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Planet of the Communicative Apes...and Humans
chimpanzee and human
Did the PT evolve a functional role in communication-related tasks in chimpanzees, as it did in humans?


MRI Coronal slice MRI of planum temporale on left side.

Dr. Gannon notes that he and Dr. Allen Braun obtained preliminary evidence from anatomic magnetic resonance images of chimp brains from the Smithsonian Institution before making the discovery of left larger than right Planum Temporale on cadaver brains by direct inspection.


Famed bonobo Famed bonobo "Kanzi" at the Language Research Center at Georgia State University.

Dr. Gannon describes Kanzi as "an incredible individual who understands a lot of human spoken language and is able to communicate via lexigrams." In their upcoming work, Dr.'s Gannon, Braun and colleagues plan to monitor the activity of "language" regions in the brain of a bonobo such as Kanzi with PET scans, as the ape responds to communication-related tasks. If PT becomes activated on the left hemisphere, proof of its role in "language" outside of the human realm will be demonstrated. Will this then represent an ape version of Noam Chomsky's human "language organ"? Gannon says, "We don't think so!"

 

Gestures, grunts and hoots may not rival a Shakespeare sonnet, but the area of the brain generating this jungle-wild language of chimpanzees is structurally the same as the communications-oriented part of the human brain called planum temporale (PT). This brain region may attend to processing communicative information regardless of its modality- gestural/visual, physical/tactile, vocal/auditory, or otherwise - and is thought to be an epicenter within a dispersed mosaic of language-related regions in the cerebral cortex.

planum temporale
Sylvian fissure spread open on both sides to show left hemisphere predominance of planum temporale size.
The PT is widely accepted as a key component of Wernicke's language area of the brain, and is linked to behaviors presumed to be distinctly human including musical talent and handedness, as well as communication disorders such as schizophrenia and dyslexia. Language sites on the left hemisphere, which may also include the PT, are also used by people born deaf who use sign language.

The planum temporale is normally bigger on the left side of the brain (called "left hemisphere predominance") and is more pronounced than any other human brain asymmetry. The PT and its particular characteristics in controlling communication behaviors are widely accepted by scientific communities as being uniquely human.

Patrick Gannon
Patrick Gannon.
New groundbreaking research twists the tale. Led by Dr. Patrick Gannon of the Mount Sinai School of Medicine Department of Otolaryngology and supported by the NSF Physical Anthropology Program, researchers' findings reveal that the anatomical pattern and relative size of the PT in chimpanzee brains parallels humans precisely. Gannon argues that this evidence likely means that the anatomically distinct PT was already a fundamental neural substructure in the brain of a human - great ape (chimp, orangutan, gorilla) common ancestor around 8-14 million years ago. In fact, Dr James F. Battey, Jr., Director of NIH-NIDCD, has stated in an NIH press release "This study will generate language research from a new perspective."

The researchers believe that this pre-hominid brain trait diverged in its evolution from chimps when early human ancestors moved from their limited, localized territories to become wide-ranging bipeds in a busy world that demanded novel communication skills. Dr. Gannon contends that, apparently, "this area of the brain doesn't care where the information is coming from -- just that it's communication."

human brainWhile chimpanzees are our closest relatives with 98% similarity in genes, we clearly have a different take on communication. Chimps clap, wave, pick at each other tenderly, tickle, play, wrestle, gaze into each other's eyes and issue utterances to each other that some scientists feel constitute a complex chimp language that may be facilitated by a subtle "gestural-visual" mode different from that used by humans and thus incomprehensible to humankind. Dr. Gannon says "Chimpanzees have a sense of self, a great cognitive capacity to understand a lot of things we teach them and the neurophysiology behind their communication ability is likely similar to our own."

Other scientists interpret the new evidence to mean that while chimps and other great apes may have more complex communications systems than previously thought, these systems still don't constitute language. They believe that while we may have a fundamentally similar ancestral brain area, the PT region did not evolve a functional role in communication-related tasks in chimpanzees as it did in humans, and that it serves some other purpose.

While further research will illuminate the debate, the Mount Sinai research suggests that functions of the PT further evolved independently in humans and chimps to serve each species' growing cognitive and communicative needs. The scientific methods used by the Mount Sinai investigative team include:
  • MRI (Magnetic Resonance Imaging) with 3-D, computerized images analysis. This process is helping reveal more detailed evidence of homologous relations between the cerebral cortexes of great apes and humans.
  • Immunocytochemistry, the selective staining of cell parts of the brain, in this case the planum temporale in human, ape and macaque brain tissue samples, to study the potential for asymmetric distribution of various brain chemicals that would further support parallels to the human condition.
  • Forthcoming PET (positron emission tomography) scans, in collaboration with Dr. Allen Braun of the Language Section, Voice, Speech and Language Branch, NIH - National Institute on Deafness and Other Communication Disorders and the Language Research Center at Georgia State University, to study the brains of chimps and bonobos (sometimes called pygmy chimps) in action, communicating their way through the day.

This particularly newsworthy research reveals insights into the origins of human language and speech, including the organization of language-related areas of the brain and their design, origin and evolution. It also raises ethical challenges for neuroscience and other research which utilizes living apes. Dr. Gannon says, "I don't know if you've ever met a chimp, but they are pretty amazing creatures, very sophisticated!"

For more information please see:

"Asymmetry of Chimpanzee Planum Temporale: Humanlike Pattern of Wernicke's Brain Language Area Homolog". Patrick J. Gannon, Ralph L. Holloway, Douglas C. Broadfield, and Allen R. Braun Science 1998 January 9; 279: 220-222.


This research is funded by Physical Anthropology.

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