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 persons 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 persons
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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