Researchers at the Yerkes National Primate Research Center have found the area in the chimpanzee brain involved in the production of chimpanzee manual gestures and vocalizations is similar to what is known as Broca's area in the human brain. The study, available in today's online edition of Current Biology, is the first to directly link chimpanzee and human brain areas associated with communicative behaviors, suggesting chimpanzee communication is not only more complicated than previously thought, but also that the neurobiological foundations of human language may have been present in the common ancestor of modern humans and chimpanzees.
In the human brain, Broca's area is one of several critical regions associated with gestures and speech. Human functional imaging studies have shown significant patterns of activity in this area during language-related tasks. Lead researcher Jared Taglialatela, PhD, set out to determine if chimpanzees would show comparable patterns of activity in an area of the brain anatomically similar to the Broca's area.
"We were interested in determining the neurobiological underpinnings of chimpanzee communication, as a number of behavioral studies indicate chimpanzees intentionally produce manual gestures, as well as some types of vocal signals, to communicate with humans," said Taglialatela.
For the study, three chimpanzees each participated in two different tasks. For the communication task, a researcher sat outside the chimpanzees' home enclosures with pieces of food. After a set period of time, the researcher took the food and left the chimpanzee area. When the researcher was present, the chimpanzees produced gestures and vocalizations to request the food.
For the baseline task, the researcher again approached the enclosures with food, but this time, chimpanzees received small stones to exchange for pieces of food. After returning a fixed number of stones, each chimpanzee was rewarded with a small piece of food.
"The chimpanzees were not communicating with the researcher in this task; they were simply returning stones," says Taglialatela. "We included this task to make sure we really were looking at neural activity associated with communicative signaling and not simply normal motor behaviors," he continues.
During each task, researchers used positron emission tomography (PET) to monitor chimpanzee brain activity. Both tasks showed significant brain activity, but researchers found considerably greater levels of activity during the communication task as compared to baseline in an area of the brain similar to Broca's area.
Taglialatela says, "One interpretation of our finding is that chimpanzees have, in essence, a language-ready brain. Our results support that apes use this brain area when producing signals that are part of their communicative repertoire."
Researchers plan to further study chimpanzee brain activity by examining chimpanzee perception of communication through the use of prerecorded chimpanzee vocalizations. Additionally, researchers will attempt to determine whether the observed activity in the brain is a result of manual gesture production, vocal production or, as is the case with humans, a result of the production of communicative signals, independent of modality.
For more than seven decades, the Yerkes National Primate Research Center, Emory University, has been dedicated to advancing science and to improving human health and well-being. Today, the center, as one of only eight National Institutes of Health-funded national primate research centers, provides specialized scientific resources, expertise and training opportunities. Recognized as a multidisciplinary research institute, the Yerkes Research Center is making landmark discoveries in the fields of microbiology and immunology, neuroscience, psychobiology and sensory-motor systems. Resea rch programs are seeking ways to: develop vaccines for infectious and noninfectious diseases, such as AIDS and Alzheimer's disease; treat cocaine addiction; interpret brain activity through imaging; increase understanding of progressive illnesses such as Parkinson's and Alzheimer's; unlock the secrets of memory; determine behavioral effects of hormone replacement therapy; address vision disorders; and advance knowledge about the evolutionary links between biology and behavior.