This document discusses how the human brain develops and is shaped by experiences and the environment. It specifically focuses on how stress affects brain development. Key points: - The brain is plastic and adapts to experiences, especially during windows of development when neurons proliferate, migrate, differentiate and prune back connections. - The hypothalamus-pituitary-adrenal axis regulates the stress response through cortisol and CRH, which shape the brain's stress system, especially receptors in the hippocampus and amygdala. - Dysregulation of the stress response, resulting in high and prolonged cortisol levels, can impact emotional regulation and academic performance. Nurturing experiences during development help establish a robust stress response system.

1. Stress and Human
Development
OT 513 Prof. White

2. An interesting story to tell with far too many
chapters (e.g. examples) that get written over
and over again in human history.
Why do we think it insignificant when we don’t care
about the well-being of ALL mothers and children?
General purpose of this next topic is to
convince you of the significance of this question.

3. First, we need to learn a bit about how the
human brain develops…
• Key principles include:
–Plastic (adaptable)
–Excess neurons initially
–Pruning (cutting back) with purpose
–Windows close but never shut completely

4. How nurture with nature…
how the environment shapes one’s given genetic
and structural constitution

5. The
Developing
Human Brain
Source: Adapted from Cowan, 1979.

12. https://www.youtube.com/watch?v=vyNkAuX29OU

13. Neurons
• PROLIFERATE: increase in number in the fetus
• MIGRATE: move to various regions of the brain in
the fetus
• DIFFERENTIATE: increase in size, complexity, and
functioning in the infant

14. The Migration of Neurons via Glial Fiber
(about 24-26 weeks gestation in utero)
John Karapelou/©1998. Reprinted with permission of Discover Magazine.

15. Neurons (cont’d)
• PRUNE BACK: To only used connections in the
older infant/young child
• CONTINUE: To make new connections
throughout adulthood, but in smaller numbers
than in the child

17. Two Types of Neural Plasticity
(meaning “change”)
• Experience-expectant:
– neurons begin to grow and differentiate rapidly, adapting to
experiences that are “expected” in development
• Experience-dependent:
– sensitivity of neurons to specific events or experiences,
adapting brain structure in response to new experiences

18. Cross-Section of the Human Brain
Remember the
hypothalamus-
pituitary-adrenal
axis? Hippocampus
Amygdala

19. Hippocampus
Pituitary
Hippocampus
Amygdala
hypothalamus
Thalamus
Area of
Hypothalamus
and Thalamus
(not shown)

20. Amygdala

22. The HPA…
• Produces two critical
hormones/neurohormones/neurotransmitters
1. CRH
2. Cortisol
• Remember …
• Hypothalamus releases CRH to the pituitary
• Then pituitary releases ACTH to the adrenals
• Adrenals then release cortisol into bloodstream for general circulation
• In 15-20 minutes post-stressor, cortisol is in saliva.
• The HPA system is up and running early in
development
• These two---CRH and Cort---become critical in shaping the
brain’s stress response system
(Kirschbaum et al.; Larson, White, Gunnar)

23. Cortisol, well regulated, looks like:
Dysregulated cortisol expression (not typical) can look
like:
*too high, overall
*too high in evening and night
*too low overall
*too low in am

24. Blair & Razza (2012) Scientific American Mind. [NIH/NICHD]

25.  Dysregulation can result in a response then a slow
return to baseline (too high for too long).
 In Blair & Razza’s work –previous slide--Cortisol
levels in saliva tend to follow one of four patterns in
people’s response to stress.
◦ Research indicates that emotional regulation, self-control
and academic performance are tied to the typical pattern,
in which cortisol rises in response to stress and falls again
when the stressor is gone.
◦ Consistently high levels of cortisol as well as blunted
responses to stress are linked with poor self-control and
academic difficulty.

26. CRH and CORTISOL
Play the largest role in stress brain development.
How do we create that lovely, robust, well-regulated and
adaptive on/off capability?
• EXPERIENCES….but special kinds. 
• On/off capability of the HPA in response to threat
Quick, adaptive responding to
stressors linked to hypothalamus
and hippocampus receptors for CRH/cortisol
• CRH - finds it way into parts of the hippocampus and
the amygdala.
• Why would the hippocampus be aligned with cortisol?

27. CRH and CORTISOL
• Stressful experiences shape the number and
location of these receptors in the hypothalamus
and hippocampus
oBaby rats and mommy ‘breaks’ that are normative vs
prolonged
oWhat is the important factor? Being away from mom or
mom’s behavior when you return?
• What are normal stressors for babies? What
can we study if human babies react similarly?
Hint….In US, boy babies often have?
• Two studies that helped shape our understanding
of the young stress response system

28.  Please make sure to check into your
assignments on Canvas and follow
instructions for videos and readings.