Olfactory memory in the old and very old: relations to episodic and semantic memory and APOE genotype.

The neuroanatomical organization that underlies olfactory memory is different from that of other memory types. The present work examines olfactory memory in an elderly population-based sample (Swedish National Study on Aging and Care in Kungsholmen) aged 60-100 years (n = 2280). We used structural equation modeling to investigate whether olfactory memory in old age is best conceptualized as a distinct category, differentiated from episodic and semantic memory. Further, potential olfactory dedifferentiation and genetic associations (APOE) to olfactory function in late senescence were investigated. Results are in support of a 3-factor solution where olfactory memory, as indexed by episodic odor recognition and odor identification, is modeled separately from episodic and semantic memory for visual and verbal information. Increasing age was associated with poorer olfactory memory performance, and observed age-related deficits were further exacerbated for carriers of the APOE ε4 allele; these effects tended to be larger for olfactory memory compared to episodic and semantic memory pertaining to other sensory systems (vision, auditory). Finally, stronger correlations between olfactory and episodic memory, indicating dedifferentiation, were observed in the older age groups.

The testing effect as a function of explicit testing instructions and judgments of learning.

During study, people monitor their learning; the output of this monitoring is captured in so-called judgments of learning (JOLs). JOLs predict later recall better if they are made after a slight delay, instead of immediately after study (the delayed JOL effect). According to the self-fulfilling prophecy (SFP) hypothesis delayed JOLs are based on covert retrieval attempts from long-term memory, and successful retrieval attempts in themselves enhance learning (the testing effect). We compared memory for 40 Swahili-Swedish paired associates after a week as a function of three different learning conditions, namely study plus (i) explicitly instructed self-testing, (ii) delayed JOLs, or (iii) less self-testing. We showed that repeated delayed JOLs lead to a memory improvement that does not differ significantly from a comparable condition where the participants are explicitly testing memory, and both the latter groups performed reliably better than a group that self-tested less. The results suggest that delayed JOLs improve long-term retention as efficiently as explicit memory testing and lend support to the SFP hypothesis.

Age-Related Olfactory Decline is Associated with the BDNF Val66met Polymorphism: Evidence from a Population-Based Study.

The present study investigates the effect of the brain-derived neurotrophic factor (BDNF) val66met polymorphism on change in olfactory function in a large scale, longitudinal population-based sample (n = 836). The subjects were tested on a 13 item force-choice odor identification test on two test occasions over a 5-year-interval. Sex, education, health-related factors, and semantic ability were controlled for in the statistical analyses. Results showed an interaction effect of age and BDNF val66met on olfactory change, such that the magnitude of olfactory decline in the older age cohort (70-90 years old at baseline) was larger for the val homozygote carriers than for the met carriers. The older met carriers did not display larger age-related decline in olfactory function compared to the younger group. The BDNF val66met polymorphism did not affect the rate of decline in the younger age cohort (45-65 years). The findings are discussed in the light of the proposed roles of BDNF in neural development and maintenance.

Cognitive factors in odor detection, odor discrimination, and odor identification tasks.

The purpose of this study was to determine cognitive correlates of olfactory performance across three different tasks. A total of 170 men and women (30-87 years of age) were assessed in olfactory sensitivity, discrimination, and identification. Also, participants were tested in a range of cognitive tests covering executive functioning, semantic memory, and episodic memory. Hierarchical regression analyses showed that proficiency in executive functioning and semantic memory contributed significantly to odor discrimination and identification performance, whereas all of the cognitive factors proved unrelated to performance in the odor threshold test. This pattern of outcome suggests that an individual's cognitive profile exerts a reliable influence on performance in higher order olfactory tasks.

Odor identification impairment in carriers of ApoE-varepsilon4 is independent of clinical dementia.

The ApoE gene is expressed in olfactory brain structures and is believed to play a role in neuronal regenerative processes as well as in development of Alzheimer's disease (AD), the most common form of dementia. The varepsilon4 allele has been reported to be associated with compromised odor identification ability in the elderly, and this deficit has been interpreted as a sign of pre-diagnostic AD. However, because it has not been demonstrated that the relationship between the varepsilon4 allele and odor identification is mediated by dementia, it is possible that the varepsilon4 allele may have an effect on odor identification over and above any effects of dementia. The present study investigated effects of ApoE-status on odor identification in a large, population-based sample (n=1236) of adults (45-80 years), who were assessed for dementia at time of testing and 5 years later. The results showed that the varepsilon4 allele was associated with an odor identification deficit among elderly participants (75-80). Critically, this effect remained after current and pre-diagnostic dementia, vocabulary, global cognitive status and health variables were partialled out. The present results suggest that the ApoE gene plays a role in olfactory functioning that is independent of dementia conversion within 5 years.