Inference of mental states in patients with Alzheimer's disease

Introduction. The ability to determine what someone thinks or knows often requires an individual to infer the mental state of another person, an ability typically referred to as one's "theory of mind". The present study tests this ability in patients with mild-to-moderate Alzheimer's disease (AD). Methods. Three theory of mind tests and three standardised neuropsychological tests were presented to a group of patients with AD (n = 25) and a group of healthy elderly controls (n = 15). Results. On the first two theory of mind tasks, the performance of the AD patients was nearly perfect and did not differ from that of the controls: AD patients showed no difficulties in either attributing a false belief to another person, or in recognising their own previous false beliefs. On the third theory of mind task, where the key information was embedded in a story narrative, AD patients performed significantly worse than controls. However, their performance on this task was similar to the control condition, which used a similar story but which did not involve beliefs. Conclusions. These results, as well as those involving correlations between the neuropsychological tests and performance on the third task, suggest that the AD patients' difficulty may be secondary to their cognitive impairments, rather than a primary impairment in theory of mind.