Researchers at the University of Chicago have found the effect of stress-related hormone called cortisol. This could lead to the better understanding about the effect of this hormone on human beings too.
The study led by Jill Mateo, Assistant Professor in Comparative Human Development, has found that in normal survival tasks, ground squirrels would learn more quickly if they have a modest amount of cortisol, a hormone produced in response to stress, than those with either high or low levels of cortisol.
Mateo said that cortisol production in humans is linked to stress and also has an impact on learning. Though this impact is not well understood, this research on ground squirrels may lead to additional avenues of research.
Ground squirrels are required to adapt quickly for survival and should learn how to navigate the dangers of their environment so they can find their way back to their burrows. Usually ground squirrel pups come out from their burrows about the time they're weaned, at four weeks of age. In nature, about 30 percent of pups do not survive.
"Two hundred can emerge at the same time, providing a feast for predators," said Mateo.
His article, titled "Inverted-U shape relationship between cortisol and learning in ground squirrels," stated that modest levels of cortisol are apparently linked to the pups' survival.
The data forms an "inverted U" shape on a chart. While animals with low levels of cortisol are at the left of the inverted U, those with high levels are at the right, and the others with modest levels and higher learning are in the middle.
For testing if animals with low levels have difficulty learning, Mateo simulated a natural setting with a maze and connected it with a box that contained a nest of squirrel pups. She noninvasively altered the amount of coritsol in the pups' systems and found that those with both high and low cortisol levels took an average of 13 to 14 trials before they navigated the maze. On the other hand, a control group of non-treated pups with a modest amount of cortisol needed just nine.
Later, she tested the animals' response to danger by throwing a Frisbee over the maze and also by sounding a bird call to see how quickly the pups responded. High and low amounts of cortisol reduced the animals' ability to learn how to respond to danger.
However, unlike animals, researchers cannot moderate cortisol levels in humans to study its impact. However, scholars are aware of situations in which cortisol levels change due to unusual interventions and events. For example, for helping women at risk of pre-term birth deliver healthy babies, doctors sometimes treat them with synthetic glucocorticoids, which raise cortisol levels. The glucocorticoids facilitate foetal lung development.
"We know almost nothing about the neurobiological implications of these treatments on cognitive development of children," she said.
She also said that animal studies have shown that these treatments can have negative effects on brain development. Besides, not much is known about the impact of low cortisol on learning among humans.
Pregnant women who are exposed to stress, such as those tested after directly experiencing the collapse of the World Trade Center on 9/11, developed Post-Traumatic Stress Disorder and had significantly lower cortisol two years later, as well as their babies.
She said that animal tests also help to understand the potential human impact of low cortisol on learning.
The article is published in an on-line posting of the journal Neurobiology of Learning and Memory.