Working memory (WM) processes are assumed to operate on a wide variety of sensory materials, yet WM research rarely extends beyond sight and hearing. In this systematic review, we integrate research from studies that address WM in olfaction, the sense of smell, spanning the last 50 yr (N = 44). We assessed whether 21 proposed benchmarks for WM generalize to olfactory WM. Seven benchmarks generalized to olfaction, whereas 2 failed to generalize. Evidence was insufficient to address the remaining 12 benchmarks (4 had mixed support and 8 were yet unaddressed). We conclude that the available evidence indicates that the sense of smell has a short-term memory system that mostly resembles WM processes in higher senses, although there are exceptions related to how olfactory WM performance is associated with other functions. We argue that researchers studying WM should explicitly consider evidence outside of the audio-visual senses when establishing theoretical frameworks. Further, we point out avenues for future research that may help close the remaining gaps in knowledge on this neglected topic.

Chemosensory sensations are often hard to describe and quantify. Language models may facilitate a systematic understanding of sensory descriptions. We accessed consumer and expert reviews of wine, perfume, and food products (English language; about 68 million words in total) and analyzed their sensory descriptions. Using a novel data-driven method based on natural language data, we compared the three chemosensory vocabularies (wine, perfume, food) with respect to their vocabulary overlap and semantic properties, and explored their semantic spaces. The three vocabularies primarily differ with respect to domain specificity, concreteness, descriptor type preference and degree of gustatory vs. olfactory association. Wine vocabulary primarily distinguishes between white wine and red wine flavors and qualities. Food vocabulary separates drinkable and edible food products and ingredients, on the one hand, and savory and non-savory products, on the other. A salient distinction in all three vocabularies is between concrete and abstract/evaluative terms. Valence also plays a role in the semantic spaces of all three vocabularies, but valence is less prominent here than in general olfactory vocabulary. Our method allows a systematic comparison of sensory descriptors in the three product domains and provides a data-driven approach to derive sensory lexicons that can be applied by sensory scientists.

A persistent belief holds that humans can imagine visual content but not odors. While visual imagery is regarded as recreating a perceptual representation, it is unknown whether olfactory mental imagery shares a perceptual format. Visual imagery studies have demonstrated this perceptual formatting using distance and shape similarity judgments, whereas olfactory studies often use single-odor vividness ratings, complicating the establishment of perceptual formatting for odors. Using odor pair similarity scores from two experiments (odor-based: 8,880 ratings from 37 participants, including 20 women; label-based: 129,472 ratings from 2,023 participants, including 1,164 women), we observed a strong correlation (r =.71) between odor-based and label-based odor pairs. The correlation was unaffected by gender and age and was present in a wide range of self-perceived olfactory functions. Pleasantness similarity was the main determinant of overall similarity for both odor-based (r=−.63) and label-based (r=−.45) odor pairs. We then used a large language model to derive semantic similarity scores for the labels of all odor pairs. Semantic similarity only mediated a small part of the observed correlation, further supporting our conclusions that odor imagery shares a perceptual formatting with vision, that odor percepts may be elicited from verbal labels alone, and that odor pair pleasantness may be a dominant and accessible feature in this regard.

Rejection of food, including fruits and vegetables, is prevalent among children. In adolescents and adults, a link has been observed between food neophobia (the rejection of unfamiliar foods) and olfaction, which plays a key role in food acceptance. However, research on olfaction's role in food acceptance and rejection among children is limited. Utilizing the U-sniff test and the Italian Child Neophobia Scale, this study investigated associations between odor awareness, odor identification, food neophobia, and the acceptance of fruits and vegetables in Swedish children aged 9–12 years (n = 126). A Swedish version of the ChiPSO questionnaire on odor awareness (including subscales for food, social and environmental odors) was developed, and initial validation conducted through back translation, cognitive interviews, and exploratory factor analysis. Fruit and vegetable acceptance was assessed through a questionnaire and a tasting session. Findings indicated that food neophobia was associated with lower fruit and vegetable acceptance (questionnaire ρ = −0.296, p = 0.002; tasting session ρ = −0.273, p = 0.004) but no significant associations observed with odor awareness (ρ = 0.159, p = 0.094) or odor identification performance (ρ = −0.141, p = 0.176). However, odor awareness was negatively associated with vegetable acceptance (ρ = −0.200, p = 0.034), while odor identification performance showed no significant associations (questionnaire ρ = −0.049, p = 0.638; tasting session ρ = −0.101, p = 0.316). A negative association was found between odor identification performance and environmental odor awareness (ρ = −0.269, p = 0.010). This suggests that some children may struggle to identify odors due to emotional reactions and avoidant behaviors, reducing engagement and hindering identification. Further exploration of the relationship between olfaction and children's food acceptance or rejection is encouraged.

Background: Subjective cognitive decline (SCD) is a risk factor for future cognitive impairment and dementia. It is uncertain whether the neurodegeneration of the cholinergic system is already present in SCD individuals. We aimed to review the current evidence about the association between SCD and biomarkers of degeneration in the cholinergic system.

Method: Original articles were extracted from three databases: Pubmed, Web of Sciences, and Scopus, in January 2023. Two researchers screened the studies independently.

Results: A total of 11 research articles were selected. SCD was mostly based on amnestic cognitive complaints. Cholinergic system biomarkers included neuroimaging markers of basal forebrain volume, functional connectivity, transcranial magnetic stimulation, or biofluid. The evidence showed associations between basal forebrain atrophy, poorer connectivity of the cholinergic system, and SCD

Conclusions: Degenerative changes in the cholinergic system can be present in SCD. Subjective complaints may help when identifying individuals with brain changes that are associated with cognitive impairment. These findings may have important implications in targeting individuals that may benefit from cholinergic-target treatments at very early stages of neurodegenerative diseases.

Background

More than a year after recovering from COVID-19, a large proportion of individuals, many of whom work in the healthcare sector, still report olfactory dysfunctions. However, olfactory dysfunction was common already before the COVID-19 pandemic, making it necessary to also consider the existing baseline prevalence of olfactory dysfunction. To establish the adjusted prevalence of COVID-19 related olfactory dysfunction, we assessed smell function in healthcare workers who had contracted COVID‐19 during the first wave of the pandemic using psychophysical testing.

Methods

Participants were continuously tested for SARS‐CoV‐2 IgG antibodies since the beginning of the pandemic. To assess the baseline rate of olfactory dysfunction in the population and to control for the possibility of skewed recruitment of individuals with prior olfactory dysfunction, consistent SARS-CoV‐2 IgG naïve individuals were tested as a control group.

Results

Fifteen months after contracting COVID‐19, 37% of healthcare workers demonstrated a quantitative reduction in their sense of smell, compared to only 20% of the individuals in the control group. Fifty-one percent of COVID‐19‐recovered individuals reported qualitative symptoms, compared to only 5% in the control group. In a follow-up study 2.6 years after COVID-19 diagnosis, 24% of all tested recovered individuals still experienced parosmia.

Conclusions

In summary, 65% of healthcare workers experienced parosmia/hyposmia 15 months after contracting COVID-19. When compared to a control group, the prevalence of olfactory dysfunction in the population increased by 41 percentage points. Parosmia symptoms were still lingering two-and-a half years later in 24% of SARS-CoV-2 infected individuals. Given the amount of time between infection and testing, it is possible that the olfactory problems may not be fully reversible in a plurality of individuals.

Introduction: Disgust sensitivity to body odors plays a role in a set of psychological mechanisms supposedly evolved to avoid pathogens. To assess individual differences in body odor disgust, we previously developed the body odor disgust scale (BODS) and validated it in English. The BODS presents six scenarios where disgust could be evoked by smells coming from an internal source and an external source. The present study aimed to validate the BODS in the Italian population and to find further evidence for its structural, construct, and criterion validity.

Methods: We used two large samples (N = 1,050, F = 527; and N = 402, F = 203, respectively) that were representative of the Italian population for sex and age.

Results: Across these two studies, we confirmed the hypothesized bifactor structure, with all the items loading onto a general body odor disgust sensitivity factor, and on two specific factors related to the internal structure. In terms of construct validity, we found that the BODS converged with pathogen disgust sensitivity of the three-domain disgust scale (TDDS) but was distinct from a general propensity to experience negative emotions. The BODS showed criterion validity in predicting the behavioral intentions toward COVID-19 avoidance behavior, although it did not seem to be incrementally valid when compared to the TDDS pathogen subscale. We also established scalar measurement invariance of the BODS regarding gender and found that women display higher levels of BODS.

Discussion: Results from the Italian version of the BODS indicate its structural, construct, nomological and criterion validity. Furthermore, our result on sex differences in disgust sensitivity are consistent with previous literature, and we discuss them in the broader context of cross-cultural and primate findings that points toward a possible evolutionary explanation of this difference.

Creating and evaluating predictions are considered important features in sensory perception. Little is known about processing differences between the senses and their cortical substrates. Here, we tested the hypothesis that olfaction, the sense of smell, would be highly dependent on (nonolfactory) object-predictive cues and involve distinct cortical processing features. We developed a novel paradigm to compare prediction error processing across senses. Participants listened to spoken word cues (e.g., “lilac”) and determined whether target stimuli (odors or pictures) matched the word cue or not. In two behavioral experiments (total n = 113; 72 female), the disparity between congruent and incongruent response times was exaggerated for olfactory relative to visual targets, indicating a greater dependency on predictive verbal cues to process olfactory targets. A preregistered fMRI study (n = 30; 19 female) revealed the anterior cingulate cortex (a region central for error detection) being more activated by incongruent olfactory targets, indicating a role for olfactory predictive error processing. Additionally, both the primary olfactory and visual cortices were significantly activated for incongruent olfactory targets, suggesting olfactory prediction errors are dependent on cross-sensory processing resources, whereas visual prediction errors are not. We propose that olfaction is characterized by a strong dependency on predictive (nonolfactory) cues and that odors are evaluated in the context of such predictions by a designated transmodal cortical network. Our results indicate differences in how predictive cues are used by different senses in rapid decision-making.

The human brain is organized as a hierarchical global network. Functional connectivity research reveals that sensory cortices are connected to corresponding association cortices via a series of intermediate nodes linked by synchronous neural activity. These sensory pathways and relay stations converge onto central cortical hubs such as the default-mode network (DMN). The DMN regions are believed to be critical for representing concepts and, hence, language acquisition and use. Although prior research has established that major senses are placed at a similar distance from the DMN—five to six connective steps—it is still unknown how the olfactory system functionally connects to the large-scale cortical hubs of the human brain. In this study, we investigated the connective distance from olfactory seed areas to the DMN. The connective distance involves a series of three to four intermediate steps. Furthermore, we parcellated the olfactory cortical subregions and found evidence of two distinct olfactory pathways. One emerges from the anterior olfactory nucleus and olfactory tubercle; it involves early access to the orbitofrontal cortex, known for processing reward and multisensory signals. The other emerges from the frontal and temporal regions of the piriform cortex, involving the anterior insula, intermediate frontal sulcus, and parietal operculum. The results were confirmed in a replication cohort. Our results provide evidence that olfaction has unique early access to the central cortical networks via dual pathways.

Self-reported measures emerge as potential indicators for early detection of dementia and mortality. We investigated the predictive value of different self-reported measures, including subjective cognitive decline (SCD), subjective olfactory impairment (SOI), subjective taste impairment (STI), and self-reported poor health (SPH), in order to determine the risk of progressing to Alzheimer's disease (AD) dementia, Parkinson's disease (PD) dementia, or any-other-cause dementia. A total of 6,028 cognitively unimpaired individuals from the 8th wave of the English Longitudinal Study of Ageing (ELSA) were included as the baseline sample and 5,297 individuals from the 9th wave were included as 2-year follow-up sample. Self-rated measures were assessed using questions from the ELSA structured interview. Three logistic regression models were fitted to predict different the dementia outcomes. SCD based on memory complaints (OR = 11.145; P < 0.001), and older age (OR = 1.108, P < 0.001) significantly predicted the progression to AD dementia at follow-up. SOI (OR = 7.440; P < 0.001) and older age (OR = 1.065, P = 0.035) significantly predicted the progression to PD dementia at follow-up. Furthermore, SCD based on memory complaints (OR = 4.448; P < 0.001) jointly with complaints in other (non-memory) mental abilities (OR = 6.662; P < 0.001), and older age (OR = 1.147, P < 0.001) significantly predicted the progression to dementia of any other cause. Different types of complaints are specifically associated with different dementia outcomes. Our study demonstrates that self-reported measures are a useful and accessible tool when screening for individuals at risk of dementia in the general population.