Frontotemporal contributions to social and non-social semantic judgements

Semantic judgements involve the use of general knowledge about the world in specific situations. Such judgements are typically associated with activity in a number of brain regions that include the left inferior frontal gyrus (IFG). However, previous studies showed activity in brain regions associated with mentalizing, including the right temporoparietal junction (TPJ), in semantic judgements that involved social knowledge. The aim of the present study was to investigate if social and non-social semantic judgements are dissociated using a combination of fMRI and repetitive TMS. To study this, we asked participants to estimate the percentage of exemplars in a given category that shared a specified attribute. Categories could be either social (i.e., stereotypes) or non-social (i.e., object categories). As expected, fMRI results (n = 26) showed enhanced activity in the left IFG that was specific to non-social semantic judgements. However, statistical evidence did not support that repetitive TMS stimulation (n = 19) to this brain region specifically disrupted non-social semantic judgements. Also as expected, the right TPJ showed enhanced activity to social semantic judgements. However, statistical evidence did not support that repetitive TMS stimulation to this brain region specifically disrupted social semantic judgements. It is possible that the causal networks involved in social and non-social semantic judgements may be more complex than expected.