Spotlight Series: Julianne McCall, PhD

The Science Behind Toxic Stress in Children

Julianne McCall, PhD, from the Governor’s Office of Planning and Research, discusses the science behind toxic stress in children and the importance of understanding the impact of early experiences on the developing brain.

I have a passion for neuroscience that was sparked by the neurological complications and developmental disabilities that have shaped my kid sister’s life. The complexity and uncertainty of her diagnosis launched me onto a career track to contribute to medical research that benefits patients in similar situations – for whom a diagnosis is persistently beyond reach, even when challenges are evident long before birth.

Today, I co-direct the California Initiative to Advance Precision Medicine alongside Dr. Shannon Muir, a Cancer Biologist. Housed in the Governor’s Office of Planning & Research, my role includes leading our new research program on Adverse Childhood Experiences (ACEs), an effort that will support ACEs Aware with new understandings of the physiological mechanisms of toxic stress, leading to more targeted strategies for prevention, diagnosis, and therapy for children and adults.

Studies have shown that early-life economic circumstances are predictive of various aspects of brain development, such as the volume of grey matter (consisting of nerve cells) in regions of the brain responsible for self-control, planning, and working memory. The greater the economic hardships, the less grey matter to work with. While our brains continue to change throughout adulthood in response to learning and new practices, this young field of science opened my eyes to the influence of one’s early environment on the fundamental architecture of our neural system.

To understand the impact of early experiences on the developing brain, keep in mind that neurodevelopment begins in utero. During the early years of one’s life, there are distinct windows of opportunity for brain development called “critical periods” when programmed biological growth depends on experiential factors, and vice versa.

Some critical periods begin to close within a baby’s first year. A seminal study of primates demonstrated, for example, that when one eye is deprived of light at birth through six months, normal vision can never develop, no matter how much sensory stimulation is provided afterward. What’s fascinating is that while the cells that compose the eye were technically functional, the brain structure responsible for facilitating vision was no longer active or capable of growing. Language acquisition is an example of a longer critical period. While adults, and better yet, teenagers, are perfectly able to learn a new language, the level of proficiency tends to be dwarfed by someone who learned a language before age 10, when fluency of a native speaker without an accent is achievable.

In a similar way, exposure to ACEs and trauma, without the social and emotional supports of a caregiver, also can leave an indelible imprint on the brain and body, which can then impact health in the short- and long-term.

The importance of screening and treating children and adults with ACEs and toxic stress cannot be overstated, especially when individuals and families are facing prolonged stress and uncertainties associated with the COVID-19 pandemic. For Black Americans and other communities of color, who are already at increased risk for toxic stress due to countless manifestations of systemic racism, the ACEs Aware initiative is integral to mitigating long-term effects.

Everyone routinely experiences stress. Some stress is positive, like the feeling a child may have anticipating the first day of school, or the stress an adult feels who is about to give a speech. Other stress is negative, like being in a car accident or losing a loved one. Negative stress can be tolerated with the right amount of social and emotional support. But prolonged or frequent stressors, like repeated exposure to domestic violence, can have profound impacts on a child’s development absent the protective buffers of a caregiver.

To understand the impacts, it helps to understand the stress response system. When someone experiences stress, the body automatically launches into some degree of fight-or-flight mode, activating what’s called the sympathetic nervous system. One’s rate increases, cortisol and adrenaline surge, digestion pauses, and energy increases, allowing the body to respond effectively in the moment. Once the stressful episode concludes, the parasympathetic nervous system kicks in to bring the body back to equilibrium. But if stress is sustained or frequently repeated during childhood, the body’s natural stress response system calibrates to an unhealthy level, more or less stuck on high alert.

While there are many avenues to mitigate the harmful effects of an overactive stress response system through a loving caregiver or wellness practices, without intervention, impacts can be measurable in the nervous, metabolic, immune, and endocrine systems that support basic functioning. Recent studies also have begun revealing how toxic stress can alter the intricate machinery of genetic regulation and maintenance, governing paths through which stress can be transmitted from one generation to another. This is the toxic stress response, and it can vary widely across individuals, for reasons that science has yet to fully grasp.

As the COVID-19 pandemic continues to disrupt employment, education, health care access, and family and community support systems, the incidence of ACEs and resulting toxic stress are likely to increase, putting individuals at greater risk for health problems at an unprecedented pace.

The California Initiative to Advance Precision Medicine aims to address this challenge in part with an equity framework by investing $9 million in research co-led by community health leaders and academic centers. Projects will apply an individualized approach to understanding the range of biological mechanisms of toxic stress from ACEs, from the genes you are born with to the environment and conditions in which you live, work, and play, known collectively as the Social Determinants of Health.

Our goal is to improve clinical approaches to preventing, diagnosing, and treating toxic stress and, ultimately, help reduce health disparities in underserved communities throughout California. Alongside ACEs Aware, this effort could not come at a more critical time in our state’s history. The health of our children, families, and communities depends on it.

Watch the video below to hear more from Julianne McCall.

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