Stress and Human Development

OT 513 Prof. White

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.

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

How nurture with nature…how the environment shapes one’s given genetic

and structural constitution

The Developing

Human Brain

Source: Adapted from Cowan, 1979.

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

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

The Migration of Neurons via Glial Fiber (about 24-26 weeks gestation in utero)

John Karapelou/©1998. Reprinted with permission of Discover Magazine.

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

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

Cross-Section of the Human Brain

Remember the hypothalamus-

pituitary-adrenal axis? Hippocampus

Amygdala

Hippocampus

Pituitary

HippocampusAmygdala

hypothalamus

Thalamus

Area of Hypothalamus and Thalamus (not shown)

Amygdala

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)

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

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

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.

CRH and CORTISOLPlay 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 threatQuick, 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?

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

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