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  • Sattvik Basarkod

Overview of Critical Periods Study

Updated: Jul 5, 2023


Urban childhood trauma presents a significant crisis in Detroit, and around other major metropolitan cities. The Critical Periods Study aims to understand how trauma affects brain development and body response to fear stimuli. Trauma, whether physical or mental in nature, often involves changes in our moods, behaviors, and overall personality. Trauma exposure in childhood is even more detrimental to long-term mental health and brain development. Regardless of what gender, race, or ethnicity we identify as, we all face trauma, but there are several factors that influence our healthy response and resilience. One of those factors is how we learn to be afraid: fear acquisition and extinction.

Fear acquisition is the ability to learn danger and remember threatening things around us to help us stay safe. Fear extinction is the ability to learn that a particular past bad event is no longer threatening. Together, fear acquisition and extinction allow us to stay safe and recover from traumatic events. We can’t often change the external situations in our childhood. Children are dependent on their parents and their surroundings; and they usually cannot escape their situation. Thus, their bodies learn fear in a way that best fits their environment. Our lab’s goal is to study the physiology of fear acquisition and extinction, and to link it with children’s trauma exposure and PTSD ratings. PTSD, or post-traumatic stress disorder, is a psychiatric condition where the individual suffers from unwanted memories, hyperarousal (overreaction to trauma reminders), alterations in mood, and avoidance (isolation). Although physical and sexual abuse are strong contributors to PTSD, other mental stressors can also increase risk for PTSD. There are two types of stressors: direct and indirect. Direct stressors involve the person being the subject of the trauma, while indirect stressors involve the person seeing someone in their family, or a friend or neighbor experience trauma. Indirect stressors such as witnessing frequent neighborhood fights, school violence, and home arguments can drastically change the way a child’s response to fear develops. Our study aims to better understand the risks for PTSD and its implications on fear circuitry.

Picture credits to Hiawatha Valley

General trauma is present in most of us because it reflects our sympathetic nervous system, also known as the fight or flight system developed for evolutionary purposes. The fight of flight system allows the brain to quickly act in danger without having to employ much decision making or higher-level thinking. Neuroanatomically, our brain areas can be thought of as organized along two pathways: “the high road” and “the low road”. The high road takes time and involves our higher areas of the brain that control decision making and rational thinking. On the other hand, the low road is fast and involves our emotional centers that work on impulse and immediacy. When our bodies see something threatening and initiate the fight or flight response, our low road is activated, and in turn our emotions are heightened and our ability to think is suppressed. It is on this premise that we believe that frequent trauma exposure leads to an impaired fear response in the brain, and further increases children’s chances for PTSD. Some of the signs of the fight or flight response include elevated blood pressure, increased heart rate, heightened skin conductance (sweat), increased reflexes (eye blink), and pupil dilation. The fear-potentiated startle paradigm measures the activity of our sympathetic nervous system and allows us to determine how it associates with previous trauma exposure.

Aims and Hypotheses of the Study

Aim 1: Study how fear-potentiated startle (fear acquisition and extinction) associates with trauma exposure.

Hypothesis 1: We hypothesize that trauma exposure prior to age 9 will increase fear-potentiated startle to conditioned danger signals and decrease discrimination between danger and safety signals.

The fear-potentiated startle test measures someone’s fear response. In our lab, we measure heart rate, skin conductance, and eye blink muscle activity. We hypothesize that children who have experienced a traumatic event before they were 9 years old will have an increase in these measures. Additionally, the children with trauma will also have difficulty distinguishing danger and safety signals due to impaired physiological responses to safety.

Aim 2: Study how neurocircuitry is impacted by trauma exposure in children and adolescents.

Hypothesis: We hypothesize that trauma exposure will be predictive of alterations in the limbic structures and decreased prefrontal cortex activation and decreased structural and functional connectivity of amygdala and prefrontal inhibitory areas.

This hypothesis is based on the “high road” vs “low road” of our brain’s response to danger. The limbic parts of the brain represent the “low road” and are involved in fear learning, according to previous research in animal and human models. We hypothesize that there will be changes in the limbic structures based on trauma exposure. Usually, the limbic structures are regulated by our higher areas of the brain, mainly the prefrontal cortex, representing the “high road”. However, repeated trauma exposures can reduce the activity of prefrontal cortex and its connection to the amygdala. Because of the reduced regulation of amygdala, the fear response is exaggerated and becomes pathological in brain development. This entire process can be measured using brain scans.

Aim 3: Identifying how trauma exposure is related to critical periods in development of children.

Hypothesis: We predict that the impact of trauma exposure will change with age, in that high levels of trauma will alter brain development trajectories. We also predict trauma exposure after 10 years of age will result in a different developmental pattern compared to those with trauma exposure prior to age 10.

Here, our lab is hypothesizing that trauma exposure that happens during certain times during development might have a different impact compared to other times. We believe that children with trauma before the age of 9 will have different developmental pattern than children with trauma after 10 years. The age range between 9-10 is just one of the critical periods theorized to be important in the development of the brain.

Study Overview

The Critical Periods Study is a longitudinal study that examines the effect of trauma on brain development. We start by recruiting families with children that are 9 years of age, and who may have experienced trauma before. These families are then contacted over the period of 2 years for longitudinal visits. Each visit contains two parts: the startle and interview and the brain imaging visit. The startle and interview last for 4 hours, and contains the fear-potentiated startle test and a set of interview questions to measure trauma exposure. The brain imaging visit (we use an imaging method called magnetic resonance imaging, or MRI) lasts for 3 hours and contains 3 tasks/ games that are used to measure the child’s structural and functional brain connectivity. Currently as of August 2022, we have longitudinal data from around 45 families, and at least one visit data from around 75 families.

Some Findings

As this study is just finishing, we are still working on data processing and analysis. Some of the scientific papers that are written from this study include: 1. Intolerance to uncertainty and its impact on PTSD severity; 2. Association between childhood trauma and skin conductance. They are attached below, and I have summarized their basic findings as well.

Findings from Intolerance to uncertainty and its impact on PTSD severity:

Our lab was interested in studying the relationship between children’s ability to realize when a danger signal stops predicting something bad and becomes safe, and their physiological response to the initial danger sign. We found out that children who were more aware of the change in danger/ threat or who took less time to discover the changing pattern were also the children who had fewer hyperarousal signs and less PTSD symptoms. The main finding of this paper was that cognitive flexibility towards unlearning danger and learning safety is associated with reduced PTSD symptoms. This suggests that PTSD treatments can be more effective if they are linked with flexible thinking patterns. Cognitive flexibility can be a strong factor in resilience and decreasing physiological hyperarousal response to potential danger signs.

Findings from Association between childhood trauma and skin conductance:

Figure 1: The graphic up top shows how we collected data on skin conductance. Children were asked questions about their past traumatic events while we recorded their SCR. Esense is a very feasible method of collecting SCR data while doing trauma interviews. Our studies show children with high trauma also have higher SCR.

Our lab found that children who reported more traumatic events during an interview had a higher skin conductance response while talking about trauma. Skin conductance increases when we sweat more. Our sweat contains salts, which naturally increase the electric conductance, and allows us to measure electrical signals from the body more easily. Figure 1 above demonstrates how we used skin conductance equipment (Esense) to collect SCR while also administering trauma measures. Increased skin conductance during trauma interviews suggests that we can start to use technology to derive more objective measures of trauma response and determine risk for PTSD. The underlying principle behind using psychophysiology data such as skin conductance is to find biomarkers that predict vulnerability to PTSD.

Factors of Improvement

Picture Credits: Rebekah Ballagh

Figure 2: Our freeze, flight and fight responses can fluctuate throughout our life, but being mindful and aware of the present moment can allow us to calm ourselves and be more positive.

Although our research is more designed towards understanding ways that changes in the brain and body might lead to PTSD rather than treatment of the disorder, these measures will be able to assist us in developing better treatments in the future. Some key factors that improve mental health following a traumatic event can be found in our research. As mentioned earlier, there are both physical and mental stressors so one of the most important things is to be aware of our environment and our arousal in response. Children who are more aware of their stressors tend to have better coping skills and develop resiliency. This is well aligned with the mindfulness movement, which asks us to be aware of not only our surroundings, but also our own inner selves. Mindfulness strengthens the part of the brain that regulates our emotions and therefore allows us to make better decisions without becoming overwhelmed in a stressful moment. Other ways of improving resiliency include movement exercises such as dance, yoga, and sports as well as art activities such as painting, drawing, and coloring. These help children to invoke their creativity and become less caught up in their past experiences. In general, being in the present moment by doing these various activities allows children to let go of their past and move towards a better future.

We would like to acknowledge and thank all our Critical Periods families and kiddos that contributed to our research! This research wouldn't have been possible without them.

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2 commentaires

Tara Clark
Tara Clark
20 déc. 2022

Thank you


19 déc. 2022

Thank you all

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