Olfactory LOVER: behavioral and neural correlates of autobiographical odor memory

Using olfactory cues in text materials benefits delayed retention and schemata construction

Olfactory cues are considered a new sensory medium that can enhance learning, but the lack of empirical data has hampered their widespread use in educational practice. This requires empirical research to explore the effects of olfactory cues on learning. To address this research need, an experimental research study was conducted among 87 fourth graders from a Chinese elementary school. It explored the innovative design of adding olfactory cues to text materials by examining their effects on retention and schemata construction as learning outcomes, as well as their influence on learners' cognitive load and learning experience. In this between-subjects design experiment, the experimental group (n = 44) learned text materials with the introduction of olfactory cues, while the control group (n = 43) only learned text materials. After the learning activity, participants were asked to complete the questionnaires, immediate test, and delayed test. The results revealed that the usage of olfactory cues synchronized with text materials can enhance delayed retention, facilitate schemata construction, and improve learner experience without increasing cognitive load. This study confirms the potential of well-designed olfactory cues in educational practice and provides insights for designing and presenting multimedia learning resources.

Episodic memory and recognition are influenced by cues' sensory modality: comparing odours, music and faces using virtual reality

Most everyday experiences are multisensory, and all senses can trigger the conscious re-experience of unique personal events embedded in their specific spatio-temporal context. Yet, little is known about how a cue's sensory modality influences episodic memory, and which step of this process is impacted. This study investigated recognition and episodic memory across olfactory, auditory and visual sensory modalities in a laboratory-ecological task using a non-immersive virtual reality device. At encoding, participants freely and actively explored unique and rich episodes in a three-room house where boxes delivered odours, musical pieces and pictures of face. At retrieval, participants were presented with modality-specific memory cues and were told to 1) recognise encoded cues among distractors and, 2) go to the room and select the box in which they encountered them at encoding. Memory performance and response times revealed that music and faces outperformed odours in recognition memory, but that odours and faces outperformed music in evoking encoding context. Interestingly, correct recognition of music and faces was accompanied by more profound inspirations than correct rejection. By directly comparing memory performance across sensory modalities, our study demonstrated that despite limited recognition, odours are powerful cues to evoke specific episodic memory retrieval.

Exploring Taiwanese Consumer Dietary Preferences for Various Vinegar Condiments: Novel Dietary Patterns across Diverse Cultural Contexts

The use of vinegar as a culinary seasoning in various global cuisines to enhance the taste characteristics and profiles of foods has been extensively documented in the culinary literature. Particularly notable is traditional Taiwanese-style thick soup, where the incorporation of vinegar plays a fundamental role in imparting distinct flavors. In the context of this experimental investigation, the foundational base of Taiwanese-style thick soup serves as the platform for a meticulously planned sensory and dietary behavior evaluation. Our research methodology combines the use of survey questionnaires and experimental techniques, employing purposive sampling and snowball sampling methods to recruit participants. The central focus of this study is to understand consumers' culinary preferences when presented with a choice between two contrasting types of vinegar-specifically, black vinegar and balsamic vinegar-as alternative gastronomic enhancements. This precise orchestration of data collection and systematic evaluation provides a perceptive window into participants' culinary inclinations and food choices, resulting in a detailed and profound understanding of their taste preferences. The empirical findings stemming from this experimentation reveal notably significant differences in the sensory assessments among participants engaging in diverse culinary experiences. Notably, distinct variations are observed in terms of visual perceptions, olfactory distinctions, and overall sensory satisfaction. This study occupies a crucial position within existing research paradigms by strategically expanding the scope of sensory investigations within the realm of Taiwanese-style thick soup. This introduces an innovative aspect represented by the introduction of balsamic vinegar as a compelling alternative to the customary black vinegar. As a result, the emerging findings not only offer compelling insights into the nuanced food choice and taste preferences of consumers, but also open up new and innovative directions within the complex tapestry of Chinese gastronomy.

Elevated Insulin Levels Engage the Salience Network during Multisensory Perception

INTRODUCTION

Brain insulin reactivity has been reported in connection with systematic energy metabolism, enhancement in cognition, olfactory sensitivity, and neuroendocrine circuits. High receptor densities exist in regions important for sensory processing. The main aim of the study was to examine whether intranasal insulin would modulate the activity of areas in charge of olfactory-visual integration.

METHODS

As approach, a placebo-controlled double-blind within crossover design was chosen. The experiments were conducted in a research unit of a university hospital. On separate mornings, twenty-six healthy normal-weight males aged between 19 and 31 years received either 40 IU intranasal insulin or placebo vehicle. Subsequently, they underwent 65 min of functional magnetic resonance imaging whilst performing an odor identification task. Functional brain activations of olfactory, visual, and multisensory integration as well as insulin versus placebo were assessed. Regarding the odor identification task, reaction time, accuracy, pleasantness, and intensity measurements were taken to examine the role of integration and treatment. Blood samples were drawn to control for peripheral hormone concentrations.

RESULTS

Intranasal insulin administration during olfactory-visual stimulation revealed strong bilateral engagement of frontoinsular cortices, anterior cingulate, prefrontal cortex, mediodorsal thalamus, striatal, and hippocampal regions (p ≤ 0.001 familywise error [FWE] corrected). In addition, the integration contrast showed increased activity in left intraparietal sulcus, left inferior frontal gyrus, left superior frontal gyrus, and left middle frontal gyrus (p ≤ 0.013 FWE corrected).

CONCLUSIONS

Intranasal insulin application in lean men led to enhanced activation in multisensory olfactory-visual integration sites and salience hubs which indicates stimuli valuation modulation. This effect can serve as a basis for understanding the connection of intracerebral insulin and olfactory-visual processing.

Odor exposure and recall of a virtual reality crime scene: A preliminary study

Environmental context reinstatement has a particular value for recall of information in forensic interviews. Since odors are valuable memory cues and can act as memory triggers, in our preliminary study we explored whether odor exposure can help people recall details of a crime scene. The study comprised 58 women and 15 men aged 22-35 who immersed in a carefully controlled environment closely resembling an actual crime setting, i.e., a virtual reality crime. Participants were exposed to an odor at encoding, recall, both or neither of these instances, yielding a total of 4 experimental groups that further completed a memory recall task. The crime scene content recall was tested in a free recall and a forced-response test immediately after seeing the crime scene and one month later. We found no significant effects of odor exposure on the free or the cued recall of the crime scene. The memory scores correlated neither with the self-assessed olfactory/visual sensitivity of the subjects, nor with the perceived odor pleasantness. These preliminary findings suggest that introduction of a vanilla odor while encoding and recalling a crime scene does not aid witness recall accuracy.

Olfactory imagery as a retrieval method for autobiographical memories

INTRODUCTION

The retrieval of autobiographical memories is influenced by several factors, such as sensory modality and the emotional salience of memory cues. This study aimed at investigating the interaction between sensory modalities (olfaction, vision) and emotional dimensions (valence, arousal) of imagery cues, on the frequency, quality, and age distribution of the autobiographical memories (AMs) elicited.

METHOD

A total of 296 females (aged between 18 and 35 years) received one out of eight brief instructions for olfactory or visual imagery. The participants were asked to create a mental image with either high arousal/positive valence, high arousal/negative valence, low arousal/positive valence, or low arousal/negative valence (e.g., 'imagine an unpleasant and arousing odor/scene'); no specific stimulus was mentioned in the instruction.

RESULTS

The approach used elicited imagery with autobiographical content in the majority of participants (78%). In terms of frequency, odor imagery, compared to visual imagery, turned out to be more effective at retrieving either unpleasant memories associated with experiences in adulthood, or pleasant childhood memories. In terms of quality, the imagery was rated as less vivid in the olfactory compared to the visual condition (irrespective of valence and arousal of the imagery instruction). Visual imagery was associated with the experience of more diverse emotions (happiness, sadness, anxiety, anger) than odor imagery, which was related primarily with disgust and happiness.

CONCLUSION

Our findings indicate that nonspecific imagery induction is a useful approach in accessing AM.

IMPLICATION

This approach presents promising clinical applications, such as in working with autobiographical memory narratives in psychotherapy.

Development and validation of the Olfactory Memory Test Battery (OMTB) based on odors with high- and low-verbalizability

BACKGROUND

Odor memory is an important field of clinical research for its distinctive characteristics, which differ from those of other sensory systems. To date, several tests have been implemented for the assessment of odor memory. Despite a range of studies demonstrating the importance of verbal mediation in odor memory, few have distinguished odor memory performance in different odor verbalization levels.

NEW METHOD

We aimed to develop a standardized odor memory test toolbox with one group of odors that are easily verbally identified and the other group of odors that are difficult to identify. The test contained two odor categories (high- and low-verbalizability odors), each consisting of three subtests (short- and long-term memory and working memory).

RESULTS

Satisfactory test-retest reliability and solid validity of the odor recognition and working memory test were shown in both odor categories. Moreover, people scored significantly better with high- than low-verbalizability odors. A negative age effect on odor memory performance was also found.

COMPARISON WITH EXISTING METHODS

No previous odor memory test distinguished odor memory performance in different odor verbalization levels, while the Olfactory Memory Test Battery (OMTB) contains high- and low-verbalizability odors and each category has three subtests.

CONCLUSIONS

The present study indicated the OMTB is a comprehensive assessment of odor memory with good reliability and validity. All subtests can be used separately or in combination with each other according to the clinical and research needs.

Influences of age-related positivity effect on characteristics of odor-evoked autobiographical memories in older Japanese adults

Older adults tend to remember past life events more positively than younger adults. This tendency is the age-related positivity effect. The present study examined whether this effect occurred for odor-evoked autobiographical memories. In total, 317 young and 181 older Japanese participants were asked to recall autobiographical events evoked by odors. Participants then completed the odor-evoked autobiographical memory questionnaire (OEAMQ) to measure the characteristics of the recalled memories. In the results, older participants recalled more positive memories than younger participants. Older participants also rated the OEAMQ subscales higher than the younger participants. Furthermore, there were significant positive correlations between the ratings of odor emotional characteristics and OEAMQ subscales. The age-related positivity effect was observed for odor-evoked autobiographical memories. The emotion aroused by odor played a significant role in some attributes of odor-evoked autobiographical memory. The age-related positivity effect in odor-evoked autobiographical memories has important implications for understanding the cognitive mechanisms of aging in autobiographical memory and olfaction and for applications in well-being and dementia in older adults.

Neural suppression in odor recognition memory

Little is known about the neural basis of lower- and higher-order olfactory functions such as odor memory, compared with other sensory systems. The aim of this study was to explore neural networks and correlates associated with 3 functions: passive smelling (PS), odor encoding (OE), and in particular odor recognition memory (ORM). Twenty-six healthy participants were examined using functional magnetic resonance imaging conducted across 3 sessions, one for each function. Independent component analysis revealed a difference between sessions where a distinct ORM component incorporating hippocampus and posterior cingulate showed delayed triggering dissociated from odor stimulation and recognition. By contrasting Hit for ORM (target odors correctly recognized as old) and a combination of PS and detected odors from OE, we found significantly lower activations in amygdala, piriform cortex, insula, thalamus, and the inferior parietal lobule. Region of interest analysis including anterior insula, posterior cingulate gyrus, dentate gyrus, left middle frontal gyrus, amygdala, and piriform cortex demonstrated that Hit were associated with lower activations compared with other memory responses. In summary, our findings suggest that successful recognition of familiar odors (odor familiarity) is associated with neural suppression in the abovementioned regions of interest. Additionally, network including the hippocampus and posterior cingulate is engaged in a postrecognition process. This process may be related to incidental encoding of less familiar and more novel odors (odor novelty) and should be subject for future research.

Intentional and incidental odour-colour binding in working memory

The question of how features are bound together in working memory has become a topic of much research in recent years. However, this is typically focused on visual and/or auditory stimuli. The purpose of this study is to apply established feature binding procedures to investigate odour binding in working memory. Across three experiments, memory for intentionally and incidentally formed odour-colour pairings was tested. Experiment 1 showed that following explicit instruction to remember the odour-colour combinations, young adults can recall lists of 3-pairings at levels above that of chance and exhibit a recency advantage for the last pairing. In Experiment 2 participants were asked to prioritise the first pairing in the list or treat all pairings equally. We observed only limited evidence of prioritisation affecting the serial position function. Experiment 3 explored incidental odour-colour binding. Using a yes/no recognition procedure, accuracy did not differ for positive test probes presented in the same (bound) or different (unbound) colour to encoding. This study is one of the first to examine odour-colour binding in working memory and, taking the evidence together, suggests that odour-colour bindings can be formed in working memory; however, functionality may be limited compared to that of visual feature binding.

Odor-based context-dependent memory: influence of olfactory cues on declarative and nondeclarative memory indices

Reinstating the olfactory learning context can increase access to memory information, but it is not fully clear which memory functions are subject to an enhancing odor context reinstatement effect. Here, we tested whether congruent odor context during encoding and recall positively affected declarative and nondeclarative memory scores using a novel method for manipulation of an odorous environment; namely, intranasal Nosa plugs. Recall of a text and a complex figure as well as performance in a priming task were assessed immediately and 1 wk after encoding. We found that congruent odor exposure at encoding and recall aided free retrieval of a story at delayed testing but had no significant effect on a complex figure recall or a word completion task. Differences between the assessed memory indices suggest that olfactory environmental cues may be primarily efficient in free verbal recall tasks.

A three-factor benefits framework for understanding consumer preference for scented household products: psychological interactions and implications for future development

Humans have deliberately scented their environment for purpose or pleasure for millennia. In the contemporary marketplace most consumers prefer and purchase scented versions of common household products. However, the drivers of this consumer preference have not been elucidated. To explain the attraction to scent in household products we propose a novel three-factor framework, comprising functional benefits (malodor mitigation, base odor coverage, freshening), in-use experience benefits (cleanliness, efficacy, pleasure), and emotional benefits (increasing in confidence, mood and nostalgia). To support this framework, we present new data from a market research survey on US consumer purchasing habits and attitudes towards home cleaning, laundry, and air freshening products. Further substantiating our framework, a focused review of olfactory psychological science illustrating the central role of scent in cognition, wellbeing, motivated behavior, and social behavior, as well as sensory marketing research highlights the benefits and implications of scent in consumer household products. Based on our three-factor framework we go on to discuss the potential for scent to influence health and raise issues to consider (such as potential negative responding to fragranced products). We conclude by showcasing new opportunities for future research in olfactory science and on scented household products that can advance the positive impacts of scent.

ODor-evoked Autobiographical Memory in Alzheimer's disease?

OBJECTIVE

Because memory decline is the hallmark of Alzheimer's disease (AD), an important endeavor for both clinicians and researchers is to improve memory performances in AD. This can be pursued by olfactory stimulation of memory in patients with AD and by studying the effects of olfactory stimulation on autobiographical memory (i.e., memory for personal information). The effects of olfactory stimulation on autobiographical memory in patients with mild AD have been reported by recent research. We thus provide the first comprehensive overview of research on odor-evoked autobiographical memory in AD. We also establish the basis for solid theoretical analysis concerning the memory improvement reported by research on odor-evoked autobiographical memory in AD.

METHOD

We examined literature on odor-evoked autobiographical memories in AD and propose the "OdAMA" (Odor-evoked Autobiographical Memory in Alzheimer's disease) model.

RESULTS AND DISCUSSION

According to OdAMA model, odor exposure activates involuntary access to specific autobiographical memories, which promotes enhanced experience subjective of retrieval in patients with AD and improves their ability to construct not only recent and remote events but also future ones. The OdAMA model could serve as a guide for researchers and clinicians interested in odor-evoked autobiographical memory in AD.

Olfactory Virtual Reality: A New Frontier in the Treatment and Prevention of Posttraumatic Stress Disorder

This perspective piece reviews the clinical condition of posttraumatic stress disorder (PTSD), which is currently increasing due to the COVID-19 pandemic, and recent research illustrating how olfaction is being incorporated into virtual reality (VR) platforms. I then discuss the latest work examining the potential of olfactory virtual reality (OVR) for the treatment of PTSD. From this foundation I suggest novel ways in which OVR may be implemented in PTSD therapy and harnessed for preventing the development of PTSD. Perceptual and chemical features of olfaction that should be considered in OVR applications are also discussed.

Odor is more effective than a visual cue or a verbal cue for the recovery of autobiographical memories in AD

Alzheimer's disease (AD) is associated with an impairment of autobiographical memories, leading to the production of nonspecific memories. Recent research has demonstrated that odor can serve as a powerful cue for the retrieval of autobiographical memories in AD. Moreover, studies conducted in young adults have showed that odor-evoked autobiographical memories are evoked with more details compared with memories triggered by other sensory modalities. Building on the latter research, we compared specificity, subjective experience, emotional characteristics and retrieval time of autobiographical memories evoked by odor cue, visual cue and verbal cue. To this end, we invited participants with mild AD and control participants to retrieve autobiographical memories after the presentation of an odor, a visual representation of the odorant, or a verbal label of the odorant. Results showed more specificity, higher arousal and more positive memories after odor exposure compared to the visual cue and verbal cue in AD and control participants. In AD participants, autobiographical were retrieved faster after odor-exposure compared to memories evoked by a visual cue and a verbal cue, suggesting the automatic nature of odor-evoked autobiographical memories. Overall, these findings demonstrate that odor is more effective than visual or verbal cues for autobiographical retrieval in AD.

The Proust Machine: What a Public Science Event Tells Us About Autobiographical Memory and the Five Senses

Our senses are constantly stimulated in our daily lives but we have only a limited understanding of how they affect our cognitive processes and, especially, our autobiographical memory. Capitalizing on a public science event, we conducted the first empirical study that aimed to compare the relative influence of the five senses on the access, temporal distribution, and phenomenological characteristics of autobiographical memories in a sample of about 400 participants. We found that the access and the phenomenological features of memories varied as a function of the type of sensory cues, but not their temporal distribution. With regard to their influence on autobiographical memory, an overlap between some senses was found, with on one hand, olfaction and taste and, on the other, vision, audition, and touch. We discuss these findings in the light of theories of perception, memory, and the self, and consider methodological implications of the sensory cuing technique in memory research, as well as clinical implications for research in psychopathological and neuropsychological populations.

Sensory Cueing of Autobiographical Memories in Normal Aging and Alzheimer's Disease: A Comparison Between Visual, Auditory, and Olfactory Information

BACKGROUND

Alzheimer's disease (AD) is a chronic, neurodegenerative disease resulting in a progressive decline of autobiographical memories (AMs) which favors the development of psycho-behavioral disorders. One of the most popular psychosocial interventions in dementia care, Reminiscence Therapy, commonly uses sensory cueing to stimulate AMs retrieval. However, few empirical studies have investigated the impact of sensory stimulation on AMs retrieval in AD.

OBJECTIVE

Our goal was to determine the most relevant cue for AMs retrieval in patients with early to mild AD when comparing odors, sounds and pictures.

METHODS

Sixty AD patients, 60 healthy older adults (OA), and 60 healthy young adults (YA) participated in our study. Participants were presented with either 4 odors, 4 sounds, or 4 pictures. For each stimulus, they were asked to retrieve a personal memory, to rate it across 3 dimensions (emotionality, vividness, rarity) and then to date it.

RESULTS

Overall, results showed no clear dominance of one sensory modality over the others in evoking higher-quality AMs. However, they show that using pictures is the better way to stimulate AD patients' AM, as it helps to retrieve a higher number of memories that are also less frequently retrieved, followed by odors. By contrast, auditory cueing with environmental sounds presented no true advantage.

CONCLUSION

Our data should help dementia care professionals to increase the efficiency of Reminiscence Therapy using sensory elicitors. Other clinical implications and future directions are also discussed.

No Evidence That Hormonal Contraceptives Affect Chemosensory Perception

The use of oral contraceptives (OC) in the form of a hormonal pill has been widespread for decades. Despite its popularity and long-time use, there is still much ambiguity and anecdotal reports about a range of potential side effects. Here, we addressed the potential effect of OC use on chemosensory perception. Previous research has almost exclusively focused on olfaction, but we expanded this to the trigeminal system and the sense of taste. We used Bayesian statistics to compare the olfactory, trigeminal, and taste detection abilities between a group of 34 normal cycling women and a group of 26 women using OC. Our results indicated that odor, trigeminal, and taste thresholds were not affected by the use of OC. Moreover, neither odor perception, nor taste perception was affected; all with Bayes factors consistently favoring the null hypothesis. The only exception to these results was odor identification where Bayes factors indicated inconclusive evidence. We conclude that effects of OC use on chemosensory perception are unlikely, and if present, likely are of no to little behavioral relevance.

Could Self-Consciousness Be Enhanced in Alzheimer’s Disease? An Approach from Emotional Sensorial Stimulation

Alzheimer’s disease (AD) provides a valuable field of research into impairment of self-consciousness (SC), because AD patients have a reduced capacity to understand their mental world, to experience and relive previous personal events, as well as to interpret thoughts, feelings, and beliefs about themselves. Several studies observed that AD patients had an altered SC, but not a complete abolition of it. Emotions are an integral part of the construction of personal identity, therefore of Self. In general, most studies on emotion in AD patients have observed that emotion is not completely abolished and it lets them better remember autobiographical events with greater emotional charge. The positive effect of autobiographical memories rich in emotional content, evoked directly/automatically by sensorial stimuli such as familiar odors or music, could be used to reestablish/reinforce the permanence and coherence of the Self in AD. We studied the research of empirical evidence supporting the power of the sensorial cues associated with emotion, which could be capable of enhancing the SC in AD. We presented the studies about “Emotional stimulations” using odor, music, or taste cues in AD. All studies have shown to have a positive impact on SC in AD patients such as odor-evoked autobiographical memories, taste/odor-evoked autobiographical memories, emotional sensorial stimulation using musical cues, and multi-sensorial stimulations using healing gardens. We found research supporting the notion that emotional sensorial stimulations can even temporarily exalt memory, affective state, and personal identity, that is, the SC in AD. The emotional sensory stimulations could be used as a tool to activate the SC in AD and hence improve the quality of life of patients and caregivers.

Effects of Olfactory Stimulation on Past and Future Thinking in Alzheimer’s Disease

Several studies have demonstrated that Alzheimer’s disease (AD) is associated not only with difficulty in remembering past events but also with a compromised ability to imagine future ones. Recent empirical research has also demonstrated that odor is an effective cue to alleviate difficulty in remembering past events in AD. We investigated whether odor exposure would help AD patients to imagine future events. To this end, we invited AD patients and control participants to evoke past and future events after odor exposure or without odor. Analysis showed that AD patients and control participants produced more specific and more emotional past and future events after odor exposure than without odor. However, odor exposure did not improve the retrieval time for future thinking in AD participants. This study is the first to demonstrate positive effects of odor exposure on the ability of AD patients to project themselves into the future.

The reminiscence bump is blind to blindness: Evidence from sound- and odor-evoked autobiographical memory

The reminiscence bump is the disproportionally high reporting of autobiographical memories from adolescence and early adulthood and is typically observed when memories are evoked by cues, such as words, pictures, and sounds. However, when odors are used the bump shifts to early childhood. Although these findings indicate that sensory modality affects the bump, the influence of the individual's sensory function on the reminiscence bumps is unknown. We examined the reminiscence bumps of sound- and odor-evoked autobiographical memories of early blind and sighted individuals, since early blindness implies considerable effects on sensory experience. Despite differences in sensory experience between blind and sighted individuals, the groups displayed similar age distributions of both sound- and odor-evoked memories. The auditory bump spanned the first two decades of life, whereas the olfactory bump was once again found in early childhood. These results demonstrate that the reminiscence bumps are robust to fundamental differences in sensory experience.

Odor-related brain hyper-reactivity in euthymic bipolar disorder: An fMRI and ERP study

Previous studies on olfactory function in patients with bipolar disorder (BD) are limited and contradictory. The current study aimed to comprehensively analyze the olfactory function of patients with euthymic BD using psychophysical, electrophysiological and neuroimaging techniques. Twenty-one patients with BD in remission and 20 healthy controls were tested with the "Sniffin' Sticks" olfactory test. Block-design fMRI data to a pleasant and an unpleasant stimulus were acquired while recording intensity and hedonic ratings. Olfactory event-related potentials (OERP) to the same stimuli were additionally recorded. Results show no differences between patients and healthy controls in terms of self-rated olfactory function and tested olfactory domains (odor threshold, discrimination or identification) (p>0.05). Compared to healthy controls, patients showed an increased fMRI activation in multiple cortical and subcortical regions as a response to olfactory stimulation, as well as larger amplitudes of OERPs regardless of the hedonic valence of the odor. All in all, patients with euthymic BD showed a stronger central responsiveness to odorous stimuli in fMRI and OERPs despite of normal psychophysical results, indicating the probable existence of an odor-related over-reactive brain network in the remission phase of BD.

An in-depth review of the methods, findings, and theories associated with odor-evoked autobiographical memory

Over the past nearly 35 years, there has been sporadic interest in what has commonly come to be known as the Proust phenomenon, whereby autobiographical memories are retrieved and experienced differently when evoked by odors as compared with other types of cues, such as words, images or sounds. The purpose of this review is threefold. First, we provide a detailed analysis of the methods used to investigate Proust effects. Second, we review and analyze the various findings from the literature and determine what we feel to be the most important and stable findings. Third, we provide a series of previously postulated and new hypotheses that attempt to account for the various findings. Given the early stage of research, the current review aims to provide a measure of organization to the field, as well serve as a guide for how future investigations may address the topic. We conclude with the recommendation that research in this area shift its focus from establishing the phenomenon towards explaining its causes.

Emotional and Phenomenological Properties of Odor-Evoked Autobiographical Memories in Alzheimer's Disease

Autobiographical memory, which contains all personal memories relative to our identity, has been found to be impaired in Alzheimer' Disease (AD). Recent research has demonstrated that odor may serve as a powerful cue for the recovery of autobiographical memories in AD. Building on this research, we investigated emotional characteristics (arousal and valence) and subjective reliving of odor-evoked autobiographical memories in AD. We also investigated the relationship between these characteristics and depression. To this end, we invited participants with mild AD and controls to retrieve autobiographical memories after odor exposure or without odor. Results showed higher arousal, subjective reliving and more positive memories after odor exposure compared with the odor-free condition, these differences being observed only in AD participants. We also found that emotion (arousal and valence) and subjective reliving triggered by odor were associated with depressive symptoms in AD. These findings demonstrate that odor may be a useful cue to trigger more detailed, vivid and positive events in AD.

Introduction to the Cognitive Abilities Account for the Reminiscence Bump in the Temporal Distribution of Autobiographical Memory

People tend to recall more specific personal events from adolescence and early adulthood than from other lifetime periods, a finding known as the reminiscence bump. Several explanations have suggested that events from the reminiscence bump are especially emotional, important, or positive, but studies using cue words have not found support for these claims. An alternative account postulates that cognitive abilities function optimally in adolescence and early adulthood, which may cause more memories to be stored in those lifetime periods. Although other studies have previously discussed the cognitive abilities account as a possible explanation for the reminiscence bump, it was only recently shown that cognitive abilities are indeed related to autobiographical memory performance. When this recent finding is combined with previous findings that cognitive abilities as well as autobiographical memory function optimally in adolescence and early adulthood, they suggest that the cognitive abilities account is a promising explanation for the reminiscence bump in the temporal distribution of word-cued memories. However, because the account does not aim to explain the reminiscence bump in the distribution of highly significant events, it should be regarded as complementary to the existing accounts.

From Nose to Memory: The Involuntary Nature of Odor-evoked Autobiographical Memories in Alzheimer's Disease

Research suggests that odors may serve as a potent cue for autobiographical retrieval. We tested this hypothesis in Alzheimer's disease (AD) and investigated whether odor-evoked autobiographical memory is an involuntary process that shares similarities with music-evoked autobiographical memory. Participants with mild AD and controls were asked to retrieve 2 personal memories after odor exposure, after music exposure, and in an odor-and music-free condition. AD participants showed better specificity, emotional experience, mental time travel, and retrieval time after odor and music exposure than in the control condition. Similar beneficial effects of odor and music exposure were observed for autobiographical characteristics (i.e., specificity, emotional experience, and mental time travel), except for retrieval time which was more improved after odor than after music exposure. Interestingly, regression analyses suggested executive involvement in memories evoked in the control condition but not in those evoked after music or odor exposure. These findings suggest the involuntary nature of odor-evoked autobiographical memory in AD. They also suggest that olfactory cuing could serve as a useful and ecologically valid tool to stimulate autobiographical memory, at least in the mild stage of the disease.

Olfactory Context Dependent Memory: Direct Presentation of Odorants

Information is retrieved more effectively when the retrieval occurs in the same context as that in which the information was first encoded. This is termed context dependent memory (CDM). One category of cues that have been shown to effectively produce CDM effects are odors. However, it is unclear what the boundary conditions of these CDM effects are. In particular, given that olfaction has been called an implicit sense, it is possible that odors are only effective mnemonic cues when they are presented in the background. This assertion seems even more likely given that previous research has shown odors to be poor cues during paired associate memory tests, where odors are in the focus of attention as mnemonic cues for other information. In order to determine whether odors are only effective contextual mnemonic cues when presented outside the central focus of an observer, an olfactory CDM experiment was performed in which odorants were presented directly, rather than ambiently. Direct presentation was accomplished with the aid of an olfactometer. The olfactometer not only allows for direct presentation of odorants, but provides other methodological benefits, including the allowance of trial by trial manipulations of odorant presentations and, relatedly, time-specific releases of odorants. The presence of the same odor during both encoding and retrieval enhanced memory performance, regardless of whether the odor was presented ambiently or directly. This finding can serve as a basis for future olfactory CDM research which can utilize the benefits of direct presentation.

Phantom Smells: Prevalence and Correlates in a Population-Based Sample of Older Adults

Loss of olfactory function is common in old age, but evidence regarding qualitative olfactory dysfunction in the general older population is scarce. The current study investigates the prevalence and correlates of phantom smell experiences (phantosmia) in a population-based study (Swedish National Study on Aging and Care in Kungsholmen [SNAC-K]) of Swedish adults (n = 2569) aged between 60 and 90 years. Phantosmia was assessed through a standardized interview and defined as reporting having experienced an odor percept in the absence of any stimuli in the surrounding environment that could emit the odor. The relationships between phantosmia and demographic, genetic, health-related, and behavioral variables were analyzed with hierarchical logistic regression analyses. The overall prevalence of phantom smells was 4.9%, and was associated with female gender, carrying the met allele of the BDNF gene, higher vascular risk burden, and reporting distorted smell sensations (parosmia). Olfactory dysfunction was, however, not related to phantosmia. The most frequently reported phantom smell was smoky/burnt. A novel finding was that some individuals reported phantom smells with an autobiographical connotation. The results from this study indicate that the prevalence of phantosmia in the general older population is not negligible and that some factors that are beneficial for preserved olfactory function, such as female gender and the BDNF met allele, are also associated with the occurrence of phantom smells.

The Role of Odor-Evoked Memory in Psychological and Physiological Health

This article discusses the special features of odor-evoked memory and the current state-of-the-art in odor-evoked memory research to show how these unique experiences may be able to influence and benefit psychological and physiological health. A review of the literature leads to the conclusion that odors that evoke positive autobiographical memories have the potential to increase positive emotions, decrease negative mood states, disrupt cravings, and reduce physiological indices of stress, including systemic markers of inflammation. Olfactory perception factors and individual difference characteristics that would need to be considered in therapeutic applications of odor-evoked-memory are also discussed. This article illustrates how through the experimentally validated mechanisms of odor-associative learning and the privileged neuroanatomical relationship that exists between olfaction and the neural substrates of emotion, odors can be harnessed to induce emotional and physiological responses that can improve human health and wellbeing.

Multimodal retrieval of autobiographical memories: sensory information contributes differently to the recollection of events

Previous studies on autobiographical memory have focused on unimodal retrieval cues (i.e., cues pertaining to one modality). However, from an ecological perspective multimodal cues (i.e., cues pertaining to several modalities) are highly important to investigate. In the present study we investigated age distributions and experiential ratings of autobiographical memories retrieved with unimodal and multimodal cues. Sixty-two participants were randomized to one of four cue-conditions: visual, olfactory, auditory, or multimodal. The results showed that the peak of the distributions depends on the modality of the retrieval cue. The results indicated that multimodal retrieval seemed to be driven by visual and auditory information to a larger extent and to a lesser extent by olfactory information. Finally, no differences were observed in the number of retrieved memories or experiential ratings across the four cue-conditions.