Human brain specializations related to language and theory of mind

Humans excel at transmitting ideas, skills, and knowledge across generations, and at building on those competencies in a cumulative manner. The transmission of our cumulative culture is assumed to depend on both language and mental perspective-taking, or theory of mind. If humans have specialized abilities in these domains, we must have neurobiological specializations to support them. Our research has used comparative primate neuroimaging to attempt to identify such specializations. The arcuate fasciculus is a white matter fiber tract that links Wernicke’s and Broca’s language areas. It is known to be involved in multiple, high level linguistic functions such as lexical semantics, complex syntax, and speech fluency. Using diffusion weighted imaging and tractography, we have demonstrated human specializations in the size and trajectory of the arcuate fasciculus that may partially explain human linguistic abilities. Theory of Mind depends on a set of cortical regions that belong to a neural network known as the default mode network that is functionally connected, highly active at rest, and deactivated by attention-demanding cognitive tasks. We and others have used functional neuroimaging to show that chimpanzees and other primates appear to have a default mode network that is similar to that of humans. However, the non-human primate default mode network seems to have weaker connectivity between certain key nodes, suggesting that these connections could play a role in human theory of mind specializations.