Are The Brains of Apes "Ready" For Language?

Gannon, P.J., Holloway, R.L., Broadfield, D.C., and Braun, A.R. (1998) Science, 279, 220-222.

Overview:

Language and Brain

Language is generally considered a uniquely human ability. Animals communicate, but only humans have an abstract system of symbols and rules that allows sharing of just about any kind of information.

The human brain appears to be specially "wired" for language. Two areas of the left cerebral cortex have been identified as important for language. Wernicke's area lies along the planum temporale of the left hemisphere, tucked away along the sylvian fissure. This area of the brain appears to be essential for understanding and producing words. Broca's area lies in the left posterior part of the inferior frontal lobe and appears to be important for grammar.

Karen/Vicki - Can you get a diagram of this???

These two brain areas have been identified by studying people with damage to these parts of the brain. People with damage to one or both of these areas have specific language difficulties called aphasia. People with damage to Wernicke's area have problems finding the correct words to say. Their speech may sound quite normal in terms of intonation but makes no sense; they also have great difficulty understanding what is said to them. These people have Wernicke's aphasia. People with damage to Broca's area speak in very short sentences or in single words, very much like young children. Their sentences are meaningful and they can understand speech relatively well. These people have Broca's aphasia.

Wernicke's and Broca's areas are larger in the left hemisphere than in the right hemisphere in most people. Gannon, Holloway, Broadfield, and Braun (1998) examined the area corresponding to Wernicke's area in chimpanzee to determine if their brain structures showed the same asymmetry between the hemispheres. Asymmetry in a Wernicke's area in chimpanzee brains might have interesting implications for the evolution of language.

Article Summary

Do apes have language? Even if they can't "speak" to us, can they learn our language? Do they have the brain structures necessary for learning language? Gannon, Holloway, Broadfield, and Braun (1998) looked at brain structures in our closest primate relative, chimpanzees (Pan troglodytes), to see if they have one of the brain structures that is essential for human language.

In humans, Wernicke's area in the left cerebral cortex is essential for receptive language. This area is much larger in the left hemisphere than it is in the right hemisphere; this asymmetry is larger than any other brain structure. Because language is considered unique to humans, it is widely assumed that the asymmetry in Wernicke's area is also unique to humans.

Gannon and his colleagues measured the area of a part of chimpanzee brains that corresponds to Wernicke's area in humans. They obtained 18 chimpanzee brains. Of these, 15 were in good enough shape to manipulate. Gannon et al. spread apart the brains at the sylvian fissure which separates the temporal lobe from the rest of the cortex. They then measured the surface area of Wernicke's area, also called the planum temporale, using anatomical guides developed with humans. In 14 of the 15 brains they could measure, the left planum temporale was larger than the right. In many brains the area was even visibly much larger and extended further back along the lobe.

Gannon et al. suggest several reasonable evolutionary explanations for the asymmetry they found, including:

• The asymmetry could have been totally unrelated to language in some common ancestor to both the chimpanzee and human. The left planum temporale evolved to serve a language function in humans but some totally unrelated function in chimpanzees.

• The asymmetry could have been related to some language/communication function but evolved in humans to serve a language function and some other communication function in chimpanzees. Gannon et al. suggest that the numerous studies of cognitive and communication abilities of chimpanzees supports this hypothesis.

Gannon et al.'s finding raises interesting questions about evolution of brain structures and their relationship to the evolution of behavior.

For Instructors

Links to the Lecture

WNET, a PBS station in New York, has developed a series called The Mind. Part 7: Language considers language from a biological, evolutionary, and developmental perspective. It provides a good link to the research article and a jumping off point for a discussion about human versus nonhuman language.

The Mind: Part 7: Language (1988, WNET/New York, 60 Min.).

For Students

About the Authors

Patrick J. Gannon is an otolaryngologist, Ralph L. Holloway and Douglas C. Broadfield are anthropologists, and Allen R. Braun is a language and communication neuroscientist. Interdisciplinary research such as this study of chimpanzee brains often yields very interesting findings.

About the Journal

Science is a very prestigious journal that publishes a wide range of scientific articles. Check out abstracts and recent science news.

Links to Life

This is an ABC News article about a signing orangutan. Chantek can sign a lot of words and makes unique combinations of words but does he have language? Professor Laura-Ann Petitto has been studying apes and sign language in order to better understand the development and functions of language. Dr. Irene Pepperberg has observed that her African grey parrot, Alex, makes up new words.

TIPS is a computer language program. Have a conversation with the computer. Is this language?

This course on linguistics from the University of Pennsylvania has very good descriptions of Wernicke's and Broca's aphasias, including language samples produced by people with each type of aphasia.