Inhibited monkeys feel the brunt of stressful times

Elevated stress caused by confinement made highly inhibited Rhesus Macaques more vulnerable to attacks by other members of their troop, according to a study published in Health Psychology (Vol. 17, No. 3, p. 285?289).

For two years, researchers observed 21 male and 15 female monkeys that had been living together for nine years in a 5-acre outdoor habitat. During the study?s first year, the monkeys had unhindered access to their free-range environment, which included wooded and cleared areas, a pond and several enclosures. Using behavioral measures, researchers classified some troop members as behaviorally inhibited?they were fearful, socially isolated and withdrew from new objects and peers.

During the next six months, researchers confined the monkeys to a 1,000-square-foot cinder block building while their habitat was under renovation. The building provided a high-quality care environment. However, there was nowhere for the animals to hide if they wanted to withdraw from the group.

The average number and severity of injuries increased five fold during the confinement period, with injuries to highly inhibited troop members accounting for most of the increase, the study finds. The researchers used veterinary records to ascertain the number and character of injuries and found that many appeared to be caused by violent attacks by other monkeys. The rate of injury returned to normal when the troop returned to the free-range habitat.

Other studies find that risk of being attacked increases when inhibited macaques withdraw from a challenge. Therefore, having no place to hide during the confinement period may have increased inhibited monkeys? risk of injury, the study authors propose.

The study results indicate that differences in how individuals respond to stress may affect susceptibility to injury and disease, write the study authors.

?B. Azar