Theory of mind deficits in patients with acquired brain injury: a quantitative review.

Impaired theory of mind (ToM) reasoning is considered an underlying cause of social cognition deficits in patients with acquired brain injury (ABI). However, the literature does not agree on the severity of ToM impairment in this clinical population, nor does it coincide on the proper tools for its assessment. In this paper, we use a meta-analytic approach to review 26 studies which compare the performance of ABI patients and healthy controls in four widely-used ToM tasks: first-order belief task, second order belief task, understanding indirect speech (IS) and social faux pas. Overall, patients show moderate to severe ToM impairment. The latter appears in faux pas (effect size=0.70) and understanding IS tasks (ES=0.87), while moderate impairment can be seen in second-order (ES=0.60) and first-order belief tasks (ES=0.52). The severity of ToM impairment was influenced by ratio of patients with frontal lobe lesion, ratio of patients with right hemisphere injury, type of belief task, and heterogeneity of the sample's etiology. Our results provide important quantitative evidence on the severity of ToM deficits in the ABI population, while identifying variables that influence these deficits. Implications for basic and clinical neuropsychology are discussed.