Cognitive and affective theory of mind in Lewy body dementia: A preliminary study

'Theory of Mind' refers to the ability to attribute mental states, thoughts (cognitive component) or feelings (affective component), to others. This function has been studied in many neurodegenerative diseases; however, to our knowledge no studies investigating theory of mind in dementia with Lewy Bodies (DLB) have been published. The aim of our study was to search theory of mind deficits in patients with DLB. Seven patients with DLB (DLB group), at the stage of mild dementia or mild cognitive impairments, and seven healthy elderly adults (control group) were included in the study. After a global cognitive assessment, we used the Faux Pas Recognition test to assess the cognitive component of theory of mind, and the Reading the Mind in the Eyes test for the assessment of affective component. We found a significant difference between the two groups for the Faux Pas test with an average score of 35.6 for the DLB group and 48.3 for the control group (P=0.04). Scores were particularly low in the DLB group for the last question of the test concerning empathy (42.9% versus 85%, P=0.01). There was not a significant difference between the two groups for the Reading the Mind in the Eyes test (P=0.077). This preliminary study showed early impairments of theory of mind in the DLB. The cognitive component seems more affected than the affective component in this pathology. This pattern is consistent with the pattern found in Parkinson's disease, but differs from other neurodegenerative diseases as Alzheimer's disease or frontotemporal lobe dementia. These patterns may help to differentiate DLB from these diseases. Further study is needed to confirm these results and to compare with other dementias.