Differential Impairment of Cognitive and Affective Mentalizing Abilities in Neurodegenerative Dementias: Evidence from Behavioral Variant of Frontotemporal Dementia, Alzheimer's Disease, and Mild Cognitive Impairment

Cognitive and affective theory of mind (ToM) can be impaired in the course of neurodegenerative dementias. Experimental tests based on different task conditions and/or complexity may fail to capture disease-specific patterns of impairments. In this study, we assessed with a single task both the affective and the cognitive facets of ToM ability in a sample of 47 patients (i.e., 12 AD, 20 bvFTD, and 15 aMCI fulfilling IWG criteria for AD in predementia phase) and 65 healthy controls. Subjects were administered the Story-based Empathy task (SET), a non-verbal task measuring the ability to infer others' intentions (IA) and emotions (EA) compared to a control condition (causal inferences, CI). Global and single sub-condition scores were evaluated with a vectorial method, analyzing the relationship between social abilities and basic cognitive functioning by means of two indices representing the basic ability to perform the task and the balance between basic functions and ToM skills. Dementia (AD and bvFTD) patients showed impaired performances on all SET sub-conditions, whereas aMCI subjects' performance was not different from healthy controls. Vectorial analysis revealed a specific change in the balance between EA and CI conditions only in the bvFTD group, supporting a disproportionate deficit in mental states attribution based on affective cues. The overall deficit in the task in AD appears to be more general and related to the severity of dementia. This latter finding is further supported by the normal performance of the prodromal AD group.