Jan. 2, 2008 -- With their chattering, scampering ways, squirrels would seem to lead rather carefree lives, but a new study has found they can feel stress, and that its effects on the fluffy rodents are similar to its effects on people.
A certain amount of stress, which can cause a burst of energy, appears to improve reactions and learning ability, but too little or too much makes individuals -- both squirrels and humans -- go rather loopy.
The jittery vibe might even be the same.
"The feeling that comes with adrenaline when a cop's lights flash behind us is probably similar to the feeling a squirrel has when a hawk suddenly flies over, or when they hear an alarm call," Jill Mateo, author of the study, told Discovery News.
Mateo, an assistant professor in the University of Chicago's Department of Comparative Human Development, studied groups of Belding's ground squirrels at the Sierra Nevada Aquatic Research Laboratory. By placing cortisol in peanut butter and wheat germ treats, she artificially raised or lowered stress potentials in squirrels.
Cortisol is a hormone naturally produced by the body that raises blood pressure and blood sugar levels. Other studies indicate it provides energy to the brain, prompting the storage and retrieval of memories, Mateo said.
She focused her attention on juvenile ground squirrels. During their first month of life, they stay in cozy burrows with their mother. After this period, they go above ground and must fend for themselves.
That's when a lot of stress kicks in, and for good reason. Up to 30 percent of the young squirrels disappear during their first two weeks outside of the burrow, likely becoming dinner for hawks and other predators.
Mateo duplicated the challenges squirrels must face during this time in two ways. She put them through a maze that simulated the vegetation highways, rocks and logs that the animals would have to navigate through in the wild. She also paired the sound of a Brewer's blackbird alarm call, which warns of nearby raptors, with a Frisbee toss overhead.
The toss, Mateo said, "scares the bejesus" out of squirrels, which then usually "run for cover."
During her tests, however, only the squirrels with moderately elevated cortisol levels figured out the maze and swiftly escaped the Frisbee. Rodents with too little or too much cortisol had trouble learning.
The findings have been accepted for publication in the journal Neurobiology of Learning and Memory.
Prior research suggests the same thing happens to humans, though the challenges may be somewhat different. For example, a student who crams the night before a test and has a temporary boost in cortisol may benefit, but too little energy to the brain or too much can lead to poor concentration in the critical moment.
When we get older, the entire system can go out of whack.
Mateo explained that the brain winds up telling the adrenal gland to release cortisol, but the shut off-signal may become weaker as people age. As a result, "the brain swims in cortisol, but over time has fewer receptors for it and, surprise surprise, we have cognitive deficits."
Such elevated levels have been linked to Alzheimer's disease.
Research on stress in rats suggests possible treatments might focus on "an executive hub" at the front of the brain that quells the whole alarm process, which is centered deeper in the brain.
Steven Maier, a University of Colorado researcher, chemically inactivated this hub in the brainstem of rats, which then showed signs of depression and anxiety associated with uncontrolled stress levels.
But what about stress management?
"If an organism can cope behaviorally with an event, there's no need for intense physiological adaptation," Maier said.
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