Sleep Supports Memory of Odors in Adults but Not in Children

Influence of odor environments on cognitive efficiency: A comprehensive review

Cognitive efficiency, characterized by the rapid and accurate processing of information, significantly enhances work and learning outcomes. This efficiency manifests in improved time management, decision-making, learning capabilities, and creativity. While the influence of thermal, acoustic, and lighting conditions on cognitive performance has been extensively studied, the role of olfactory stimuli remains underexplored. Olfactory perception, distinguished by its intensity, speed of perception, and the breadth of stimuli, plays a pivotal role in cognitive efficiency. This review investigates the mechanisms through which odor environments influence cognitive performance. We analyze how odor environments can affect cognitive efficiency through two different scenarios (work and sleep) and pathways (direct and indirect effects). Current research, which mainly focuses on the interplay between odors, emotional responses, and cognitive efficiency through both subjective and objective measures, is thoroughly analyzed. We highlight existing research gaps and suggest future directions for investigating the influence of odor environments on cognitive efficiency. This review aims to establish a theoretical basis for managing and leveraging odor environments in workplace settings.

Illustrations of interactions needed when investigating sleep using a type of AM-PM PM-AM design

Sleep has long been thought of and promoted to be beneficial for memory. Some claims that sleep aids memory have been made in the absence of a critical interaction. This condition is necessary when using a commonly-used experimental design (a type of AM-PM PM-AM design). We propose that a sleep effect exists only if there is an interaction between groups (experimental and time-of-day controls) and the time of test or study (morning and evening). We show different patterns of results that would and would not support a sleep effect with empirical and model-generated data from recognition memory experiments and hypothetical data. While we use these data to make our point, our suggestions apply to any memory and non-memory-related investigation (e.g., emotional memory, false memory susceptibility, language learning, problem-solving). Testing for and finding the proper interaction will add to the evidence that sleep boosts performance.

Reciprocal relationships between sleep and smell

Despite major anatomical differences with other mammalian sensory systems, olfaction shares with those systems a modulation by sleep/wake states. Sleep modulates odor sensitivity and serves as an important regulator of both perceptual and associative odor memory. In addition, however, olfaction also has an important modulatory impact on sleep. Odors can affect the latency to sleep onset, as well as the quality and duration of sleep. Olfactory modulation of sleep may be mediated by direct synaptic interaction between the olfactory system and sleep control nuclei, and/or indirectly through odor modulation of arousal and respiration. This reciprocal interaction between sleep and olfaction presents novel opportunities for sleep related modulation of memory and perception, as well as development of non-pharmacological olfactory treatments of simple sleep disorders.

Sleep Fosters Odor Recognition in Children with Attention Deficit Hyperactivity Disorder but Not in Typically Developing Children

Prior experience represents a prerequisite for memory consolidation across various memory systems. In the context of olfaction, sleep was found to enhance the consolidation of odors in adults but not in typically developing children (TDC), likely due to differences in pre-experience. Interestingly, unmedicated children with attention deficit hyperactivity disorder (ADHD), a neurodevelopmental condition related to dopamine dysfunction, showed lower perceptive thresholds for odors, potentially allowing for more odor experience compared to TDC. We investigated sleep-associated odor memory consolidation in ADHD. Twenty-eight children with ADHD and thirty age-matched TDC participated in an incidental odor recognition task. For the sleep groups (ADHD: n = 14, TDC: n = 15), the encoding of 10 target odorants took place in the evening, and the retention of odorants was tested with 10 target odorants and 10 distractor odorants the next morning. In the wake groups (ADHD: n = 14, TDC: n = 15), the time schedule was reversed. Odor memory consolidation was superior in the ADHD sleep group compared to the TDC sleep and the ADHD wake groups. Intensity and familiarity ratings during encoding were substantially higher in ADHD compared to TDC. Sleep-associated odor memory consolidation in ADHD is superior to TDC. Abundant pre-experience due to lower perceptive thresholds is suggested as a possible explanation. Olfaction might serve as a biomarker in ADHD.

Relationship between depression and olfactory sensory function: a review

Links between olfactory sensory function and effect have been well established. A robust literature exists in both humans and animals showing that disrupting olfaction sensory function can elicit disordered mood state, including serve as a model of depression. Despite this, considerably less is known regarding the directionality and neural basis of this relationship, e.g. whether disruptions in sensory function precede and contribute to altered mood or if altered mood state precipitates changes in olfactory perception. Further, the neural basis of altered olfactory function in depression remains unclear. In conjunction with clinical studies, animal models represent a valuable tool to understand the relationship between altered mood and olfactory sensory function. Here, we review the relevant literature assessing olfactory performance in depression in humans and in rodent models of depressive-like behavioral states. Rodents allow for detailed characterization of alterations in olfactory perception, manipulation of experiential events that elicit depressive-like phenotypes, and allow for interrogation of potential predictive markers of disease and the cellular basis of olfactory impairments associated with depressive-like phenotypes. We synthesize these findings to identify paths forward to investigate and understand the complex interplay between depression and olfactory sensory function.

Incorporation of fragmented visuo-olfactory episodic memory into dreams and its association with memory performance

The question of a possible link between dream content and memory consolidation remains open. After a comprehensive review of the literature, we present novel findings from an experiment testing whether the incorporation of recently learned stimuli into dream reports is associated with improved post-sleep memory performance. Thirty-two high dream recallers freely explored new visuo-olfactory episodes for 3 consecutive days. During the nights following each non-explicit encoding, participants wore a wrist actimeter, and woke up at 5am and their usual waking time to record their dreams (intensity of all oneiric sensory perception was assessed using scales). A total of 120 dreams were reported and elements related to the encoding phase were identified in 37 of them, either learning-related (mainly visual- and rarely olfactory-related elements), or experiment-related (lab- or experimenters-related elements). On the 4^th day, we found that participants with learning-related (n = 16) and participants with learning-related and/or experiment-related dreams (n = 21) had similar odor recognition and odor-evoked episodic memory with the other participants. However, they had significantly better visuo-spatial memory of the episodes in comparison to the other participants. Our results support the hypothesis that the learning phase is loosely incorporated into dreams and that this incorporation is associated with sleep related memory consolidation.

[Sleep and cognition in children and adolescents]

Sleep and cognition in children and adolescents Abstract. In this review, one of the most important functions of sleep was described: Its role in promoting cognitive processes in children and adolescents. Particularly, studies of older children and adolescents revealed that sleep interacts in a complex manner with cognitive performance. Moreover, it was shown that sleep supports long-term memory even in young children. This is true for many different long-term memory systems such as memory of factual information (declarative memory), language acquisition, and for reward-related learning, but less so for learning motor skills. Clinical implications arise from observing the consequences of sleep deficits in children and adolescents due to early school hours or due to clinical conditions like attention deficits hyperactive disorder (ADHD), sleep apnea syndrome or other sleep disturbances. Current research has only partially shown that the treatment of sleep problems also benefits cognitive and memory performance. Filling this gap remains an opportunity for further research.

Sleep and Olfaction among Older Adults

BACKGROUND

Sleep and olfaction are both critical physiological processes that tend to worsen with age. Decline in olfaction can be an early indicator of neurodegenerative diseases, whereas poor sleep quality is associated with reduced physical and mental health. Given associations with aging-related health declines, we explored whether variations in sleep were associated with olfactory function among older adults.

METHODS

We assessed the relationship between sleep characteristics and olfaction among 354 community-dwelling older adults. Olfaction was measured using a validated field and survey research tool. Sleep characteristics were measured using wrist actigraphy and with self-report of sleep problems. We fit structural equation models of latent constructs of olfaction based on olfactory task items and let this be a function of each sleep characteristic.

RESULTS

Actigraph sleep quality measures were associated with odor identification, but not with odor sensitivity. Longer duration sleepers had worse odor sensitivity compared to medium (58 h) sleepers, but sleep duration was not associated with odor identification. Reported sleep problems and reported usual duration were not associated with olfaction.

CONCLUSIONS

Diminished sleep quality was associated with reduced capacity to identify odors. Determining whether this is a causal association will require further study and longitudinal data.