Olfactory and declarative memory performances are associated, as both functions are processed by overlapping medial-temporal and prefrontal structures and decline in older adults. While a decline in olfactory identification may be related to a decline in declarative memory, the relationship between olfactory detection threshold and declarative memory remains unclear. In this meta-analysis, we assessed (i) the relationship between olfactory identification/detection threshold and verbal declarative memory in cognitively normal older adults, and (ii) the effect of age on these relationships. We included articles from PsychNet, PubMed, and Academic Search Complete according to the following criteria: (i) inclusion of cognitively normal older adults; (ii) assessment of episodic or semantic memory; and (iii) assessment of olfactory identification or detection threshold. Seventeen studies and 22 effect sizes were eligible and included in this meta-analysis. Olfactory identification was associated with episodic (small effect size: r = 0.19; k = 22) and semantic memory (small effect size: r = 0.16; k = 23). Similarly, the olfactory detection threshold was associated with both episodic (small to medium effect size: r = 0.25; k = 5) and semantic memory (small effect size: r = 0.17; k = 7). Age was found to moderate the relationship between olfactory detection threshold and memory performance. Both olfactory identification and detection threshold performances are associated with declarative memory in older adults, and age only moderates the relationship between olfactory detection threshold and declarative memory performances.

(1) Background: It is well established that the insula is involved in olfaction, though its specific role in olfactory processing remains uncertain. In this paper, we first review the current literature on the insula and olfaction. Then, we describe the case of a 56-year-old man with a left insular cavernoma that caused olfactory disturbances. (2) Results: Structural neuroimaging studies suggest that insular gray matter volume is related to olfactory function, and functional neuroimaging shows that various types of stimuli lead to either lateralized or bilateral insular activations. Studies using electro-cortical stimulation reveal a specific region of the insular cortex, around the central insular sulcus, that could be related to unpleasant odor processing. Previous cases of insular lesions leading to olfactory disturbances suggest that left-sided insular lesions may more frequently lead to olfactory changes. In our patient with a left insular cavernoma, odors that were previously perceived as pleasant started smelling unpleasant and were hard to distinguish. Despite these subjective complaints, olfactory function assessed with the Sniffin’ Sticks test was normal. (3) Conclusions: Current tests may not be sensitive to all types of olfactory impairments associated with insular damage, and further studies should be conducted to develop olfactory tests assessing the hedonic appreciation of odors.

Recent studies have shown the efficacy of a home test for the self-evaluation of olfactory and gustatory functions in quarantined coronavirus disease-2019 (COVID-19) patients. However, testing was often limited to COVID-19 participants, and the accuracy of home test kits was rarely compared to standardized testing. This study aims at providing proof of concept for the validation of the new Chemosensory Perception Test (CPT) developed to remotely assess orthonasal olfactory, retronasal olfactory, and gustatory functions in various populations using common North American household items. In the 2 experiments, a total of 121 participants irrespective of having olfactory and/or gustatory complaints from various causes (COVID-19, sinunasal, post-viral, idiopathic) were tested first, with one or many of the following tests: (i) a brief chemosensory questionnaire, (ii) an olfactory test—Sniffin’ Sticks Test (SST) or University of Pennsylvania Smell Identification Test (UPSIT), and/or (iii) a gustatory test—Brief Waterless Empirical Taste Test (B-WETT). We then applied the CPT which yielded 3 different subscores, namely orthonasal, retronasal, and gustatory CPT scores. The orthonasal CPT score was significantly correlated with SST (ρ = 0.837, P < 0.001) and UPSIT (ρ = 0.364, P < 0.001) scores, and exhibited an excellent accuracy to identify olfactory dysfunction (OD) as compared to SST (area under the curve [AUC]: 0.923 [95% confidence interval {CI}, 0.822–1.000], P < 0.001). The retronasal CPT score but not the gustatory CPT score allowed to distinguish between participants with or without subjective gustatory complaint (AUC: 0.818 [95% CI, 0.726–0.909], P < 0.001). The CPT has the ability to identify OD and to quantify subjective gustatory complaints.

Subjective cognitive decline (SCD) refers to a condition in which older adults are concerned that they are experiencing a decline in cognitive function. The risk of developing Alzheimer's disease (AD) is significantly higher in older adults with SCD, as a proportion of them will go on to develop the disease over the years. Despite overall normal function on cognitive tests, evidence suggests that some SCD individuals may have circumscribed deficits in specific cognitive domains or tests. This study aimed to investigate semantic function in SCD, specifically by comparing the performance of SCD progressors (SCDp) - who fulfilled MCI criteria at follow-up, and SCD non-progressors (SCDnp) - who either remained stable or reverted to normal cognition. The main hypothesis was that the SCDp group would show significantly lower semantic performance than the SCDnp group at baseline. We also expected the SCDp group to decline faster on semantic tests at the two-year follow-up assessment than SCDnp. Data from the CIMA-Q cohort were analyzed. The SCDp and SCDnp groups were formed by precisely matching 25 participants from each group based on age and education levels. Both groups were compared in terms of neuropsychological performance at baseline and follow-up. Independent samples t-tests or ANCOVAs were used to measure baseline performance in the semantic domain and other cognitive domains. To study longitudinal changes in cognitive performance at follow-up, two-factor ANOVAs were performed. At baseline, SCDp participants performed significantly worse than SCDnp participants on the Category (semantic) fluency test, although this difference was not maintained at follow-up. No difference was found in other cognitive domains at baseline. Longitudinal analyses showed that a significant decline in MoCA score was observed in the SCDp group only. The results of this study suggest that reduced verbal semantic fluency in older people with SCD may indicate a higher risk of future cognitive decline.