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Research has shown that human bodily responses and cognitive shifts affect each other in both directions. We feel sorry because we cry, but also cry when feeling sorry. So, what then for our primate cousins? To date, their connections have remained largely unexplored.

Now a team of researchers at Kyoto University has led a study on six Japanese macaques living in KyotoU's Center for the Evolutionary Origins of Human Behavior, in Aichi prefecture. The researchers focused on self-scratching—a bodily response linked to negative emotions like anxiety and fear—and its relationship to pessimistic judgment bias, which is the tendency to expect a negative outcome when faced with ambiguous information. The findings are in the journal Proceedings of the Royal Society B: Biological Sciences.

By presenting the monkeys with a white rewarding button and a black non-rewarding button, together with a gray ambiguous button, the researchers were able to estimate each monkey's degree of pessimism. They also videoed the monkeys to identify the timing of self-scratching, analyzing the relationship between self-scratching and pessimism.

"Bodily responses associated with negative emotions can predict subsequent cognitive pessimism," says corresponding author Sakumi Iki, "but not the other way around."

In other words, the monkeys were more likely to make pessimistic judgments—avoiding the gray button—immediately after self-scratching, yet making a pessimistic judgment did not necessarily lead to self-scratching. This stands in contrast to humans, for whom evidence suggests a pessimistic way of thinking can cause bodily responses. That this influence did not appear in the macaques suggests that their emotional bodily responses may precede cognitive changes.

From an evolutionary standpoint, the coping strategy of first addressing immediate needs through bodily responses and then engaging in cognitive information processing is probably adaptive for dealing with challenges in natural habitats. Thus, this mechanism might have existed long before humans and macaques diverged, pointing to an evolutionarily conserved system.

"In humans, the relationship between mind and body may have evolved in a distinctive way, influenced by our use of language and advanced introspection," adds Iki.

"But it might be observable in monkeys if different bodily reactions or cognitive processes are examined."

Future research involving a wider range of primates and other animals could shed more light on the evolutionary origins of human emotions, and deepen our understanding of the connection between the mind and the body.