Brain Development and Toxic Stress
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The document discusses how brain development is most rapid from birth to age 5, as the brain triples in mass and growth involves forming new connections. Certain areas of the brain, such as those involved in emotions and stress response, are particularly sensitive during this period. Experiences with strong, frequent, or prolonged stress without support from caring adults can lead to "toxic stress", damaging the prefrontal cortex and increasing fear and anxiety even in safe situations later in life. This is due to the stress response becoming conditioned to generalize fear more broadly. Removing the danger later does not necessarily "fix" the effects of early childhood toxic stress on brain development and behavior.
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Brain Development and Toxic Stress
- 1. Brain Development and Toxic Stress Jordan Greenbaum, MD Stephanie V. Blank Center for Safe and Healthy Children Children’s Healthcare of Atlanta 1
- 2. Basics of Brain Development • Most neurons present at birth • From birth to 5 years, brain triples in mass • Growth involves connections
- 3. Brain Maturation Location is everything!
- 4. 4 Sensitive Periods • Windows of opportunity – Effects of experience on brain are very strong – Vary with area of brain – Initial experience is more influential • Plasticity persists (it’s never too late!)
- 5. Neural Plasticity • Continues to a certain extent throughout life • Decreases with age • Allows us to compensate for injuries, change behavior, learn
- 6. 6 Some Critical Areas of the Brain • Emotions and stress response • Contextual memory • Executive functions • Interact with each other Prefrontal cortex
- 7. Let’s Talk About Stress!!
- 8. 8 Hot Spots for the Human Stress Response prefrontal cortex cingulate gyrus
- 10. 10 Hypothalamic-Pituitary-Adrenal Axis • Initiated by amygdala • Cortisol secreted within minutes • Effects seen for hours
- 11. So, how does this work?
- 13. 13 Toxic Stress • Toxic stress: – Strong, frequent or prolonged – Often uncontrollable – No supportive adult
- 14. • Particularly malleable during fetal and early childhood periods • Experience influences later responses to stress • Fear conditioning – Neutral stimulus associated with aversive one that causes fear – Gradually neutral stimulus comes to elicit fear – Can generalize further to other neutral stimuli • Stress Response
- 15. • Increases fear, stress, anxiety in ‘safe’ situations • Impacts social interaction, behavior, learning • Prefrontal cortex damage is key • Can occur even in infants • Removing the danger doesn’t ‘fix’ the child Generalized Fear-Conditioning
- 16. 16 Prefrontal Cortex Amygdala Hippocampus Brainstem Arousal, Focusing FFFPrefrontal Cortex Amygdala Cortisol Pituitary Hypothalamus Hippocampus Effects of Chronic Stress Adrenal Gland Cortisol
- 17. 17
- 18. My contact info: Jordan Greenbaum, MD Cell: 404-790-0499 jordan.greenbaum@choa.org call anytime! 18
Editor's Notes
- “How does childhood adversity impact adult well-being? The role of toxic stress”In this workshop we will discuss the links between early childhood maltreatment and other adversity, and long term emotional and physical health consequences in adulthood. We will look at the role of toxic stress in brain development during childhood and adolescence. We will discuss ways to help build resilience in children, and strategies to help adults work with traumatized children and youth. Objectives: Recall the results of the adverse childhood experiences studies that demonstrate links between childhood trauma and adult health outcomes Understand how toxic stress affects brain development throughout childhood and adolescence Recall factors that increase resilience in children who experience trauma
- Most neurons are present at birth, except hippocampus (new cells produced lifelong) Neurons migrate as circuits develop Primitive functions mature, or nearly so, at birth (breathing, heart rate control) 400 gm at birth, to 1000 gm at 12 months By age 3, brain is 90% adult size Volume of brain increases more during first 12 months of life than during any other period From birth to 5 years, brain triples in mass Myelination proceeds at different rates in different regions. Is very protracted process for prefrontal cortex; very early and rapid for vital motor systems Development proceeds from b stem to cortex (for example, the executive functioning of frontal lobes) Very important connections between centers in brain stem and areas of cortex, so much regulation comes from b stem. Maturation involves new cells, new connections, pruned connections, turned on genes, turned off genes, etc
- Different areas mature at different times, rates Effect of an experience on brain development depends on when the experience occurs (since maturation is varying over time) Age-appropriate experiences: you can’t teach a 6 mo to read—his brain isn’t ready for that. Areas controlling lower order functions (ex, vision: color, shape, movement, light) mature early, usually before or shortly after birth Higher order function areas(ex, recognizing familiar objects, recognizing facial expression) depend on development of lower order areas (so if maldeveloped this can affect maturation of higher order areas) Many higher order function areas have not begun, or are in early stages of maturing by age 3.
- A period during which…. Period of sensitivity is limited Duration of period varies, there is overlap; low level circuits have earlier periods Different areas of brain have different sensitive periods for development Sensitive period may be triggered by the progress of development or by intense impulse activity related to experience
- Sensitive periods end when conditions causing state of plasticity no longer operate or operate with less efficiency. Some plasticity continues after the period ends, and the amount varies with the circuit. Changes in the circuit that occur after the sensitive period ends must operate within the constraints set by the sensitive period Sensitive periods may end abruptly (imprinting) or gradually (language acquisition) But adult plasticity doesn’t involve significant structural change, is mostly involving increasing efficacy of certain connections Complex behaviors involve many circuits and problems with lower level circuits may be partially compensated for by development in higher level circuits (sensitive period has stayed open longer) Plasticiity continues throughout life, but to maximize benefit, you need to activate the relevant circutis and actively engage (attend to ) the task.
- Important in executive functions, including attention, working memory, control of impulsivity, response selection, planning, reasoning, decision-making and coordination of info from other parts of the brain It uses info from the limbic system to guide behavior (ex, amygdala) (we need emotion to decide on our behavior) PFC develops all the way into adolescence and early adulthood; different areas develop at different rates. Cingulate cortex and dorsolat PFC are higher order cortical areas and mature last. ACC is thought to be involved in the need for control and in conflicts between cognition and emotion. The ventromedial PFC is especially important in decision-making and for processing reward and punishment. When damage involves this area, adults have impairments in impulsivity, social behavior, planning and decision-making and cannot learn from prior experiences.
- 2 major stress response systems: Fast system: sympathetic-adrenal-medullary axis: release catchols and get FFF response Slow system; limbic-hypothalamic-pituatary=adrenal axis
- Sympathetic system is responsible for "fight or flight" response, corresponds with arousal and energy generation, and inhibits digestion. Diverts blood flow away from the gastro-intestinal (GI) tract and skin via vasoconstriction. Blood flow to skeletal muscles and the lungs is not only maintained, but enhanced (by as much as 1200% in the case of skeletal muscles). Dilates bronchioles of the lung, which allows for greater alveolar oxygen exchange. Increases heart rate and the contractility of cardiac cells (myocytes), thereby providing a mechanism for the enhanced blood flow to skeletal muscles. Dilates pupils and relaxes the lens, allowing more light to enter the eye. Provides vasodilation for the coronary vessels of the heart. Constricts all the intestinal sphincters and the urinary sphincter. Inhibits peristalsis.
- Sympathetic response: RAPID ONSET fight or flight: rapid heart rate, increased blood pressure, sweating, etc. mobilizes energy stores redirects blood flow to organs necessary for flight/fight Sympathetic response is within seconds HPA: hypothalamus secretes CRH…anterior pituatary secretes ACTH….adrenal cortex secretes glucorticoid (cortisol) glucorticoid is secreted within minutes and effects last hours mobilizes energy stores regulates gene expression in neurons involved in modulating stress responsiveness, emotion and memory cortisol causes some change by affecting gene transcription and this can take hours.
- There are different ways to define ‘prefrontal cortex’ and they suggest differing sizes for the PFC (e.g., smaller area than above)
- Impact of stressful event on a child depends on degree of stress response provoked and duration of response These depend on past experience with stress and ameliorating factors (like supportive adult) Prolonged elevations leads to changes in architecture affecting learning and memory Regulates gene expression in neurons involved with modulating stress responsiveness, emotion and memory
- the neural circuits for dealing with stress are particularly malleable (or “plastic”) during the fetal and early childhood periods. Early experiences shape how readily they are activated and how well they can be contained and turned off. Toxic stress during this early period can affect developing brain circuits and hormonal systems in a way that leads to poorly controlled stress-responsive systems that will be overly reactive or slow to shut down when faced with threats throughout the lifespan. increases in the level of cortisol in the brain actually can turn specific genes “on” or “off” at specific times and locations. Examples include regulation of the glucocorticoid receptor gene, which affects the long-term responsiveness of the brain to stress-induced cortisol release, and the myelin basic protein gene, which is involved in regulating the development of the “insulation” that increases the efficiency of nerve signal transmission. High, sustained levels of cortisol or corticotropin-releasing hormone (crh), which is the brain chemical that regulates the hpa system, result in damage to a part of the brain called the hippocampus. This can lead to impairments in learning, memory, and the ability to regulate certain stress responses in both young and adult animals. Individual responses to early stressful experiences can vary dramatically. This variability is thought to be related to differences among animals in the expression of so-called “vulnerability genes,” which make it more likely that early stressors will lead to subsequent problems in stress hormone regulation and behavioral difficulties. In such cases, positive early caregiving can decrease the likelihood of these adverse outcomes, demonstrat- ing that beneficial environmental influences can moderate the impact of genetic vulnerability.
- Child generalizes fear response to situations that may vaguely resemble original fearful event, so has anxiety, fear, and perceives threat even in situations that are non-threatening. May misinterpret facial expressions, statements, gestures, actions as dangerous and react to them in a way that is inappropriate to the real situation. Can lead to anxiety, PTSD, withdrawal, aggression. Chronic stress impairs functioning of PFC so this impairs child’s ability to attend to tasks, learn (impairs working memory), control emotions If cannot keep data in working memory, cannot learn effectively; to learn must be able to fix attention, and shift attention appropriately Infants are able to learn to fear certain conditions. But they are very vulnerable since they cannot remove the danger, have immature responses to stress, have difficulty regulating their emotions anyway. If no supportive caregiver, situation is even worse. Fear-conditioning can lead to impaired stress response and affect stress response in future Fear-conditioning doesn’t just go away over time, without effort. simply removing a child from a dangerous environment will not by itself undo the serious consequences or reverse the negative impacts of early fear learning. There is no doubt that children in harm’s way should be removed from a dangerous situation. However, simply moving a child out of immediate danger does not in itself reverse or eliminate the way that he or she has learned to be fearful. The child’s memory retains those learned links, and such thoughts and memories are sufficient to elicit ongoing fear and make a child anxious. Science clearly shows that reduc- ing fear responses requires active work and evidence-based treatment. Children who have been traumatized need to be in responsive and secure environments that restore their sense of safety, control, and predictability—and supportive interventions are needed to assure the provision of these environments. Where indicated, children with anxiety can benefit from scientifically proven treatments, such as cognitive behav-ioral therapy, which have been shown to reduce anxiety and fear.
- If you chronically infuse cortisol in rats, you get upregulatin of amygdala acitivy, biasing function toward rapid, emotion-charged fight/flight/freeze responses, while at the same time downregulating paraventricular activity, resulting in normal to hyporesponsiveness of the HPA axis. Cortisol acts on the amygdala, hippocampus, PFC and CC. Animal studies show that chronic stress is associated with overgrowth of dendrites in amygdala and atrophy of dendrites in mPFC (there is bidirectional communication between these structures normally) Adults with PTSD have difficulty with this modulation between cortex and limbic system, so are hypervigilant at all times, even when no threat is around. They also demonstrate decreased mPFC activity and increased amygdala activity There is a co-occurrence of problems with mPFC fxning and stress responsiveness and this likely reflects interactions between neuroendocrine stress systems and frontal functioning. mPFC helps regulate behavioral, endocrine and autonomic responses to stress. Abused kids with PTSD have been show to have general deficits and deficits in executive functions (PFC domain). Interestingly, maltreated kids have not shown problems with memory processes that are associated with hippocampal functioning. Imaging studies suggest an impact on the development of the mPFC in maltreated kids (reduced white matter in the PFC and CC). Studies indicate that chronic stress (maltreatment) increases both the learning and the expression of ‘fear-learning’ (develop fear response to innocuous stimulus) and decreases the ability of the PFC to control fear-related responses. Stress-related changes to the PFC are reversible potentially, but those to amygdala are not. Will kids experiencing chronic stressors necessarily have low cortisol levels? Unlikely. Rather, we might expect that acute psychosocial stressors could still produce large HPA axis responses in chronically stressed maltreated kids. Study of 7-13 yo depressed, abused kids: With CRF challenge, there were two groups having different responses (level of ACTH response): one group was normal to hyporesponsive; the other was hyper=responsive. Kids in the latter group were experiencing continued, ongoing emotional abuse (not seen in other group).