'Theory of mind' impairments and their relationship to executive functioning following frontal lobe excisions

It has been suggested that mental states play an important role in determin ing behaviour and that mental state attributions ('theory of mind') underli e the ability to understand and predict other peoples' behaviour. Theory of mind was investigated in 31 patients with unilateral frontal lobe lesions (15 right-sided and 16 left-sided) by comparing their performance with that of 31 matched control subjects. The ability to infer first- and second-ord er beliefs was tested by requiring subjects to listen to stories in which a protagonist acted upon a false belief. Both patient groups exhibited signi ficantly impaired performance on the two theory of mind measures. Both fron tal lobe groups also exhibited a range of deficits in tests of executive fu nctions, but analyses revealed that these seemed to be independent of theor y of mind impairments. These findings are discussed in terms of the hypothe sis of a specialized, adaptive brain system underlying theory of mind reaso ning ability, and are related to observed difficulties in social functionin g among patients with frontal lobe damage.