Brothers, Leslie A. “A Neuroscientific Perspective on Human Sociality."

In “A Neuroscientific Perspective on Human Sociality,” Leslie A. Brothers describes recent findings on the neural substrate of social behavior. A wide variety of evidence points to the role of the amygdala in processing information crucial for social interactions: (1) Monkeys with experimental lesions of the anterior temporal lobes (where the amygdala is located) have particular difficulty responding to the social signals of other monkeys. (2) Human patients with lesions of the amygdala have difficulty interpreting facial expressions, direction of eye gaze, and tone of voice. (3) Tests during neurosurgery show that a person’s ability to identify facial expressions can be disrupted by electrical stimulation to temporal-lobe regions. (4) Researchers studying vision in monkeys found temporal-lobe neurons that seemed to be responsive only to social visual stimuli such as faces. Brothers’ own research involved recording the activity of individual neurons in the region of the amygdala while monkeys watched video clips of other monkeys engaged in a number of activities. Her results showed that some nerve cells are particularly attuned to respond to movements that bear social significance, such as the specific yawn that males use to signal dominance.

The picture that is emerging from human and monkey studies, says Brothers, is that representations of features of the outside social world are first assembled in the temporal lobe cortices of the primate brain. Meaningful social events are registered when a host of signals and relevant contextual information are integrated. Our brains need to tell us the difference between someone approaching with friendly intent and someone whose aims are hostile, for example. The visual features of a face have to be put together to yield an image of a particular individual so that past interactions with this individual can be recalled. Next, movements of the eyes and mouth indicate the person’s disposition. Information from head position and body movement tell where this person is looking or going, providing raw material for the representation of a mental state such as his or her goal or desire. As these processes are taking place, the neural representation of others’ social intentions must be linked to an appropriate responsive behavior in the perceiver. Response dispositions should be set into play “downstream” from the temporal cortices, where face-responsive neurons have been found, in structures such as the amygdala. The amygdala, together with several other interconnected structures, receives sensory information and in turn projects directly to somatic effector structures such as the hypothalamus, brainstem, and primitive motor centers, making it a candidate for the link between social perception and response.

Brothers notes that human social interaction depends on the ability to employ the concept of person - a mind-body unit. What the research summarized here suggests is that the evolution of our brains has made it possible for us to construct and participate in the language-game of personhood; we have brains specially equipped for social participation.

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