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What is the "Social Brain"?

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For the fifth article in this Brain and Education series, rather than a topic from the journal MBE, I have chosen the "social brain" from a book entitled in Japanese "Social Brains: Recognition of the Self and Other" (Kazuo Hiraki and Toshikazu Hasegawa, ed., University of Tokyo Press). The term "social brain" is much talked about among psychologists, neuroscientists, and researchers in these fields today.

The term "social brain" is not one that necessitates particularly difficult conceptualization. The brain is equipped with various programs of the mind and body for everything from our physical movement to social life. The social brain is then considered to be that part of the brain which is the location of the programs of the mind required for conducting social life. It is interesting, however, to think about the disciplinary developments which established this concept. In this article, I offer a commentary on the above book along with my own thoughts on the social brain.

Undeniably, dramatic developments in evolutionary psychology, supplemented by advances in primatology, have lent much support to the idea of the social brain. Over the course of their long history, human beings have evolved while engaged in collective and then social life, which has gradually resulted in the development of a large and complex brain.

The primitive mammals that were our distant ancestors appeared on earth 70 million years ago. The evolution of these mammals indicates that arboreal primates evolved 20-30 million years ago and the Ramapithecus, which descended from the trees and walked upright, is thought to have appeared in Africa and Asia 14 million years ago. Around 7 million years ago, humans and the anthropoid chimpanzee, our closest relative with whom we share all but a few percent of our DNA, diverged from a common ancestor, and human evolution began its own path. During this time, ancestor of the chimpanzee that had split from human lineage is said to have separated into the present-day chimpanzee and bonobo 2 million years ago. The social life of these primates, in particular, that of anthropoids, provides many clues to our own process of socialization.

Thereafter, humans evolved into the Australopithecus 3.5 million years ago; the Pithecanthropus erectus, 2 million years ago; the Homo erectus pekinensis and Homo erectus erectus, 800,000 years ago; Homo neanderthalensis, 100,000 years ago; and then the Cro-Magnon Man, 40,000 years ago before becoming the present-day Homo sapiens who have built today's culture and civilization. In this process, the way of life changed from communal life to social life.

As mentioned in the first article of this series, 1. We Feel, therefore We Learn, the brain is thought to have first evolved in vertebrates, which means that the origin of our human brain can be found in the ancestors of fish and reptiles. Fish and reptiles today live in groups, so the ancestors of fish and reptiles must have lived in groups although it is hard to imagine that all primitive vertebrates did so. However, a prototypical communal life requiring the programs of the mind appeared after the emergence of primitive mammals, and after primates evolved, it quickly developed and grew in complexity into social life.

This has been corroborated by research in the comparative anatomy of the primate brain. The relative weight of the neocortex with its programs of the mind that control intellect and reason is considered to be related to the size of the collectivity where the particular primate experiences social life.

The development and increasing complexity of social life functions as selective pressure to drive evolution of the brain. From this, we can understand the evolution of the human brain from the "survival brain" of fish that swim leisurely in the sea, feeding on the small fish that enter their mouths, to the instinct-emotional brain of primitive mammals, and then to the intelligent-rational brain of higher mammals, including ourselves.

Research into autism has also given impetus to the concept of the social brain. Findings in the fields of psychology and cognitive science, such as the relation between the self and others and intention and gaze recognition, have, of course, greatly contributed.

Autistic children are characterized by deficits in interpersonal relations, communication, and imaginative play along with a localized scope of behaviors and areas of interest. They are considered to be either lacking in "theory of mind" or incapable of acquiring it. In other words, they are not equipped with the empathic skills to read the feelings of others. Given that they cannot form relationships or carry on a social life, this is a deficit of the social brain. As symptoms closely related to this, imitation and gaze following are not automatic or effectively used. These symptoms could indicate a deficit in the mirror neuron system related to the program of the mind for imitation, which has given rise to the "broken mirror" hypothesis.

Analysis of brain injuries and behavior following brain surgery also provide perspectives on the social brain. This was the subject of the second article in this series entitled 2. Lessons from the Development of Two Boys with Half their Brains, about the case of a construction worker injured in a railroad accident in the United States in 1848, which yielded important insight into this relation. Among numerous reports on symptoms following brain injuries or brain surgery, the article presents the cases of two boys, Nico and Brooke, who underwent removal of an entire hemisphere of the brain to control severe epilepsy at the age of three and eleven, respectively. These cases are important in that they suggest that hemispherectomy does not cause significant problems in children at a young age.

The concept of the social brain is shaped by the idea that the program of the mind that is necessary to conducting social life is located somewhere in the brain. It appeared in academic discourse in the mid-1980s. The term "social brain", however, was coined after neuroscience had made advances in social cognition and related areas of the brain were clarified (mainly, the amygdala, orbitofrontal cortex, and temporal lobe). Research on brain injuries and post-neurosurgery and the relation between autism in children and theory of mind have also been influential. As such, the concept of the social brain also has a significant role in resolving such problems as the increase in crime attributed to the development or abnormal development of sociality in children.

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