Anthropologists and researchers at the Yerkes National Primate Research Center are making groundbreaking advances towards the understanding of the human brain by comparing humans with chimpanzees.

Both Associate Professor of Neuroscience at Yerkes Todd Preuss and Assistant Professor of Anthropology James Rilling began looking at the chimpanzee brain during the mid-1990s.

Rilling, who did his Ph.D. dissertation at Emory, said that he and then-director of Yerkes and current director of the National Institute of Mental Health Thomas Insel “initiated the first project to collect magnetic resonance imaging (MRI) scans from primate species, which indirectly tells us about human brain evolution.”

“As an anthropologist, I’ve always been interested in human evolution,” Rilling said, adding that the “greatest mystery of all is the evolution of the human mind and brain and how we became different from other species.”

Preuss also said that his interest rested with the way human brains aren’t like those of other animals and that understanding those differences requires comparison.

“The most powerful comparison is with our closest relative, the chimpanzee,” Preuss explained.

Researchers have long considered the close relationship between humans and chimpanzees an important one to study.

“To show that something is uniquely human, we need to show that it is not present in chimpanzees,” Rilling said.

Preuss and Rilling’s project is a part of a larger brain aging project led by Research Professor of Neuroscience at Yerkes James Herndon. The project contains four different components studying various areas of neuroscience, including Preuss and Rilling’s work.

The comparative studies between chimpanzee brains and human brains have been made possible with new techniques and technologies within the last decade.
Diffusion tensor imaging (DTI) allows researchers to see the diffusion of water in tissue, which yields neural tract images and provides an image of higher resolution than one a traditional MRI would show.

There is little information about the human brain because most studies concerning the brain involve non-human animal species.

“It’s been very difficult to study human brains and chimpanzee brains,” Preuss said. “We now have the new techniques, and, for the first time, we’ve been able to do these comparative studies.”

The research has yielded brand new and interesting results, Preuss said, and added that “it’s a very exciting time.” According to Rilling, this data can help researchers identify what it is about the human brain that allows for abilities such as the use of language.

The study of aging between human beings and chimpanzees has proved particularly interesting because life spans differ between the two species. According to Preuss, “with respect to aging, humans are very interesting animals because we can live for a long time, and this has been true throughout most of time.” On the other hand, he added, chimpanzees rarely make it past 60 years of age.

The ability of the human brain to remain intact is incredible because when tissue expends the amount of energy that the human brain does, it suffers a lot of damage. In order to repair that damage, humans must have ways to keep the “neurons in the brain humming,” throughout one’s lifetime.

Preuss and Rilling’s project looks at the difference in life span and the variance in the damage suffered and damage repaired between humans and chimpanzees.

According to an article on the study in the April 2 issue of Science Magazine, Alzheimer’s disease does not appear to affect chimpanzees, which may help identify how the human brain functions.

“Identifying what it is about human aging that’s different might help us understand why we’re more susceptible to neurodegenerative diseases than chimpanzees,” Rilling explained of the overall project to which his and Preuss’s work is contributing.

The main focus of Preuss and Rilling’s project right now is to look at the patterns of connectivity within the brain and to understand how the brain is wired, Rilling said, but the new discoveries are paving the way for additional research.

“My primary goal has always been to learn about human nature and human evolution, but as we learn about the human brain, these are techniques we can apply to human disease,” Rilling said.

The method in which Preuss and Rilling test the animals, Rilling said, is non-invasive.

“We’re not using any procedure that we wouldn’t use with people,” he said. In addition to the scans, Preuss and Rilling are also working with language, tool use and other aspects of physical and social behaviors that vary among species.

There are “decades of work to do,” Rilling said, but he is worried that the research may not be possible in the distant future.

Preuss said that Yerkes, which is the “only place in the world where we [Preuss and Rilling] can do this kind of research,” is no longer breeding the chimpanzees because National Institutes of Health (NIH) is no longer funding the animals.

Rilling said that because there are many limitations on the types of research that can be done with chimpanzees for ethical reasons, there is not enough research that can be done for the NIH to support the breeding of chimpanzees.

In order to continue their research in the long term, the researchers are looking for both policy change and alternative sources such as funding from private donors, Preuss said, because chimpanzees have proven to be “extremely valuable for understanding the human brain.”

Rilling said that the research will not be possible once the chimpanzees are gone.

“The chimpanzees are getting older, and we’re really going to lose out on that opportunity to learn about human nature and human evolution,” Rilling said.

—Contact Alice Chen.