Disorders of taste cognition are associated with insular involvement in patients with Alzheimer's disease and vascular dementia: Memory of food is impaired in dementia and responsible for poor diet

Background: In dementia patients, dietary intake problems may occur despite the absence of swallowing problems. We investigated cognitive functions on food and taste in Alzheimer's disease (AD) and vascular dementia (VaD) patients. Methods: Participants included 15 healthy controls (HC), 30 AD and 20 VaD patients. Food Cognition Test: Replicas of three popular foods in Japan with no odors were presented visually to each participant, with the instruction to respond with the name of each food. Replicas of food materials were subsequently presented to ask whether they were included in these foods. Taste Cognition Test: Replicas of 12 kinds of foods were presented to describe their expected tastes. Results: The AD/VaD groups exhibited significantly lower scores on Food/Taste Cognition Tests compared with the HC group. These scores correlated inversely with Mini-Mental State Examination (MMSE) scores in the AD group. Decreased dietary intake was observed in 12 of the 50 patients; 8 of the 12 exhibited decreased Taste Cognition Test scores, higher than that of the normal-intake patients. There was no difference in the filter paper taste disc test between HC/AD/VaD groups. To test the hypothesis that the insula is associated with taste cognition, two MMSE-matched AD subgroups (n = 10 vs. 10) underwent positron emission tomography. Glucose metabolism in the right insula was lower in the low taste cognition subgroup. The VaD patients with insular lesions exhibited impaired Taste Cognition Test findings. Conclusions: It is important to consider the cognitive aspect of dietary intake when we care for dementia patients.