Cortisol: Friend or Foe?

The much studied and much misunderstood hormone cortisol is generally an unwelcome visitor to a baby's developing brain. But research has show that as the child grows up, the brain actually requires small amounts of cortisol to mature. This is the final post in a series of three that I have written about an infant's brain development after reading Sue Gerhardt's excellent book "Why Love Matters".

Babies and toddlers rely on adults to regulate their emotional state. That is one of the reasons why it is so important for a child to have a constantly present attachment figure, though this does not necessarily have to be a parent. The child's very survival depends upon the attachment figure and consequently the child is extremely sensitive to the positive and negative messages given by the adult.

A parent's positive face tiggers off a pleasurable reaction in a baby. The baby's heart rate increases, and beta-endorphin and dopamine are released. Beta-endorphin is an opioid and dopamine is a stimulant so both make the baby feel good. Both also help the young baby's brain to grow by increasing the brain's uptake of glucose. This is why positive interaction with a young baby is so vitally important.

But the flip side of the baby's pleasurable reaction to a happy face is its negative reaction to an angry or sad face. Seeing a negative expression on its parent's face is itself a stressful event for a baby, triggering the baby's stress response. The stress response is sometimes described as the HPA axis, which is shorthand for "hypothalamus triggers pituitary gland which triggers adrenal glands". Each of these glands produce hormones, the most famous of which is cortisol, produced by the adrenal glands. Although there are several hormones involved in the stress response, it is cortisol that is the most widely studied because it can be measured in saliva.

It is accepted that during babyhood, cortisol is detrimental to the development of a baby's brain. Since babies are unable to self-regulate their stress levels, they require their adult caregivers to repeatedly return them to a state of equilibrium by meeting their needs for food, comfort, safety and love. But in toddlerhood, something interesting happens to the role of cortisol in the child's brain. A toddler actually needs some cortisol to complete the development of their orbitofrontal cortex - the part of the brain that controls how the child responds to basic emotions such as fear and anger. Gerhardt explains:

"Increased levels of cortisol facilitate the growth of norepinephrine connections from the medulla up to the prefrontal cortex. This delivery of norepinephrine helps the orbitofrontal cortex to mature further in toddlerhood, by increasing blood flow to the area and by forming its links (via the hypothalamus) with the parasympathetic nervous system. The parasympathetic nervous system is vital to the growing child, because this is the inhibitory system which enables the child to stop doing something and to learn what behaviour is unacceptable or dangerous."

The requirement for some brief does of cortisol coincides very neatly with the period in a child's life when it is becoming mobile and inquisitive, and often putting itself in danger. When the parents scold the child or simply stop it from doing something, their negative facial expressions set off the child's stress response, giving his body a quick shot of cortisol. However, too much cortisol would still be bad for the developing brain and so it is important that the parents once again restore the child to its emotional equilibrium state quickly.

Parents of toddlers apparently say "No" an average of once every nine minutes - but at least they can do it in the knowledge that they are performing an essential role in their child's development!

"Why Love Matters" is divided into three sections on brain development, the consequences of a dysfunctional childhood, and the way forward. The three posts I have written have all been based on material from the first section on normal infant brain development. But the whole book is a fascinating read and I would wholeheartedly recommend it. And if you have any book recommendations of your own, please tell me in the comments - I would love to read more well thought out, well researched books on parenting.

If you enjoyed this post, you may like to read the earlier posts on the book: Why Are Human Infants Born So Prematurely and Why It Is Wrong To Leave A Young Baby To Cry.