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. 2020 Oct 14;70(1):48.
doi: 10.1186/s12576-020-00777-8.

The relationship between olfaction and cognitive function in the elderly

Sae Uchida  1 , Chiho Shimada  2 , Naoko Sakuma  3 , Fusako Kagitani  4 , Akiko Kan  5 , Shuichi Awata  3
Affiliations

The relationship between olfaction and cognitive function in the elderly

Sae Uchida et al. J Physiol Sci. .

Abstract

This study investigated the relationship between olfaction and cognitive function in 12 elderly people (age: 80.9 ± 1.6) living in the community. Olfactory function was assessed by the identification threshold for rose odor. Four cognitive measures consisting general cognitive ability assessed by Mini-Mental State Examination (MMSE), its sub-domains, and attentional ability assessed by drawing a line to connect the numbers consecutively (trail-making test part A; TMT-A), were assessed. Subjects with a higher olfactory threshold (≥ 5) declined more in the performance speed of TMT-A (73% ± 7%, p = 0.05) compared with those subjects with a lower threshold (≤ 4) (averaged value was set at 100%). Other cognitive statuses assessed by MMSE tended to decline in subjects with higher thresholds. Because attentional function relates to the basal forebrain cholinergic system, our results suggest that olfactory impairment links to the decline in cognitive function, particularly of attention-relating cholinergic function.

Keywords: Attention; Cognitive function; Elderly people; Odor identification threshold; Olfactory function.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1
Fig. 1
Relationship between attentional ability and odor identification threshold. a Method testing the attentional ability by drawing a line to connect the numbers (TMT-A). b Scatter plot of the relationship between attentional ability (time in s) and identification threshold for rose odor in all 12 subjects. The dots represent the values of an individual subject. Pearson's correlation coefficient r with p-value. c Comparison of attentional ability (time in seconds) between two groups of different olfactory ability, that is, low-threshold group (≤ 4) and high-threshold group (≥ 5). The horizontal lines and vertical bars show the mean and SEM values in each group. p = 0.05; the significant difference between low-threshold group (≤ 4) and high-threshold group (≥ 5) was tested by Mann–Whitney test
Fig. 2
Fig. 2
Comparisons of four cognitive measures in odor identification of high-threshold group. a: Attentional ability (performance speeds of TMT-A). b: General cognitive ability (MMSE, total score), c: orientation and verbal recall (MMSE, 13-item subset), d: other cognitive domains (MMSE, another 17-item subset). The averaged value was set at 100% in the low-threshold group (≤ 4), for each cognitive function. Columns a–d and vertical bars values were presented as means ± SEM in the high-threshold group (≥ 5)
See this image and copyright information in PMC

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