In the first study of its kind, researchers at the Yerkes National Primate Research Center, Emory University, used functional brain imaging to assess resting-state brain activity in chimpanzees as a potential window into their mental world and to compare chimpanzee brain activity to that of humans.
The researchers' findings suggest chimpanzees may engage in thought processes similar to those of humans at rest as well as thought processes that are quite different. The findings are significant because they show the uniqueness of humans as well as our similarity to our closest living primate relative.
According to lead researcher Jim Rilling, PhD, "Examples of resting-state thoughts are when your mind wanders to past social interactions, to potential future social interactions and to problems you need to solve."
Working with his research team and using positron emission tomography (PET), Rilling studied eight humans and five chimpanzees. Results showed significant overlap in brain activity patterns such as high levels of activity in the medial prefrontal and medial parietal cortex, brain regions associated with reflecting on mental states of self and others. Results also showed differences with humans, including activity in regions associated with language and the analysis of meaning; these were found in humans but not chimpanzees.
The research team included Yerkes, Emory College and/or Center for Behavioral Neuroscience colleagues Sarah Barks, Todd Preuss, PhD, and Lisa Parr, PhD.
"Widespread activity in language regions of the human brain suggest humans think with words, though, of course, chimpanzees do not," says Rilling.
In choosing to image resting-state brain activity, the researchers reasoned if the pattern of brain activity in chimpanzees at rest is similar to humans, there is likely to be some similarity in cognition; conversely, they thought, if there are differences in brain activity during rest, it would imply differences in resting-state cognition.
"This study bears on important issues in comparative psychology, specifically whether chimpanzees understand other beings have minds. This study doesn't resolve the issue, but it does suggest humans and chimpanzees share brain systems involved in thinking about one's own behavior and that of others," Dr. Preuss adds.
Researchers plan to further study chimpanzee brain activity by imaging the animals while they are engaged in tasks that specifically drive mental processes the researchers hypothesize to be ongoing at rest.
Results appear in the online Early Edition of the Proceedings of the National Academy of Sciences.