Abstract Olfaction has privileged access to limbic and memory-related brain regions, yet how ambient odor valence influences memory for emotional faces remains poorly understood. This study examined the effects of pleasant odor, unpleasant odor, and odorless condition on recognition accuracy, reaction time, and directed forgetting of emotional faces. In Experiment 1 (study-recognition, n = 31), unpleasant odor significantly impaired recognition accuracy relative to pleasant odor and odorless condition (ps < .01) and slowed reaction times (p < .01); negative faces were recognized more accurately than positive faces (p < .01). In Experiment 2 (item-method directed forgetting, n = 33), a three-way interaction (p < .05) showed that odor valence selectively modulated directed forgetting depending on face type. Under pleasant odor, positive faces showed a robust directed forgetting effect (p < .01), whereas neutral faces exhibited a marginally reversed effect (p = .052). Under unpleasant odor, neutral faces demonstrated a significant directed forgetting effect (p < .01). No directed forgetting was observed for negative faces across all odor conditions. These findings provide novel behavioral evidence that olfactory contexts do not simply enhance or impair memory globally but selectively tune intentional forgetting in a valence-specific manner, advancing our understanding of how chemosensory environments shape cognitive control over socially relevant emotional information.
In line with the critical role of human olfaction in motivated behavior, positively valenced odors have been shown to boost hedonic perception of visual stimuli, especially facial expressions, compared to unpleasant smells. However, it remains unclear whether pleasant fragrances, which vary in character and subjective affective profile, differentially impact different categories of visual stimuli. We also postulate that individual differences in emotional responses to odors modulate their subsequent effect on hedonic evaluations of images. The current study investigated how (relative to a clean air control) 4 pleasant odors (vanilla, rose, lavender, and lemon) influenced hedonic ratings of different categories of visual images (faces, landscapes, and objects), with each category comprising images of neutral and positive valence. Forty participants (aged 18 to 35) rated the pleasantness of each image during each odor condition presented using a computer-controlled olfactometer. Participants also reported their emotional response to each fragrance on 7 dimensions (happiness, disgust, relaxation, thirstiness, sensuality, energy, and nostalgia) using the Liverpool Emotion and Odor Scale (LEOS), self-report questionnaire. Pleasant odors significantly affected image pleasantness ratings, but the effects of specific fragrances differed by image category. Individual differences in emotional experiences elicited by each fragrance were shown to modulate the impact of odors on hedonic evaluations, and these effects varies across the different image categories. The findings offer new insights into the differential effects of pleasant odors on hedonic evaluations of visual stimuli and the role of individual affective processing in cross-modal olfactory-visual integration.
Taste modulation induced by interactions among specific compounds remains poorly understood. L-histidine and creatinine are both bitter compounds abundant in dried bonito dashi. This study investigated whether 10 bitter compounds could shift the taste quality of L-histidine from bitterness toward sweetness, as assessed by sensory evaluation using a fixed-sum method. When presented alone, 4% L-histidine elicited bitterness accompanied by weak sweetness, whereas iso-bitter creatinine evoked predominantly bitterness. Remarkably, pre-stimulation with creatinine shifted the taste quality of L-histidine toward sweetness. Similar effects were observed after pre-stimulation with isoleucine, tryptophan, phenylalanine, and creatine, but not with histidine, valine, leucine, caffeine, or carnosine. This effect was transient, as increasing the interval after creatinine pre-stimulation restored the bitterness of L-histidine. In addition, 0.1% NaCl altered the bitterness-to-sweetness balance of L-histidine toward sweetness after pre-stimulation with creatinine. The taste quality of histidine alone was highly sensitive to pH: bitterness peaked at pH 7.0, whereas sweetness increased under alkaline conditions. In contrast, varying the pH of the pre-stimulation solution between 5.0 and 8.0 did not affect the modulation of L-histidine taste. These findings demonstrate a previously unrecognized histidine-specific form of taste modulation, suggesting interactions among naturally coexisting bitter compounds may dynamically alter taste qualities in traditional broths and other complex foods.
Sodium ascorbate (AsA-Na) is widely used as a source of vitamin C. However, the mechanisms regulating voluntary intake across different concentrations and nutritional states remain poorly understood. Therefore, we examined behavioral and neural responses to AsA-Na in osteogenic disorder Shionogi (ODS) od/od rats, which lack endogenous vitamin C synthesis. Two-bottle choice tests were used to evaluate long-term behavioral responses, and the contribution of epithelial sodium channel (ENaC)-dependent taste signaling was examined using amiloride. In parallel, chorda tympani (CT) nerve responses were recorded with and without amiloride treatment. AsA-Na consistently showed lower preference scores than NaCl across concentrations. At 30 to 100 mM, the preference for AsA-Na was lower than that for NaCl but significantly higher than that for AsA. Lick responses to AsA-Na were comparable to those for NaCl and were enhanced under vitamin C-deficient conditions. Although the 48-h intake of 100 mM AsA-Na remained low under all conditions, the intake of 10 mM AsA-Na increased selectively during the re-intake phase. Notably, amiloride strongly suppressed CT nerve responses to AsA-Na. While amiloride significantly reduced NaCl preference and intake, it had no effect on AsA-Na preference or sustained intake. These results support a dissociation between ENaC-mediated peripheral sensory signaling and long-term ingestive behavior. Although AsA-Na is detected via sodium taste pathways, this sensory input alone cannot account for sustained intake. Instead, intake is likely influenced by post-ingestive mechanisms in a concentration- and state-dependent manner. These findings suggest an important contribution of internal nutritional signals in shaping chemosensory-driven behavior.
Resident stem cells support tissue maintenance in self-renewing adult tissue niches, including the olfactory epithelium, the peripheral organ for smell. In adult mammals, olfactory basal cells support neurogenesis and barrier epithelial maintenance, but whether additional stem cell compartments contribute to olfactory epithelial reconstitution remains unclear. Using lineage tracing, culture models, and single-cell RNA sequencing (scRNA-seq), we demonstrate directly that cells within adult murine submucosal Bowman's glands give rise to olfactory epithelial sustentacular cells, only after severe epithelial lesion. Modeling scRNA-seq data identifies BMP family ligands, expressed by basal stem cells, as potential signals modulating Bowman's gland differentiation. We developed a Bowman's gland culture model, providing an in vitro platform for testing differentiation. Informed by scRNA-seq modeling, treatment of cultures with BMP7/GDF5/GDF11 drove sustentacular cell differentiation. Together, these findings identify Bowman's glands as an injury-responsive facultative stem cell population capable of contributing to olfactory epithelial repair, a process necessary for maintenance of olfactory function.
