Cognitive and olfactory changes in aging

Abstract

Age is associated with decrease in several cognitive functions whereof some changes may indicate a beginning pathologic process resulting in a state of dementia. The papers included in the thesis addressed questions related to cognitive and olfactory changes in elderly individuals with an aim to gain knowledge on the influence of the Apolipoprotein E (ApoE) ε4 allele on cognition and to extend the understanding of the association between cognitive functioning and odor identification performance. The first paper investigated the impact of the ApoE ε4 allele on cognitive functioning in a sample of non demented elderly individuals recruited from a population with a high prevalence of this allele. Paper 2 addressed the question whether the Scandinavian Odor Identification Test (SOIT) and its cut-off scores for diagnosis (hyposmia and anosmia) is applicable and valid to be used in Norwegian samples of middle aged and older individuals. The occurrence of olfactory dysfunction was further investigated in the third paper. It was examined whether individuals who were unaware of an olfactory dysfunction performed lower on cognitive tasks compared to individuals with normal olfactory function. In paper 4, the interrelation between different odor identification tasks (familiarity, cued and free odor identification), their association with cognitive measures as well as age-related performance differences were investigated. The present thesis shows that deficits in cognitive performance, demonstrated in verbal learning and memory tasks, can be related to the ApoE ε4 allele. The papers on olfactory functioning revealed the applicability of the SOIT in the elderly segment of the Norwegian population. It was shown that olfactory dysfunction increases with age and that changes often remain unnoticed. Individuals unaware of their olfactory dysfunction performed lower on a number of cognitive measures. The ability to identify odors was associated with a varying number of cognitive measures depending on the demands of the task. In conclusion, this thesis strengthens the generality of previous findings demonstrating an association between ApoE ε4 and impaired performance on verbal learning and memory tasks. The findings indicate further that odor identification performance is associated with a number of cognitive measures, predominantly episodic memory functioning. Odor identification tasks may provide valuable information in the examination of elderly individuals at risk for pathological decline.