Emotion researchers study unique monkey colony

They seek insights into personality traits best suited for coping with stress

CAYO SANTIAGO — This 45-acre Caribbean islet is just a short motorboat ride off the Puerto Rican coast, but it is altogether another world. Only monkeys inhabit it.

Top: Ned Kalin, chair of the UW Medical School psychiatry department, focuses on some of the Cayo Santiago monkeys, who are the subject of emotions research. Kalin heads the UW–Madison Medical School Health Emotions Research Institute. Middle: A television crew picks its way along the 45-acre island off Puerto Rico. The television documentary, to air in May, is expected to detail development of emotions in animals, and features research from around the world. Bottom: A young monkey clings to an adult’s back. Research focuses on about 100 adolescent male monkeys during the normally stressful time when they must leave their mothers and peers.

For more than 50 years since they were first introduced from their native India, nearly 1,000 rhesus macaques have thrived on the rocky preserve, with its palm and mahogany trees and other lush vegetation. The monkeys have lived relatively undisturbed by all but a handful of humans, those who regularly bring supplemental food and study primate behavior in the wild.

Scientists from the UW–Madison Medical School Health Emotions Research Institute are among those privileged few. For the past three years, they’ve been studying the monkeys of Cayo Santiago to better understand how an individual’s temperament may affect the way he or she copes with stress.

Recently, representatives of the Discovery Channel accompanied the UW team, filming the monkeys in their natural tropical habitat and learning about the research. The television documentary, to air in May, details development of emotions in animals, and features research from around the world.

“Cayo Santiago is a highly unique, natural setting in which to study primate behavior,” says institute director Ned Kalin, who is also chair of the UW Medical School department of psychiatry. “It offers a different, complementary perspective to the work we have been conducting for years at the Wisconsin Regional Primate Research Center on the biology of fear.”

Kalin expects investigations on Cayo will reveal whether certain personality traits — such as being sociable — may lower vulnerability to stress, helping some people avoid disease. Monkey brains are organized in fashion very similar to human brains, he adds.

He and colleague Steve Shelton and their collaborators in Puerto Rico have been focusing on some 100 adolescent male monkeys during the normally stressful time when they must leave their mothers and peers and attempt to enter another unfamiliar group of monkeys. Up to 20 percent of them die during this challenging period.

“Our goal is to understand the relationship between the stress caused by the event and the monkeys’ emotional state and physical health,” says Kalin, who is the Hedberg professor of psychiatry and psychology.

The UW researchers monitor monkeys’ overall behavior and interaction with mothers, siblings and peers to identify those who are most sociable and those who avoid interactions and may be fearful.

Once a year, Shelton oversees a team that collects spinal fluid and blood samples indicating levels of stress hormones and immune function in the animals. EEGs are used to assess brain activity related to various kinds of temperament.

In their first round of data analysis, the group has found that monkeys with the highest levels of certain stress hormones tend to be less interactive and more fearful, while animals with lower levels of stress hormone are more interactive and often more aggressive.

“Our objective is to be able to identify monkeys at risk of dying during the time they separate from their mothers,” says Kalin. “Then we hope to be able to identify physiological characteristics and brain activity that may be responsible for making them vulnerable.”

Hurricane Georges recently roared directly over Cayo, he added, with winds registering 120 miles per hour. But no monkey deaths or injuries have been reported.