5 The Origin of Language and Primate Behavior
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| Kobayashi: The development of the brain in children is related to language in many respects. When you hand a device to adults, they will push each button and learn the functions one by one, but children will play around with it, and in the process, make it their own. Language is a typical example of something that is acquired in this way. |
Sawaguchi: You're probably right. In the past, there were two language areas: Broca's motor speech center and Wernicke's sensory speech center. Then there is the angular gyrus that is concerned with reading and writing, so there were at most three areas. However, recent neurobiology recognizes that there are a surprising number of systems that are related to language, and they operate in different situations.
In the past we did not know that the prefrontal association cortex was involved with language, but we now know that it has about three systems that are language-related. They function to control and organize abstract language, much like computer programming. The systems are not specific to language so this is not considered a language area per se, and the brain has a number of systems like this. The area itself is quite large so language systems occupy more of the brain than we had thought. |
| Kobayashi: And they function in many ways. |
| Sawaguchi: That surprised me somewhat. In addition, the right hemisphere is used quite a bit. |
| Kobayashi: The right hemisphere is said to be related to music, not language. |
| Sawaguchi: That is the prevailing view, but we now know that it is used quite a bit in language, too, in particular, for intonation and rhythm. |
| Kobayashi: Oh, sensory information. The mirror neuron system that is also used when we are engaged in mirroring behavior is controlled by Broca's motor speech center, too. |
| Sawaguchi: Yes. These mirror neurons can be seen in monkeys, too. |
| Kobayashi: Mirror neurons? |
Sawaguchi: Yes, this is one reason why we expect the primate research to be helpful in our research on language.
In monkeys, the area of the brain involved in opening the hands and grasping becomes active even when they are shown images and video of these same movements. In humans, when you ask them to name certain tools, the brain becomes active in the same way. This indicates that the motor system is involved in language. Furthermore, since the mirror neurons that are "mimicking neurons" are located nearby, and language acquisition starts with mimicry, the systems for mimicking and language seem to be found in the same area. In humans, this is the 45 area, in other words, the area that corresponds to Broca's motor speech center that is related to language.
However, other than chimpanzees, monkeys do not engage in outright mimicry. So, in the true sense of the term, the origins of mirroring can be traced back to the chimpanzee, but monkeys do engage in something similar to mirroring. When they see something like themselves, they react in a similar manner. The mirror neurons of monkeys are located in nearly the same area in humans that is related to mirroring behavior. I think we might be able to learn the origins of language by studying this area.
Monkeys do not learn language no matter what. This might be because they do not have a theory of mind and so their mirroring does not go beyond hand gestures.
To some extent, infant monkeys will mirror the eating gestures of the mothers, but if you point to your face and try to get them do the same, they can't. Chimpanzees, on the other hand, make pointing gestures right away. And they also exhibit shared attention. If you want them to turn right, they will turn their faces to the right. Chimpanzees will think that there is something they should pay attention to and turn to the right. |
| Kobayashi: All of them together. |
| Sawaguchi: Yes. In some monkeys, if one of them looks to the right, the others will do the same, possibly thinking that there might be an enemy in that direction or the opposite sex. I am not sure if this can be called mirroring, but it is similar and that is about the extent of what monkeys do. Chimpanzees, however, engage in more mirroring so if we see this behavior as a stage, we can infer that mirroring is important to human development and it might lead to mirroring of language. |
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Noboru KOBAYASHI, M.D.
Pediatrician and Director, CRN
Born in Tokyo in 1927. Doctor of Medicine, Faculty of Medicine, The University of Tokyo, 1954. Books include Human Science, Kodomo wa mirai de aru (Children are Our Future), Kodomogaku, Sodatsu sodateru fureai no kosodate (Reciprocal Development Through Child-raising).
Toshiyuki SAWAGUCHI, Ph.D.
Professor of Neurobiology, Hokkaido University School of Medicine
Born in Tokyo in 1959. Majored in biology, Faculty of Science, Hokkaido University. Doctor of Science, Kyoto University. Specializes in cognitive neuroscience and primatology. Research interests include mechanisms within the brain related to thought and self and evolution of the brain and cognitive function. Publications include Wagamama na no (The Selfish Brain), Watakushi wa no no doko ni iru no ka? (Where is the Self in the Brain?), and Yoji kyoiku to no (Early Childhood Education and the Brain).
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