Olfactory event-related potentials in Alzheimer's disease

Areas of the brain affected in the early stages of Alzheimer's disease are also areas heavily involved in the processing of olfactory information. Olfactory event-related potentials (OERPs) and auditory ERPs were recorded from the Fz, Cz, and Pz electrode sites in 12 Alzheimer's disease (AD) patients and 12 age and gender matched normal controls (NC) in a single-stimulus paradigm with a 45 s inter-trial interval, using amyl acetate as the olfactory stimulus, and in a separate session a 500 Hz tone as the auditory stimulus. Odor identification (ID) was also used to assess ability to identify odors. The results indicate that (1) OERP P2 and P3 latencies were significantly longer in AD patients than normal controls; (2) olfactory ERP latency measures correlated significantly with dementia status as measured by the Dementia Rating Scale (DRS), indicating that as participants performed more poorly on the DRS, reflecting increased dementia, OERP latencies increased; (3) olfactory ERP latency measures better differentiated AD patients from normal controls than auditory ERP latency measures; (4) olfactory ERP measures alone correctly classified up to 92% of participants; (5) odor ID measures, namely the UPSIT and San Diego-Odor-ID tests also classified participants at a high rate. Combining scores for odor identification with olfactory P3 latency measures resulted in a correct classification rate of 100%. The results strongly support the use of olfactory measures in the assessment of AD.