Male rhesus monkeys with destroyed amygdala will abandon their normally slow and cautious familiarization process and immediately approach other monkeys with whom they are unfamiliar, according to David Amaral, professor of psychiatry and neuroscience at the University of California, Davis. His study on these animals is slated to appear in an upcoming issue of Behavioral Neuroscience. The study involved six lesioned monkeys, each meeting for many 20-minute sessions with a "stranger" monkey. The lesioned monkeys, their guards down, groomed and immediately presented themselves for sex to the other monkeys. The lesions, said Amaral, suggest that the amygdala, a brain structure about the size of half a thumb, plays a role in evaluating whether a situation is dangerous. The amygdala, he says, has connections with higher brain regions such as the cerebral cortex, enabling the latter to "attend to a particularly salient stimulus." Unlike intact monkeys, the lesioned animals showed...

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