Theory of mind in individuals with Alzheimer-type dementia

Background: Theory of Mind (ToM) ability allows attribution of mental states to oneself and others. Recent studies suggest that impairment of ToM may be a partial cause of social-communication impairment in adults with right hemisphere disorder, frontal lobe damage, and the frontal variant of frontotemporal dementia. Initial evidence has also been presented for a ToM impairment in individuals with Alzheimer's disease (AD), but extant investigations have inadequately controlled for other cognitive impairments. Aims: The purpose of this study was to determine whether individuals with AD exhibit a ToM impairment that is distinguishable from cognitive and executive function deficits, and to investigate whether memory support affects their ToM performance. Methods Procedures: Ten participants with mild to moderate AD completed first-order and second-order false belief tasks with and without memory support, and their performances on ToM testing were compared to those of elderly controls. All ToM testing was controlled with memory, comprehension, and general inferencing questions. AD participants completed neuropsychological testing to concurrently assess general cognitive functioning, memory, and executive functioning. Independent and paired t-tests compared experimental and control group ToM performances. Correlations assessed relations between ToM and neurocognitive test performances. Outcomes Results: Results indicated that, in the absence of memory support, AD participants did not exhibit a specific ToM difficulty as compared to control participants. However, significant group differences for specific ToM impairment that appeared to be separable from comprehension, memory, and general inferencing difficulties emerged during ToM testing when memory support was provided. Correlations between ToM performance and neurocognitive test performances were not significant; however, four of the eight AD participants who exhibited specific, ToM difficulty also had difficulty with executive function testing. Conclusions: These results indicate that individuals with mild to moderate AD may possess an underlying, mild, specific ToM impairment, which becomes apparent during supported memory testing. Such mild ToM impairment in moderate AD individuals must be further investigated, and possible contributions of executive function impairments to apparent ToM difficulty further explored before the current results can be confidently generalised to a larger AD population.