Taste impairment in Alzheimer's disease.

We conducted a study of Alzheimer's disease focusing on taste impairment to determine at which step of gustatory information processing (discriminativ e or perceptive, gnosic or associative, gustatory-verbal) possible perturba tions might be located. We used various foods found in a normal diet. Twenty patients and a matched control group participated in this study. The patients were divided into two subgroups according to disease severity (mi ld, moderate or severe). The study showed that patients with Alzheimer's di sease exhibited an impairment at all three levels of gustatory information processing. Impairment of discriminative and gustatory-verbal stages was more obvious i n the group of patients with severe Alzheimer's disease. Our study also sho wed that the gustatory deficiency can be described as an associative agnosi a in the mild stage of Alzheimer's disease. This concept is in line with th e notion of a dissociation between preservation of olfactory and gustatory thresholds and an alteration in odor identification in patients with mild s tage Alzheimer's disease, suggesting that the alteration is central rather than peripheral. Our findings suggest that an alteration of the associative level of gustatory information processing can be found in Alzheimer's dise ase early stage.