The Frontal Cortex

Over at Mind Hacks, Vaughan has a typically wonderful post on the "maternal impression" theory, which suggested that a psychological trauma inflicted on the pregnant mother would lead to profound defects in the unborn child. As Vaughan notes, this crude 19th century theory slowly faded away, as it became clear that birth defects had nothing to do with the mental state of the mother. But then, Vaughan says, the Soviet Union invaded Finland in 1939, and that all began to change.

The quickly assembled Finnish force was vastly outnumbered and ominously outgunned but, unlike their Soviet counterparts, they were quick and comfortable in the Artic conditions and made swift and deadly attacks.

In one of history's great military victories, they defeated the Russians but suffered heavy losses. Many of the dead were young men, and many of the grieving were young pregnant women.

Nearly 40 years later, two Finnish psychiatrists decided to look at the mental health of the children who grew up without fathers. They compared children born to women who grieved during pregnancy, to those born to women who lost their husbands after the child had been born.

Their study, published in 1978, found that mothers who had lost their husbands during pregnancy were much more likely to have children who later developed schizophrenia.

Many similar studies have found that severe maternal stress during pregnancy affects the developing brain of the child, increasing the risk of cognitive or psychiatric problems later in life, possibly due to the effect of the hormonal response of the hypothalamo-pituitary-adrenal (HPA) system.

Consider this depressing finding from the lab of Elizabeth Gould . She found that if a pregnant rhesus monkey is forced to endure stressful conditions - like being startled by a blaring horn for 10 minutes a day - her children are born with reduced neurogenesis, even if they never actually experience stress once born. This pre-natal trauma, just like trauma endured in infancy, has life-long implications. The offspring of monkeys stressed during pregnancy have smaller hippocampi, suffer from elevated levels of glucocorticoids and display all the classical symptoms of anxiety. Stress, in other words, has a way of lingering on.

From the perspective of the brain, this makes a crude sort of sense. After all, if you're mom was stressed when pregnant then you're probably being born into a tough world. Why invest in a lavish cortex, stuffed full of new neurons? It probably makes sense to err on the side of scarcity and anxiety.