When isolated, young rhesus macaque monkeys make a cooing sound to attract their mothers.


When a person is present, but not staring at the monkey, they tend to freeze in place and look around warily.


This warning snarl sends a clear message from a monkey who's being stared at -- back off or else!

  Posted 30 Apr 1998. Few behaviors are more hard-wired into the human psyche than fear. And it's a good thing, too. Fear of outsiders keeps members of animal troops safe from rivals. Fear of predators protects against crushing canines and masticating molars.

Knowing that fear is not one thing, but several, could help doctors treat excessive or inappropriate fear.But the paralyzing fear some kids feel when they start school, or the cold sweat that prevents some people from flying can be undesirable and inappropriate.

For 20 years, Ned Kalin, a psychiatrist at the University of Wisconsin-Madison, has studied fear in people and monkeys. In a talk this April before the Fourth Annual Wisconsin Symposium on Emotions, sponsored by the HealthEmotions Research Institute at Madison, he explained that monkeys have a palette of fearful, or defensive, behaviors that are controlled by different brain mechanisms.

Each winter (no fools, these!), Kalin and colleagues Steven Shelton and John Berard study a free-living colony of primates called Rhesus macaques on a 38-acre islet called Cayo Santiago off the coast of Puerto Rico. Over the years, they noticed that the monkeys responded differently to different threats.

Many kinds of fear
Working in a lab back in Madison, Kalin and Shelton put young macaques through three tests, and saw three adaptive (appropriate) fearful responses.

  1. When left alone for 10 minutes, most of the monkeys started cooing to attract their mothers' attention. Being separated from mother terrifies infant primates, so this is a smart, adaptive reaction.
  2. When a human intruder entered the room and looked away from the monkey, most of the animals skulked toward the back of their cage and froze. Such freezing minimizes the chance of being detected and gives the animal time to figure out what to do.
  3. When a person stared expressionless at the monkey, the animal started a kind of "defensive aggression" reaction, with deep barking, bared teeth, and rattling the cage. Staring, Kalin notes, can be very threatening, since it can signify that a predator has located you or that another member of your species is trying to dominate you.

So far, so good. But why did some monkeys freeze for a few seconds, and others for minutes at a time? Why did 5 percent of the pre-adolescent monkeys freeze when they were stared at, while 95 percent got aggressive? (Remember, freezing makes sense before the animal is discovered, but it can be fatal if a hawk or tiger has already located it.)

To further define these types of fearful behaviors, Kalin gave small amounts of drugs to the monkeys. He found that opiates inhibited the cooing for the mother (which made sense since opiates made naturally by the body are known to affect attachment behavior) but not the aggressive barking. Anti-anxiety drugs like diazepam, or valium, had little or no affect on cooing, but it did decrease barking and freezing.

Most mothers are relaxed, even when scientists snap their portraits.

But the mother on the right is chronically tense. Could the monkey's behavior tell us something about human behavior?

All photos courtesy of Ned Kalin, University of Wisconsin- Madison.

What does all this mean for people plagued by fear and anxiety disorders? For one thing, that fearful responses combine several elements; fear is not one single thing. For another, the problem is not simply having too much emotion, Kalin says, but of having the wrong one, or being unable to hit the "off" switch. "People in the past have conceptualized problems of emotions as being overly intense responses. But we find animals that are unable to turn off a specific reaction, or which express the wrong reaction."

Mind and body, or mind is body?
Kalin is one of many neuroscientists who are finding a strong link between biology, emotions and behavior. Did you catch our coverage of emotions and health?

In the long run, the on-going monkey studies should lead to a more exact picture of fear and anxiety disorders. "We hope to understand the biology of how the brain works," says Shelton, "and when things go awry, what aspects are affected."

Kalin adds that fear behaviors in the monkeys have analogs in people. For example, freezing in place, "may be a model for extreme shyness in children, which increases your risk of developing anxiety or depression later in life." In the broadest view, the monkeys' message is this: Fear has its flavors. "We know that fear-caused behavior is not the same," Kalin says. "We have different responses."

The Why Files covered fear, but we're afraid you missed it.

-- David Tenenbaum

Selected readings: The Neurobiology of Fear, Ned Kalin, Scientific American, May, 1993, pp. 94-101.

The Regulation of Defensive Behaviors in Rhesus Monkeys: Implications for Understanding Anxiety Disorders, Ned Kalin and Steven Shelton, in Wisconsin Symposium on Emotion, RJ Davidson (ed.), Oxford University Press, in press as of May, 1998).

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