The Wake Forest University School of Medicine researchers also discovered more dominant monkeys undergoing the same stressful situation had fewer changes in brain activity in areas involved in stress and anxiety and were less likely to choose cocaine.

The brains of dominant monkeys and subordinate monkeys responded differently in both stressful and non-stressful situations

The scientists said their findings suggest monkeys that have to cope with constant, ongoing social stressors might have developed a lower level of brain activity even at rest.

In the abnormal situation of being placed in an unfamiliar cage surrounded by unfamiliar and aggressively behaving monkeys, however, the subordinate monkeys showed pronounced decreased brain activity in areas of their brain involved with stress, anxiety, reward and emotion while the dominant monkeys showed increases in reward-related areas in the same situation.

Robert Warren Gould, a graduate student in the laboratory of Professor Michael Nader, presented the study results Sunday in San Diego during Experimental Biology 2008.