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Worried Sick: The High Price of Being Fearful
By Cheryl Simon Silver

Go ahead, worry about people who are always taking risks in life, going bungee jumping or hiking in the Himalayas. But while these people may end up in the emergency room now and again, being timid and fearful also has its costs—at least for rats.

Researchers have found that rats that are fearful in infancy maintain this trait throughout their lives and age prematurely, often dying young. The reason may be that they have higher levels of a stress hormone than other rats, and this takes a toll on their bodies.

Rat brothers in late middle age. The fearful one, left, suffers from a pituitary tumor.

Like rats, some people seek out novelty while others avoid it. Anxious, timid humans experience higher levels of a stress hormone called cortisol. Because people have long life-spans, the researchers tested the effects of high levels of stress hormones in timid rats.

By looking at pairs of brother rats, the researchers measured behavioral and physiological responses to novel stimuli throughout the animals’ lives as a model of what happens in people.

They found a connection between personality and health over the course of a lifetime.

“This tells me that there is something about personality traits that we have to consider in terms of health,” says researcher Sonia A. Cavigelli of the University of Chicago. “If a personality trait is stable over the lifespan and it has physiological implications, it is going to affect our aging process.”

Cavigelli and Martha K. McClintock, both psychologists at the University of Chicago, introduced rats, at three intervals in their life, to a novel environment reminiscent of the classic areas used in experiments testing how young children respond to new stimuli.

The researchers placed objects, such as a bowl, a tunnel, and a brick, into the exploration area, and videotaped how each animal moved about, and if and how it explored the object. Hormone levels were monitored regularly.

The novelty-loving rats explored new objects, whereas fearful rats did not. As children do when they respond to something frightening, like going to day care, the fearful rats experience high levels of adrenal hormone.

The hormones spiked in both bold and fearful rats when faced with novelty, but they stayed high in the fearful rats. Similarly, basal levels of the related stress hormone cortisol are elevated in fearful children.

Pulses of adrenal hormones can be beneficial, but prolonged high levels of the adrenal hormone known as glucocorticoid took a toll and caused premature aging. Overall, fearful rats died 15 percent sooner than their bolder brothers.

The findings, published in the Proceedings of the National Academy of Sciences, are the first in a long-term study. The researchers suspect that there is a bright side to fear of novelty.

“Fear of novelty looks bad for now,” says Cavigelli, “but in the prime of life, the novelty-loving guys might be more likely to go out into dangerous situations. I’d be hard pressed to say that fearfulness is a bad trait and we should get rid of it.”

Cavigelli also said that a few of the rats managed to change, shedding their fearful tendencies and becoming more adventuresome. She suggests that it may be possible to learn a new behavioral style—probably not from a brother but from a different role model who can get past pre-set notions about what kind of rat the individual tends to be.

Says Cagivelli: “It’s worth thinking about how we perceive the world and how that affects our physiology.”

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Cavigelli, S. and McClintock, M.K. Fear of novelty in infant rats predicts adult corticosterone dynamics and an early death. PNAS, 100, 16131-16136 (December 12, 2003).


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