operating systems process external stimuli differently, while equally contributing to our body’s response to stimuli. In a typically developed brain, most of these operating systems operate nearly simultaneously. The most basic, primitive, operating system is the brainstem; it operates reflexively, enabling it to orchestrate split second decisions. The diencephalon, the second brain layer, is characterized as the emotionally reactive region; the limbic region increases in complexity but produces concrete thought, sometimes described as a black and white perspective. The neo-cortex region, our most complex operating system, is characterized by a state of reflective thinking. The neo-cortex region is where our brain processes language, philosophy and abstract thinking, such as algebra; it is activated when the child is in a state of calm. Calmness allows the brain to recruit each of its operating systems to produce appropriate responses to external stimuli (Perry, 2013).

“Surprisingly, it is often when wandering through the emotional carnage left by the worst of humankind that we find the best of humanity as well.”

The Boy Who Was Raised as a Dog: And Other Stories from a Child Psychiatrist’s Notebook

The child that is constantly traveling the threat response spectrum spends most of their brainpower operating the brainstem and limbic regions. Incapable of discerning the difference between actual and perceived threat, the child’s brain is constantly on alert and activating neural networks that are sending information to the brainstem, in preparation for the coming trauma. The child’s brain is incapable of transferring control from the brainstem to the higher, complex, thinking regions of the limbic and neocortex; this prevents the child from absorbing and processing knowledge, leading to academic and cognitive delays (Perry, 2014). The traumatized child in the classroom may seem exasperatingly fidgety, sensitive to the slightest noise and their eyes may seem incapable of meeting the teacher’s, in what appears to be obstinance, but is really the brain training the eye to look for threat.

The traumatized child is excessively recruiting the limbic and brainstem areas of the brain leading to a saturation of threat response hormones. This saturation of hormones results in imbalanced development of regions of the brain, specifically the amygdala and the hippocampus. The amygdala acts as a flagger and is responsible for flagging external stimuli as a threat (van der Kolk, 2014). If the amygdala is the flagger, the thalamus is the directional. It absorbs stimuli and sends it on the high road, i.e. to the neo-cortex region, or down the low road, to the amygdala (van der Kolk, 2014; Willis, 2010). The thalamus and amygdala operate as a checks-and-balance system within the brain and when this system breaks down, traumatized children experience an imbalance in this process, resulting in the over production of stress hormones.

Nestled next to the amygdala is the hippocampus. The hippocampus is responsible for encoding memory into patterned highways of information, otherwise known as neural networks. In this process the hippocampus recruits stored knowledge and binds it to incoming stimuli to produce neural pathways (Willis, 2010). Continual activation of the amygdala region prevents sustained attention and leads to deactivation of the hippocampus (Fotenbaugh et al., 2017). In order for educators to effectively teach traumatized children it is important for them to have an understanding of the physiological challenges created by trauma. By understanding the obstacles that children face, educators will be better equipped to develop individualized educational pathways for these children. 

An introduction to Dr. Bruce Perry and his research…

This is a video that provides an introduction to the work and research of Dr. Perry. It is a longer video but it covers quite a lot of material from his research. It can be viewed as a guide through his research and how it has molded his therapeutic approaches.

Neurosequential Model Therapy (NMT), Empathy and ChildTrauma Academy…

Founder of the non-profit, ChildTrauma Academy and co-author of the book, The Boy Who Was Raised as a Dog: And Other Stories from a Child Psychiatrist’s Notebook, Dr. Perry has spent forty-plus years researching and observing the effects of trauma on development. From his research and observations, he has developed a therapy model that he has labeled Neurosequential Model (NMT). NMT is not an intervention, and does not follow a specific therapy protocol, instead it is a way to inquire and categorize the strengths and deficits of children affected by trauma. Perry describes this process as a “developmentally-informed, biologically-respectful approach” (, that helps Perry identify specific interventions and treatments that can be used assist in the healing process of these individuals.

NMT is founded on the neurological research that Dr. Perry conducted over forty years. Below are several videos that describe the neurological effects of developmental trauma. These videos can be found at .

The first video describes how the human brain develops and why this is important to understanding the neurological response to trauma.

This second video describes the impact of prolonged and complex trauma on the brain’s development.

The third video describes how traumatized children respond to threat and how that response creates patterns for future reactions.

This final video describes how learning and development is impacted by the state in which we are operating.