The Effect of the ApoE ε4 Allele on Recognition Memory for Olfactory and Visual Stimuli in Patients with Pathologically Confirmed Alzheimer’s Disease, Probable Alzheimer’s Disease, and Healthy Elderly Controls

Abstract

Episodic recognition memory for odors, faces, and unfamiliar symbols was assessed in apolipoprotein episilon4 positive and epsilon4 negative individuals with pathologically-confirmed Alzheimer's disease (AD), individuals diagnosed with probable AD, and healthy age- and gender-matched controls. The analyses revealed significant differences in performance between the AD patients and nondemented elderly controls based on the presence of the epsilon4 allele and the modality of the stimulus to be remembered. Measures of hits did not discriminate among groups but an analysis of false positive errors revealed significant differences, particularly for olfactory stimuli. Nondemented epsilon4 positive controls committed fewer false positive errors for olfactory stimuli compared to all other groups. In contrast, nondemented epsilon4 positive controls committed false positive errors for olfactory stimuli at rates similar to the AD patients. The performance of epsilon4 positive and epsilon4 negative controls was indistinguishable on the visual recognition memory tasks suggesting the particular vulnerability of olfactory memory to the early neuropathology of AD resulting in false positive errors in recognition memory for olfactory stimuli. The results of the present study offer new insight into how recognition memory is affected by AD, the epsilon4 allele, and the modality of the stimulus to be remembered.

Familiarity, Cued and Free Odor Identification and Their Association with Cognitive Functioning in Middle Aged and Older Adults

“…Our results confirmed earlier findings showing that familiarity is similar across age groups (Gilbert & Murphy, 2004;Larsson & Bäckman, 1997). Both odor identification tasks showed a decrease in performance with age.…”

“…The decline of cued odor identification performance often starts during the fifth (Doty et al, 1984a) and sixth decade of life (Brämerson, Johansson, Ek, Nordin, & Bende, 2004;Wehling, Espeseth, Reivang, Lundervold & Nordin, 2009). Findings are not consistent regarding familiarity: while Royet et al (2001) found that familiarity declined significantly with age, other authors have not confirmed this finding (Gilbert & Murphy, 2004;Larsson & Bäckman, 1997). Further studies of age effects in a sample performing different odor identification tasks are thus called for.…”

The effect of hormone therapy on olfactory sensitivity is dependent on apolipoprotein E genotype

“…The data suggest that the possible protective effect of HT on olfaction may diminish in the later stages of the disease. This result corroborates with other recent studies investigating differences in olfactory-related tasks between ε4 positive and negative non-demented older adults and AD patient populations (Gilbert & Murphy, 2004;Murphy et al, 1998). Generally, these studies have only found differences between ε4 genotype in AD onset and severity of symptoms in the very early, preclinical stages of AD but these differences seem to wash out in the middle to later stages of AD.…”

A comparison of discrimination and reversal learning for olfactory and visual stimuli in aged rats.

“…Furthermore, research studies have suggested that problems with remembering and detecting odors may be an early indication of cognitive impairment and dementing diseases in non-demented older adults (Devanand et al, 2002;Djordjevic et al, in press;Gilbert & Murphy, 2004b;Graves et al, 1999;Wang et al, 2002;Wilson et al, 2007). Although studies have examined odor learning in rats, it has not been clearly demonstrated whether odor learning is as affected by aging as visual learning in rats.…”