A meta-analytic review of theory of mind difficulties in behavioural-variant frontotemporal dementia

Theory of mind (ToM) refers broadly to our understanding of others' complex emotions and mental states. Deficits in ToM are widely regarded as one of the key defining features of the behavioural variant of frontotemporal dementia (bvFTD), which is unsurprising given the key role that frontal and temporal neural systems are considered to play in mental state decoding. Here we report the first meta-analysis of this literature, providing a timely summary of the breadth, magnitude and specificity of ToM difficulties in this population. Across 15 datasets involving 800 participants (312 with bvFTD and for comparative purposes, 325 non-clinical controls and 163 participants with Alzheimer's disease), several key results emerged. Collapsed across all types of task, people with bvFTD performed more poorly than non-clinical controls, with the degree of ToM difficulty they experienced large in magnitude (r=-.60). These deficits were greater than those observed on control tasks matched to the ToM task in their general cognitive demands, but which can be solved without any mentalistic inference. BvFTD-related ToM difficulties were also significantly larger than the ToM difficulties seen in people with Alzheimer's disease. However, ToM difficulties in people with bvFTD were of a similar magnitude to the difficulties seen on measures of more basic social cue perception (emotion recognition). These data have important implications for understanding the types of ToM difficulties associated with bvFTD.