The question of a possible link between dream content and memory consolidation remains open. Afte... more 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 4th day, we found that participants with learning-related (n = 16) and pa...
Most everyday experiences are multisensory, and all senses can trigger the conscious re-experienc... more Most everyday experiences are multisensory, and all senses can trigger the conscious re-experience of unique personal events from the past embedded in their specific spatio-temporal context. Yet, little is known about how a cue’s sensory modality influences episodic memory retrieval, 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 presenting a three-room house where boxes delivered odours, musical pieces and pictures of face. At encoding, participants freely, actively and non-explicitly explored unique and rich episodes. At retrieval, participants were presented with modality-specific memory cues and were told to 1) recognize 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 consistently revealed ...
Episodic memory is defined as the conscious retrieval of specific past events. Whether accurate e... more Episodic memory is defined as the conscious retrieval of specific past events. Whether accurate episodic retrieval requires a recollective experience or if a feeling of knowing is suf-ficient remains unresolved. We recently devised an ecological approach to investigate the controlled cued-retrieval of episodes composed of unnamable odors (What) located spa-tially (Where) within a visual context (Which context). By combining the Remember/Know procedure with our laboratory-ecological approach in an original way, the present study demonstrated that the accurate odor-evoked retrieval of complex and multimodal episodes overwhelmingly required conscious recollection. A feeling of knowing, even when associ-ated with a high level of confidence, was not sufficient to generate accurate episodic retrieval. Interestingly, we demonstrated that the recollection of accurate episodic memories was promoted by odor retrieval-cue familiarity and describability. In conclusion, our study suggested that ...
doi: 10.3389/fncir.2015.00049 The olfactory thalamus: unanswered questions about the role of the ... more doi: 10.3389/fncir.2015.00049 The olfactory thalamus: unanswered questions about the role of the mediodorsal thalamic nucleus in olfaction
Previous studies have shown activation of right orbitofrontal cortex during judgments of odor fam... more Previous studies have shown activation of right orbitofrontal cortex during judgments of odor familiarity. In the present study, we sought to extend our knowledge about neural circuits involved in such a task. Fourteen right-handed male subjects were tested in fMRI in a single functional run of two olfactory conditions (detection and familiarity judgment). Within each condition, three epochs were performed. During the familiarity condition, subjects rated whether odors were familiar or unfamiliar, whereas during the detection condition, participants decided whether the odor was present or not. Contrasting familiarity with detection conditions, odor-activated areas were found mainly including the piriform cortex (PC), and hippocampus in the right hemisphere, and the inferior frontal gyrus and amygdala in the left hemisphere. Right PC activation was functionally connected with right hippocampus and left PC during that same task. By showing that PC was activated during a familiarity ju...
Background: Reliable evaluation of patients with unresponsive wakefulness syndrome (UWS) or in a ... more Background: Reliable evaluation of patients with unresponsive wakefulness syndrome (UWS) or in a minimally conscious state (MCS) remains a major challenge. It has been suggested that the expression of residual cerebral function could be improved by allowing patients to listen to their favourite music. However, the potential effect of music on behavioural responsiveness, as well as the effect of preferred stimuli in other sensory modalities (e.g. olfaction), remain poorly understood. Objective: The aim of our study was to investigate the effect of sensory modality (auditory versus olfactory) and preference (preferred versus neutral) of the test stimuli on patients' subsequent performance on the Coma Recovery Scale-Revised (CRS-R). Research design: Within-subject design because of inter-individual differences between patients. Methods and procedures: We studied four items from the CRS-R (visual pursuit using a mirror, auditory localization of the own name and two movements to command) in 13 patients (7 MCS; 6 UWS). Main outcomes and results: Auditory stimuli triggered higher responsiveness compared to olfactory stimuli, and preferred stimuli were followed by higher scores than did neutral stimuli. Conclusions: Findings suggest that preferred auditory stimuli at the bedside contribute to the expression of residual function and could improve the diagnostic assessment.
Cerebral imaging and olfactory disorders: a review. Olfactory disorders are often misjudged and r... more Cerebral imaging and olfactory disorders: a review. Olfactory disorders are often misjudged and rarely given due clinical consideration. Nevertheless, they occur in a wide range of neurological disorders, and their evaluation can help in diagnosis. Whereas psychophysical tests have been used to evaluate olfactory dysfunction in numerous diseases, functional brain imaging using olfactory stimuli is an emergent technique and few studies have been published to date. After a reminder of cerebral imaging and analysis techniques and a rapid description of our actual knowledge of olfactory processes in healthy subjects, the current review focuses on cerebral imaging studies performed on patients with neurological disorders and presenting olfactory dysfunction. Neurological disorders such as Alzheimer's disease, Parkinson's disease, epilepsy, migraine, multiple chemical sensitivity and schizophrenia are examined.
From these two experimental conditions, four response categories can be defined: true memory (cor... more From these two experimental conditions, four response categories can be defined: true memory (correct recognition, Hit) and Miss when the old items are respectively accurately recognized and incorrectly rejected, and correct rejection (CR) and false recognition (false alarm, FA) when the new items are respectively correctly rejected and incorrectly recognized. In the framework of the signaldetection theory, a memory score reflects the subject's ability to discriminate between old and new items, and a response bias score reflects the decision rule adopted when responding (Lockhart and Murdock, 1970; Snodgrass and Corwin, 1988). One can further hypothesize that Hit responses rely more on a recollection process, while FAs rely more on a familiarity process (Yonelinas et al., 1996; Wixted and Stretch, 2004).
Odors are powerful cues that trigger episodic memories. However, in light of the amount of behavi... more Odors are powerful cues that trigger episodic memories. However, in light of the amount of behavioral data describing the characteristics of episodic odor memory, the paucity of information available on the neural substrates of this function is startling. Furthermore, the diversity of experimental paradigms complicates the identification of a generic episodic odor memory network. We conduct a systematic review of the literature depicting the current state of the neural correlates of episodic odor memory in healthy humans by placing a focus on the experimental approaches. Functional neuroimaging data are introduced by a brief characterization of the memory processes investigated. We present and discuss laboratory-based approaches, such as odor recognition and odor associative memory, and autobiographical approaches, such as the evaluation of odor familiarity and odor-evoked autobiographical memory. We then suggest the development of new laboratory-ecological approaches allowing for the controlled encoding and retrieval of specific multidimensional events that could open up new prospects for the comprehension of episodic odor memory and its neural underpinnings. While large conceptual differences distinguish experimental approaches, the overview of the functional neuroimaging findings suggests relatively stable neural correlates of episodic odor memory.
leads to a propositional representation of the inferred state of disgust. This representation the... more leads to a propositional representation of the inferred state of disgust. This representation then determines our decision not to eat the food. Another interpretation of the phenomenon may be based on a "sensory motor resonance" hypothesis. Observing the facial expression
What neural mechanism underlies the capacity to understand the emotions of others? Does this mech... more What neural mechanism underlies the capacity to understand the emotions of others? Does this mechanism involve brain areas normally involved in experiencing the same emotion? We performed an fMRI study in which participants inhaled odorants producing a strong feeling of disgust. The same participants observed video clips showing the emotional facial expression of disgust. Observing such faces and feeling disgust
Olfactory processes were reported to be lateralized. The purpose of this study was to further exp... more Olfactory processes were reported to be lateralized. The purpose of this study was to further explore this phenomenon and investigate the effect of the hemispheric localization of epileptogenic foci on olfactory deficits in patients with temporal lobe epilepsy (TLE). Olfactory functioning was assessed in 61 patients and 60 healthy control (HC) subjects. The patients and HC subjects were asked to rate the intensity, pleasantness, familiarity, and edibility of 12 common odorants and then identify them. Stimulations were delivered monorhinally in the nostril ipsilateral to the epileptogenic focus in TLE and arbitrarily in either the left or the right nostril in the HC subjects. The results demonstrated that regardless of the side of stimulation, patients with TLE had reduced performance in all olfactory tasks compared with the HC subjects. With regard to the side of the epileptogenic focus, patients with left TLE judged odors as less pleasant and had more difficulty with identification than patients with right TLE, underlining a privileged role of the left hemisphere in the emotional and semantic processing of odors. Finally, irrespective of group, a tendency towards a right-nostril advantage for judging odor familiarity was found in agreement with a prominent role of the right hemisphere in odor memory processing.
We behaviorally explore the link between olfaction, emotion and memory by testing the hypothesis ... more We behaviorally explore the link between olfaction, emotion and memory by testing the hypothesis that the emotion carried by odors facilitates the memory of specific unique events. To investigate this idea, we used a novel behavioral approach inspired by a paradigm developed by our team to study episodic memory in a controlled and as ecological as possible way in humans. The participants freely explored three unique and rich laboratory episodes; each episode consisted of three unfamiliar odors (What) positioned at three specific locations (Where) within a visual context (Which context). During the retrieval test, which occurred 24-72 h after the encoding, odors were used to trigger the retrieval of the complex episodes. The participants were proficient in recognizing the target odors among distractors and retrieving the visuospatial context in which they were encountered. The episodic nature of the task generated high and stable memory performances, which were accompanied by faster responses and slower and deeper breathing. Successful odor recognition and episodic memory were not related to differences in odor investigation at encoding. However, memory performances were influenced by the emotional content of the odors, regardless of odor valence, with both pleasant and unpleasant odors generating higher recognition and episodic retrieval than neutral odors. Finally, the present study also suggested that when the binding between the odors and the spatio-contextual features of the episode was successful, the odor recognition and the episodic retrieval collapsed into a unique memory process that began as soon as the participants smelled the odors.
Previous positron emission tomography studies of right-handed individuals show that the left orbi... more Previous positron emission tomography studies of right-handed individuals show that the left orbitofrontal cortex is dominant during emotional processing of odors. We collected functional magnetic resonance imaging data from 28 subjects to study this network as a function of odor hedonic valence (pleasant vs. unpleasant), active hedonic judgments versus passive sensation of hedonically charged odors, handedness, and gender. Two functional runs were performed, with pleasant and unpleasant odors presented in different epochs. In the first run, subjects passively smelled odorants, whereas in the second run they rated degree of odor pleasantness or unpleasantness by using a "finger-span" technique that simulated a visual rating scale. Electrodermal and plethysmography responses were simultaneously recorded to control for covert, physiological manifestations of the emotional response. The piriform-amygdala area and ventral insula were activated more for unpleasant than pleasant odors. More extreme ratings were also associated with higher electrodermal amplitude, suggesting that activation stemmed more from emotional or hedonic intensity than valence, and that unpleasant odors induced more arousal than pleasant odors. Unpleasant odors activated the left ventral insula in right-handers and the right ventral insula in left-handers, suggesting lateralized processing of emotional odors as a function of handedness. Active decisions about odor pleasantness induced specific left orbitofrontal cortex activation, implicating the role of this area in the conscious assessment of the emotional quality of odors. Finally, left orbitofrontal cortex was more active in women than men, potentially in relation to women's well-documented advantage in odor identification.
The human brain's ability to adapt to environmental changes is obvious in specific sensory domain... more The human brain's ability to adapt to environmental changes is obvious in specific sensory domains of experts, and olfaction is one of the least investigated senses. As we have previously demonstrated that olfactory expertise is related to functional brain modifications, we investigated here whether olfactory expertise is also coupled with structural changes. We used voxel-based morphometry to compare the gray-matter volume in student and professional perfumers, as well as untrained control subjects, and accounted for all methodological improvements that have been recently developed to limit possible errors associated with image processing. In all perfumers, we detected an increase in gray-matter volume in the bilateral gyrus rectus/medial orbital gyrus (GR/MOG), an orbitofrontal area that surrounds the olfactory sulcus. In addition, gray-matter volume in the anterior PC and left GR/MOG was positively correlated with experience in professional perfumers. We concluded that the acute olfactory knowledge acquired through extensive olfactory training leads to the structural reorganization of olfactory brain areas.
Previous studies have shown activation of right orbitofrontal cortex during judgments of odor fam... more Previous studies have shown activation of right orbitofrontal cortex during judgments of odor familiarity. In the present study, we sought to extend our knowledge about neural circuits involved in such a task. Fourteen right-handed male subjects were tested in fMRI in a single functional run of two olfactory conditions (detection and familiarity judgment). Within each condition, three epochs were performed. During the familiarity condition, subjects rated whether odors were familiar or unfamiliar, whereas during the detection condition, participants decided whether the odor was present or not. Contrasting familiarity with detection conditions, odor-activated areas were found mainly including the piriform cortex (PC), and hippocampus in the right hemisphere, and the inferior frontal gyrus and amygdala in the left hemisphere. Right PC activation was functionally connected with right hippocampus and left PC during that same task. By showing that PC was activated during a familiarity judgment task, the present study gives supports to the notion that PC participates in the processing of odor memory. It further showed preferential involvement of the right hemisphere in familiarity judgments.
Episodic memory is defined as the conscious recollection of a personal event (What) in its spatia... more Episodic memory is defined as the conscious recollection of a personal event (What) in its spatial (Where) and contextual (Which context) environment. In existing approaches, human episodic memory is either explored separately from real-life situations or is not fully controlled. In this study, we propose an intermediate approach, inspired by animal studies, that permits the control of the encoding and recall phases, while still being ecologically valid. As odors are known to be especially evocative reminders, we explored the memory of olfactory episodes. During trial-unique encoding, participants freely explored three episodes, one episode per day, each composed of three unnamable odors (What) that were positioned at specific locations on a board (Where) within a visual context (Which context). On the fourth day, both old and new odors were presented, and when an odor was recognized, the participants had to remember both its spatial location and the visual context in which it occurred. In Experiment 1, the participants were highly proficient at recognizing odors, and they recall the spatio-contextual environment associated with these odors in approximately half of the trials. To adapt the recall procedure to the constraints of fMRI, we conducted Experiment 2 demonstrating that trial repetition did not disturb the memory process. Thus, we first validated our protocol, which investigates the memory of olfactory episodes in a fully controlled way that is as close as possible to real-life situations. Then, we demonstrated the adaptability of our protocol for the future exploration of the neural networks implicated in episodic recall.
Areas of expertise that cultivate specific sensory domains reveal the brain's ability to adapt to... more Areas of expertise that cultivate specific sensory domains reveal the brain's ability to adapt to environmental change. Perfumers are a small population who claim to have a unique ability to generate olfactory mental images. To evaluate the impact of this expertise on the brain regions involved in odor processing, we measured brain activity in novice and experienced (student and professional) perfumers while they smelled or imagined odors. We demonstrate that olfactory imagery activates the primary olfactory (piriform) cortex (PC) in all perfumers, demonstrating that similar neural substrates were activated in odor perception and imagination. In professional perfumers, extensive olfactory practice influences the posterior PC, the orbitofrontal cortex, and the hippocampus; during the creation of mental images of odors, the activity in these areas was negatively correlated with experience. Thus, the perfumers' expertise is associated with a functional reorganization of key olfactory and memory brain regions, explaining their extraordinary ability to imagine odors and create fragrances. Hum Brain Mapp 33:224-234, 2012. V
Discriminating between successively presented odors requires brief storage of the first odor's pe... more Discriminating between successively presented odors requires brief storage of the first odor's perceptual trace, which then needs to be subsequently compared to the second odor in the pair. This study explores the cortical areas involved in odor discrimination and compares them with findings from studies of working-memory, traditionally investigated with n-back paradigms. Sixteen righthanded subjects underwent H 2 15 O positron emission tomography during counterbalanced conditions of odorless sniffing, repeated single odor detection, multiple odor detection, and conscious successive discrimination between odor pairs. Eight odorants were delivered using a computer-controlled olfactometer through a birhinal nasal cannula. Conscious successive odor discrimination evoked significantly greater activity in the left anterior insula and frontopolar gyrus when compared to reported sensory detection of the identical odors. Additional activation was found in the left lateral orbital/inferior frontal and middle frontal gyri when discrimination was compared to the odorless condition. The left anterior insula is likely involved in the evaluation of odor properties. Consistent with other studies, frontopolar and middle frontal gyrus activation is more likely related to working memory during odor discrimination.
The question of a possible link between dream content and memory consolidation remains open. Afte... more 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 4th day, we found that participants with learning-related (n = 16) and pa...
Most everyday experiences are multisensory, and all senses can trigger the conscious re-experienc... more Most everyday experiences are multisensory, and all senses can trigger the conscious re-experience of unique personal events from the past embedded in their specific spatio-temporal context. Yet, little is known about how a cue’s sensory modality influences episodic memory retrieval, 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 presenting a three-room house where boxes delivered odours, musical pieces and pictures of face. At encoding, participants freely, actively and non-explicitly explored unique and rich episodes. At retrieval, participants were presented with modality-specific memory cues and were told to 1) recognize 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 consistently revealed ...
Episodic memory is defined as the conscious retrieval of specific past events. Whether accurate e... more Episodic memory is defined as the conscious retrieval of specific past events. Whether accurate episodic retrieval requires a recollective experience or if a feeling of knowing is suf-ficient remains unresolved. We recently devised an ecological approach to investigate the controlled cued-retrieval of episodes composed of unnamable odors (What) located spa-tially (Where) within a visual context (Which context). By combining the Remember/Know procedure with our laboratory-ecological approach in an original way, the present study demonstrated that the accurate odor-evoked retrieval of complex and multimodal episodes overwhelmingly required conscious recollection. A feeling of knowing, even when associ-ated with a high level of confidence, was not sufficient to generate accurate episodic retrieval. Interestingly, we demonstrated that the recollection of accurate episodic memories was promoted by odor retrieval-cue familiarity and describability. In conclusion, our study suggested that ...
doi: 10.3389/fncir.2015.00049 The olfactory thalamus: unanswered questions about the role of the ... more doi: 10.3389/fncir.2015.00049 The olfactory thalamus: unanswered questions about the role of the mediodorsal thalamic nucleus in olfaction
Previous studies have shown activation of right orbitofrontal cortex during judgments of odor fam... more Previous studies have shown activation of right orbitofrontal cortex during judgments of odor familiarity. In the present study, we sought to extend our knowledge about neural circuits involved in such a task. Fourteen right-handed male subjects were tested in fMRI in a single functional run of two olfactory conditions (detection and familiarity judgment). Within each condition, three epochs were performed. During the familiarity condition, subjects rated whether odors were familiar or unfamiliar, whereas during the detection condition, participants decided whether the odor was present or not. Contrasting familiarity with detection conditions, odor-activated areas were found mainly including the piriform cortex (PC), and hippocampus in the right hemisphere, and the inferior frontal gyrus and amygdala in the left hemisphere. Right PC activation was functionally connected with right hippocampus and left PC during that same task. By showing that PC was activated during a familiarity ju...
Background: Reliable evaluation of patients with unresponsive wakefulness syndrome (UWS) or in a ... more Background: Reliable evaluation of patients with unresponsive wakefulness syndrome (UWS) or in a minimally conscious state (MCS) remains a major challenge. It has been suggested that the expression of residual cerebral function could be improved by allowing patients to listen to their favourite music. However, the potential effect of music on behavioural responsiveness, as well as the effect of preferred stimuli in other sensory modalities (e.g. olfaction), remain poorly understood. Objective: The aim of our study was to investigate the effect of sensory modality (auditory versus olfactory) and preference (preferred versus neutral) of the test stimuli on patients' subsequent performance on the Coma Recovery Scale-Revised (CRS-R). Research design: Within-subject design because of inter-individual differences between patients. Methods and procedures: We studied four items from the CRS-R (visual pursuit using a mirror, auditory localization of the own name and two movements to command) in 13 patients (7 MCS; 6 UWS). Main outcomes and results: Auditory stimuli triggered higher responsiveness compared to olfactory stimuli, and preferred stimuli were followed by higher scores than did neutral stimuli. Conclusions: Findings suggest that preferred auditory stimuli at the bedside contribute to the expression of residual function and could improve the diagnostic assessment.
Cerebral imaging and olfactory disorders: a review. Olfactory disorders are often misjudged and r... more Cerebral imaging and olfactory disorders: a review. Olfactory disorders are often misjudged and rarely given due clinical consideration. Nevertheless, they occur in a wide range of neurological disorders, and their evaluation can help in diagnosis. Whereas psychophysical tests have been used to evaluate olfactory dysfunction in numerous diseases, functional brain imaging using olfactory stimuli is an emergent technique and few studies have been published to date. After a reminder of cerebral imaging and analysis techniques and a rapid description of our actual knowledge of olfactory processes in healthy subjects, the current review focuses on cerebral imaging studies performed on patients with neurological disorders and presenting olfactory dysfunction. Neurological disorders such as Alzheimer's disease, Parkinson's disease, epilepsy, migraine, multiple chemical sensitivity and schizophrenia are examined.
From these two experimental conditions, four response categories can be defined: true memory (cor... more From these two experimental conditions, four response categories can be defined: true memory (correct recognition, Hit) and Miss when the old items are respectively accurately recognized and incorrectly rejected, and correct rejection (CR) and false recognition (false alarm, FA) when the new items are respectively correctly rejected and incorrectly recognized. In the framework of the signaldetection theory, a memory score reflects the subject's ability to discriminate between old and new items, and a response bias score reflects the decision rule adopted when responding (Lockhart and Murdock, 1970; Snodgrass and Corwin, 1988). One can further hypothesize that Hit responses rely more on a recollection process, while FAs rely more on a familiarity process (Yonelinas et al., 1996; Wixted and Stretch, 2004).
Odors are powerful cues that trigger episodic memories. However, in light of the amount of behavi... more Odors are powerful cues that trigger episodic memories. However, in light of the amount of behavioral data describing the characteristics of episodic odor memory, the paucity of information available on the neural substrates of this function is startling. Furthermore, the diversity of experimental paradigms complicates the identification of a generic episodic odor memory network. We conduct a systematic review of the literature depicting the current state of the neural correlates of episodic odor memory in healthy humans by placing a focus on the experimental approaches. Functional neuroimaging data are introduced by a brief characterization of the memory processes investigated. We present and discuss laboratory-based approaches, such as odor recognition and odor associative memory, and autobiographical approaches, such as the evaluation of odor familiarity and odor-evoked autobiographical memory. We then suggest the development of new laboratory-ecological approaches allowing for the controlled encoding and retrieval of specific multidimensional events that could open up new prospects for the comprehension of episodic odor memory and its neural underpinnings. While large conceptual differences distinguish experimental approaches, the overview of the functional neuroimaging findings suggests relatively stable neural correlates of episodic odor memory.
leads to a propositional representation of the inferred state of disgust. This representation the... more leads to a propositional representation of the inferred state of disgust. This representation then determines our decision not to eat the food. Another interpretation of the phenomenon may be based on a "sensory motor resonance" hypothesis. Observing the facial expression
What neural mechanism underlies the capacity to understand the emotions of others? Does this mech... more What neural mechanism underlies the capacity to understand the emotions of others? Does this mechanism involve brain areas normally involved in experiencing the same emotion? We performed an fMRI study in which participants inhaled odorants producing a strong feeling of disgust. The same participants observed video clips showing the emotional facial expression of disgust. Observing such faces and feeling disgust
Olfactory processes were reported to be lateralized. The purpose of this study was to further exp... more Olfactory processes were reported to be lateralized. The purpose of this study was to further explore this phenomenon and investigate the effect of the hemispheric localization of epileptogenic foci on olfactory deficits in patients with temporal lobe epilepsy (TLE). Olfactory functioning was assessed in 61 patients and 60 healthy control (HC) subjects. The patients and HC subjects were asked to rate the intensity, pleasantness, familiarity, and edibility of 12 common odorants and then identify them. Stimulations were delivered monorhinally in the nostril ipsilateral to the epileptogenic focus in TLE and arbitrarily in either the left or the right nostril in the HC subjects. The results demonstrated that regardless of the side of stimulation, patients with TLE had reduced performance in all olfactory tasks compared with the HC subjects. With regard to the side of the epileptogenic focus, patients with left TLE judged odors as less pleasant and had more difficulty with identification than patients with right TLE, underlining a privileged role of the left hemisphere in the emotional and semantic processing of odors. Finally, irrespective of group, a tendency towards a right-nostril advantage for judging odor familiarity was found in agreement with a prominent role of the right hemisphere in odor memory processing.
We behaviorally explore the link between olfaction, emotion and memory by testing the hypothesis ... more We behaviorally explore the link between olfaction, emotion and memory by testing the hypothesis that the emotion carried by odors facilitates the memory of specific unique events. To investigate this idea, we used a novel behavioral approach inspired by a paradigm developed by our team to study episodic memory in a controlled and as ecological as possible way in humans. The participants freely explored three unique and rich laboratory episodes; each episode consisted of three unfamiliar odors (What) positioned at three specific locations (Where) within a visual context (Which context). During the retrieval test, which occurred 24-72 h after the encoding, odors were used to trigger the retrieval of the complex episodes. The participants were proficient in recognizing the target odors among distractors and retrieving the visuospatial context in which they were encountered. The episodic nature of the task generated high and stable memory performances, which were accompanied by faster responses and slower and deeper breathing. Successful odor recognition and episodic memory were not related to differences in odor investigation at encoding. However, memory performances were influenced by the emotional content of the odors, regardless of odor valence, with both pleasant and unpleasant odors generating higher recognition and episodic retrieval than neutral odors. Finally, the present study also suggested that when the binding between the odors and the spatio-contextual features of the episode was successful, the odor recognition and the episodic retrieval collapsed into a unique memory process that began as soon as the participants smelled the odors.
Previous positron emission tomography studies of right-handed individuals show that the left orbi... more Previous positron emission tomography studies of right-handed individuals show that the left orbitofrontal cortex is dominant during emotional processing of odors. We collected functional magnetic resonance imaging data from 28 subjects to study this network as a function of odor hedonic valence (pleasant vs. unpleasant), active hedonic judgments versus passive sensation of hedonically charged odors, handedness, and gender. Two functional runs were performed, with pleasant and unpleasant odors presented in different epochs. In the first run, subjects passively smelled odorants, whereas in the second run they rated degree of odor pleasantness or unpleasantness by using a "finger-span" technique that simulated a visual rating scale. Electrodermal and plethysmography responses were simultaneously recorded to control for covert, physiological manifestations of the emotional response. The piriform-amygdala area and ventral insula were activated more for unpleasant than pleasant odors. More extreme ratings were also associated with higher electrodermal amplitude, suggesting that activation stemmed more from emotional or hedonic intensity than valence, and that unpleasant odors induced more arousal than pleasant odors. Unpleasant odors activated the left ventral insula in right-handers and the right ventral insula in left-handers, suggesting lateralized processing of emotional odors as a function of handedness. Active decisions about odor pleasantness induced specific left orbitofrontal cortex activation, implicating the role of this area in the conscious assessment of the emotional quality of odors. Finally, left orbitofrontal cortex was more active in women than men, potentially in relation to women's well-documented advantage in odor identification.
The human brain's ability to adapt to environmental changes is obvious in specific sensory domain... more The human brain's ability to adapt to environmental changes is obvious in specific sensory domains of experts, and olfaction is one of the least investigated senses. As we have previously demonstrated that olfactory expertise is related to functional brain modifications, we investigated here whether olfactory expertise is also coupled with structural changes. We used voxel-based morphometry to compare the gray-matter volume in student and professional perfumers, as well as untrained control subjects, and accounted for all methodological improvements that have been recently developed to limit possible errors associated with image processing. In all perfumers, we detected an increase in gray-matter volume in the bilateral gyrus rectus/medial orbital gyrus (GR/MOG), an orbitofrontal area that surrounds the olfactory sulcus. In addition, gray-matter volume in the anterior PC and left GR/MOG was positively correlated with experience in professional perfumers. We concluded that the acute olfactory knowledge acquired through extensive olfactory training leads to the structural reorganization of olfactory brain areas.
Previous studies have shown activation of right orbitofrontal cortex during judgments of odor fam... more Previous studies have shown activation of right orbitofrontal cortex during judgments of odor familiarity. In the present study, we sought to extend our knowledge about neural circuits involved in such a task. Fourteen right-handed male subjects were tested in fMRI in a single functional run of two olfactory conditions (detection and familiarity judgment). Within each condition, three epochs were performed. During the familiarity condition, subjects rated whether odors were familiar or unfamiliar, whereas during the detection condition, participants decided whether the odor was present or not. Contrasting familiarity with detection conditions, odor-activated areas were found mainly including the piriform cortex (PC), and hippocampus in the right hemisphere, and the inferior frontal gyrus and amygdala in the left hemisphere. Right PC activation was functionally connected with right hippocampus and left PC during that same task. By showing that PC was activated during a familiarity judgment task, the present study gives supports to the notion that PC participates in the processing of odor memory. It further showed preferential involvement of the right hemisphere in familiarity judgments.
Episodic memory is defined as the conscious recollection of a personal event (What) in its spatia... more Episodic memory is defined as the conscious recollection of a personal event (What) in its spatial (Where) and contextual (Which context) environment. In existing approaches, human episodic memory is either explored separately from real-life situations or is not fully controlled. In this study, we propose an intermediate approach, inspired by animal studies, that permits the control of the encoding and recall phases, while still being ecologically valid. As odors are known to be especially evocative reminders, we explored the memory of olfactory episodes. During trial-unique encoding, participants freely explored three episodes, one episode per day, each composed of three unnamable odors (What) that were positioned at specific locations on a board (Where) within a visual context (Which context). On the fourth day, both old and new odors were presented, and when an odor was recognized, the participants had to remember both its spatial location and the visual context in which it occurred. In Experiment 1, the participants were highly proficient at recognizing odors, and they recall the spatio-contextual environment associated with these odors in approximately half of the trials. To adapt the recall procedure to the constraints of fMRI, we conducted Experiment 2 demonstrating that trial repetition did not disturb the memory process. Thus, we first validated our protocol, which investigates the memory of olfactory episodes in a fully controlled way that is as close as possible to real-life situations. Then, we demonstrated the adaptability of our protocol for the future exploration of the neural networks implicated in episodic recall.
Areas of expertise that cultivate specific sensory domains reveal the brain's ability to adapt to... more Areas of expertise that cultivate specific sensory domains reveal the brain's ability to adapt to environmental change. Perfumers are a small population who claim to have a unique ability to generate olfactory mental images. To evaluate the impact of this expertise on the brain regions involved in odor processing, we measured brain activity in novice and experienced (student and professional) perfumers while they smelled or imagined odors. We demonstrate that olfactory imagery activates the primary olfactory (piriform) cortex (PC) in all perfumers, demonstrating that similar neural substrates were activated in odor perception and imagination. In professional perfumers, extensive olfactory practice influences the posterior PC, the orbitofrontal cortex, and the hippocampus; during the creation of mental images of odors, the activity in these areas was negatively correlated with experience. Thus, the perfumers' expertise is associated with a functional reorganization of key olfactory and memory brain regions, explaining their extraordinary ability to imagine odors and create fragrances. Hum Brain Mapp 33:224-234, 2012. V
Discriminating between successively presented odors requires brief storage of the first odor's pe... more Discriminating between successively presented odors requires brief storage of the first odor's perceptual trace, which then needs to be subsequently compared to the second odor in the pair. This study explores the cortical areas involved in odor discrimination and compares them with findings from studies of working-memory, traditionally investigated with n-back paradigms. Sixteen righthanded subjects underwent H 2 15 O positron emission tomography during counterbalanced conditions of odorless sniffing, repeated single odor detection, multiple odor detection, and conscious successive discrimination between odor pairs. Eight odorants were delivered using a computer-controlled olfactometer through a birhinal nasal cannula. Conscious successive odor discrimination evoked significantly greater activity in the left anterior insula and frontopolar gyrus when compared to reported sensory detection of the identical odors. Additional activation was found in the left lateral orbital/inferior frontal and middle frontal gyri when discrimination was compared to the odorless condition. The left anterior insula is likely involved in the evaluation of odor properties. Consistent with other studies, frontopolar and middle frontal gyrus activation is more likely related to working memory during odor discrimination.
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Papers by Jane Plailly