Selective impairment of reasoning about social exchange in a patient with bilateral limbic system damage

Abstract

Social exchange is a pervasive feature of human social life. Models in evolutionary biology predict that for social exchange to evolve in a species, individuals must be able to detect cheaters (nonreciprocators). Previous research suggests that humans have a cognitive mechanism specialized for detecting cheaters. Here we provide neurological evidence indicating that social exchange reasoning can be selectively impaired while reasoning about other domains is left intact. The patient, R.M., had extensive bilateral limbic system damage, affecting orbitofrontal cortex, temporal pole, and amygdala. We compared his performance on two types of reasoning problem that were closely matched in form and equally difficult for control subjects: social contract rules (of the form, ''If you take the benefit, then you must satisfy the requirement'') and precaution rules (of the form, ''If you engage in hazardous activity X, then you must take precaution Y''). R.M. performed significantly worse in social contract reasoning than in precaution reasoning, when compared both with normal controls and with other brain-damaged subjects. This dissociation in reasoning performance provides evidence that reasoning about social exchange is a specialized and separable component of human social intelligence, and is consistent with other research indicating that the brain processes information about the social world differently from other types of information.

Investigating Behaviour and Face Encoding in a Hypothetical Real-World Social Contract: Handwashing in Hazardous Health Settings

“…This effect was also found for unfamiliar social contracts (Cosmides 1989), and has since been observed crossculturally (Sugiyama et al 2002). Furthermore the difference in cognitive processing of social contract over abstract tasks is further supported by the differences in performance of patients with brain damage (Stone et al 2002) as well as the finding that emotional processing predicted reasoning on social contract tasks but not abstract ones.…”

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