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Dikeçligil GN, Yang AI, Sanghani N, Lucas T, Chen HI, Davis KA, Gottfried JA. Odor representations from the two nostrils are temporally segregated in human piriform cortex. Curr Biol 2023; 33:5275-5287.e5. [PMID: 37924807 DOI: 10.1016/j.cub.2023.10.021] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2023] [Revised: 10/12/2023] [Accepted: 10/12/2023] [Indexed: 11/06/2023]
Abstract
The human olfactory system has two discrete channels of sensory input, arising from olfactory epithelia housed in the left and right nostrils. Here, we asked whether the primary olfactory cortex (piriform cortex [PC]) encodes odor information arising from the two nostrils as integrated or distinct stimuli. We recorded intracranial electroencephalogram (iEEG) signals directly from PC while human subjects participated in an odor identification task where odors were delivered to the left, right, or both nostrils. We analyzed the time course of odor identity coding using machine-learning approaches and found that uni-nostril odor inputs to the ipsilateral nostril are encoded ∼480-ms faster than odor inputs to the contralateral nostril on average. During naturalistic bi-nostril odor sampling, odor information emerged in two temporally segregated epochs, with the first epoch corresponding to the ipsilateral and the second epoch corresponding to the contralateral odor representations. These findings reveal that PC maintains distinct representations of odor input from each nostril through temporal segregation, highlighting an olfactory coding scheme at the cortical level that can parse odor information across nostrils within the course of a single inhalation.
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Affiliation(s)
- Gülce Nazlı Dikeçligil
- Department of Neurology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
| | - Andrew I Yang
- Department of Neurosurgery, Barrow Neurological Institute, Phoenix, AZ 85013, USA
| | - Nisha Sanghani
- Department of Neurology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Timothy Lucas
- Department of Neurosurgery and Biomedical Engineering, Ohio State University, Columbus, OH 43210, USA
| | - H Isaac Chen
- Department of Neurosurgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Kathryn A Davis
- Department of Neurology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Jay A Gottfried
- Department of Neurology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA; Department of Psychology, School of Arts and Sciences, University of Pennsylvania, Philadelphia, PA 19104, USA
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2
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Dikecligil GN, Yang AI, Sanghani N, Lucas T, Chen HI, Davis KA, Gottfried JA. Odor representations from the two nostrils are temporally segregated in human piriform cortex. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.02.14.528521. [PMID: 36824705 PMCID: PMC9948982 DOI: 10.1101/2023.02.14.528521] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/16/2023]
Abstract
The human olfactory system has two discrete channels of sensory input, arising from olfactory epithelia housed in the left and right nostrils. Here, we asked whether primary olfactory cortex (piriform cortex, PC) encodes odor information arising from the two nostrils as integrated or distinct stimuli. We recorded intracranial EEG signals directly from PC while human subjects participated in an odor identification task where odors were delivered to the left, right, or both nostrils. We analyzed the time-course of odor-identity coding using machine learning approaches, and found that uni-nostril odor inputs to the ipsilateral nostril are encoded ~480 ms faster than odor inputs to the contralateral nostril on average. During naturalistic bi-nostril odor sampling, odor information emerged in two temporally segregated epochs with the first epoch corresponding to the ipsilateral and the second epoch corresponding to the contralateral odor representations. These findings reveal that PC maintains distinct representations of odor input from each nostril through temporal segregation, highlighting an olfactory coding scheme at the cortical level that can parse odor information across nostrils within the course of a single inhalation.
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3
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Tarfa R, Yu SE, Ahmed OH, Moore JA, Bruña R, Velasquez N, Poplawsky AJ, Coffman BA, Lee SE. Neuromapping olfactory stimulation using magnetoencephalography - visualizing smell, a proof-of-concept study. FRONTIERS IN ALLERGY 2023; 3:1019265. [PMID: 36698377 PMCID: PMC9869273 DOI: 10.3389/falgy.2022.1019265] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2022] [Accepted: 12/14/2022] [Indexed: 01/12/2023] Open
Abstract
Importance Currently, clinical assessment of olfaction is largely reliant on subjective methods that require patient participation. The objective method for measuring olfaction, using electroencephalogram (EEG) readings, can be supplemented with the improved temporal resolution of magnetoencephalography (MEG) for olfactory measurement that can delineate cortical and peripheral olfactory loss. MEG provides high temporal and spatial resolution which can enhance our understanding of central olfactory processing compared to using EEG alone. Objective To determine the feasibility of building an in-house portable olfactory stimulator paired with electrophysiological neuroimaging technique with MEG to assess olfaction in the clinical setting. Design setting and participants This proof-of-concept study utilized a paired MEG-olfactometer paradigm to assess olfaction in three normosmic participants. We used a two-channel olfactory stimulator to deliver odorants according to a programmed stimulus-rest paradigm. Two synthetic odorants: 2% phenethyl alcohol (rose) and 0.5% amyl acetate (banana) were delivered in increasing increments of time followed by periods of rest. Cortical activity was measured via a 306-channel MEG system. Main outcomes and measures Primary outcome measure was the relative spectral power for each frequency band, which was contrasted between rest and olfactory stimulation. Results Compared to rest, olfactory stimulation produced a 40% increase in relative alpha power within the olfactory cortex bilaterally with both odorants. A 25%-30% increase in relative alpha power occurred in the left orbitofrontal cortex and precentral gyrus with phenethyl alcohol stimulation but not amyl acetate. Conclusion and relevance In this proof-of-concept study, we demonstrate the feasibility of olfactory measurement via an olfactometer-MEG paradigm. We found that odorant-specific cortical signatures can be identified using this paradigm, setting the basis for further investigation of this system as a prognostic tool for olfactory loss.
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Affiliation(s)
- Rahilla Tarfa
- University of Pittsburgh School of Medicine, Pittsburgh, PA, United States,Department of Otolaryngology – Head and Neck Surgery, University of Pittsburgh Medical Center (UPMC), Pittsburgh, PA, United States
| | - Sophie E. Yu
- Department of Otolaryngology – Head & Neck Surgery, Harvard Medical School, Boston, MA, United States
| | - Omar H. Ahmed
- Penn Medicine Becker ENT & Allergy, Robbinsville, NJ, United States
| | - John A. Moore
- Department of Otolaryngology – Head and Neck Surgery, University of Pittsburgh Medical Center (UPMC), Pittsburgh, PA, United States
| | - Ricardo Bruña
- Department of Radiology, Universidad Complutense de Madrid (UCM), IdISSC, Madrid, Spain
| | - Nathalia Velasquez
- Department of Otolaryngology, Cleveland Clinic Florida, Weston, FL, United States
| | - Alexander J. Poplawsky
- Center for Neuroscience, McGowan Institute of Regenerative Medicine, University of Pittsburgh, Pittsburgh, PA, United States
| | - Brian A. Coffman
- Department of Psychiatry, University of Pittsburgh, Pittsburgh, PA, United States
| | - Stella E. Lee
- Division of Otolaryngology – Head & Neck Surgery, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, United States,Correspondence: Stella E. Lee
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Spatiotemporal dynamics of odor representations in the human brain revealed by EEG decoding. Proc Natl Acad Sci U S A 2022; 119:e2114966119. [PMID: 35584113 PMCID: PMC9173780 DOI: 10.1073/pnas.2114966119] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/05/2022] Open
Abstract
To elucidate when and where in the brain different aspects of odor perception emerge, we decoded odors from an electroencephalogram and associated the results with perception and source activities. The odor information was decoded 100 ms after odor onset at the earliest, with its signal sources estimated in and around the olfactory areas. The neural representation of odor unpleasantness emerged 300 ms after odor onset, followed by pleasantness and perceived quality at 500 ms. During this time, brain regions representing odor information spread rapidly from the olfactory areas to regions associated with emotional, semantic, and memory processing. The results suggested that odor perception emerges through computations in these areas, with different perceptual aspects having different spatiotemporal dynamics. How the human brain translates olfactory inputs into diverse perceptions, from pleasurable floral smells to sickening smells of decay, is one of the fundamental questions in olfaction. To examine how different aspects of olfactory perception emerge in space and time in the human brain, we performed time-resolved multivariate pattern analysis of scalp-recorded electroencephalogram responses to 10 perceptually diverse odors and associated the resulting decoding accuracies with perception and source activities. Mean decoding accuracies of odors exceeded the chance level 100 ms after odor onset and reached maxima at 350 ms. The result suggests that the neural representations of individual odors were maximally separated at 350 ms. Perceptual representations emerged following the decoding peak: unipolar unpleasantness (neutral to unpleasant) from 300 ms, and pleasantness (neutral to pleasant) and perceptual quality (applicability to verbal descriptors such as “fruity” or “flowery”) from 500 ms after odor onset, with all these perceptual representations reaching their maxima after 600 ms. A source estimation showed that the areas representing the odor information, estimated based on the decoding accuracies, were localized in and around the primary and secondary olfactory areas at 100 to 350 ms after odor onset. Odor representations then expanded into larger areas associated with emotional, semantic, and memory processing, with the activities of these later areas being significantly associated with perception. These results suggest that initial odor information coded in the olfactory areas (<350 ms) evolves into their perceptual realizations (300 to >600 ms) through computations in widely distributed cortical regions, with different perceptual aspects having different spatiotemporal dynamics.
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Bae J, Kim K, Moon SA, Choe HK, Jin Y, Kang WS, Moon C. Time Course of Odor Categorization Processing. Cereb Cortex Commun 2021; 2:tgab058. [PMID: 34746790 PMCID: PMC8567848 DOI: 10.1093/texcom/tgab058] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2021] [Revised: 09/13/2021] [Accepted: 09/14/2021] [Indexed: 11/13/2022] Open
Abstract
The brain’s mechanisms for categorizing different odors have long been a research focus. Previous studies suggest that odor categorization may involve multiple neurological processes within the brain with temporal and spatial neuronal activation. However, there is limited evidence regarding temporally mediated mechanisms in humans, especially millisecond odor processing. Such mechanisms may be important because different brain areas may play different roles at a particular activation time during sensory processing. Here, we focused on how the brain categorizes odors at specific time intervals. Using multivariate electroencephalography (EEG) analysis, we found that similarly perceived odors induced similar EEG signals during 50–100, 150–200, and 350–400 ms at the theta frequency. We also found significant activation at 100–150 and 350–400 ms at the gamma frequency. At these two frequencies, significant activation was observed in some olfactory-associated areas, including the orbitofrontal cortex. Our findings provide essential evidence that specific periods may be related to odor quality processing during central olfactory processing.
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Affiliation(s)
- Jisub Bae
- Brain Engineering Convergence Research Center, Daegu Gyeungbuk Institute of Science and Technology (DGIST), Daegu, South Korea
| | - Kwangsu Kim
- Department of Brain & Cognitive Sciences, Daegu Gyeungbuk Institute of Science and Technology (DGIST), Daegu, South Korea
| | - Sun Ae Moon
- Department of Brain & Cognitive Sciences, Daegu Gyeungbuk Institute of Science and Technology (DGIST), Daegu, South Korea
| | - Han Kyoung Choe
- Department of Brain & Cognitive Sciences, Daegu Gyeungbuk Institute of Science and Technology (DGIST), Daegu, South Korea
| | - Youngsun Jin
- Department of Psychology, Kyungpook National University, Daegu, South Korea
| | - Won-Seok Kang
- Convergence Research Advanced Centre for Olfaction, Daegu Gyeungbuk Institute of Science and Technology (DGIST), Daegu, South Korea
| | - Cheil Moon
- Department of Brain & Cognitive Sciences, Daegu Gyeungbuk Institute of Science and Technology (DGIST), Daegu, South Korea
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6
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Fjaeldstad AW, Stiller-Stut F, Gleesborg C, Kringelbach ML, Hummel T, Fernandes HM. Validation of Olfactory Network Based on Brain Structural Connectivity and Its Association With Olfactory Test Scores. Front Syst Neurosci 2021; 15:638053. [PMID: 33927597 PMCID: PMC8078209 DOI: 10.3389/fnsys.2021.638053] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2020] [Accepted: 03/08/2021] [Indexed: 01/26/2023] Open
Abstract
Olfactory perception is a complicated process involving multiple cortical and subcortical regions, of which the underlying brain dynamics are still not adequately mapped. Even in the definition of the olfactory primary cortex, there is a large degree of variation in parcellation templates used for investigating olfaction in neuroimaging studies. This complicates comparison between human olfactory neuroimaging studies. The present study aims to validate an olfactory parcellation template derived from both functional and anatomical data that applies structural connectivity (SC) to ensure robust connectivity to key secondary olfactory regions. Furthermore, exploratory analyses investigate if different olfactory parameters are associated with differences in the strength of connectivity of this structural olfactory fingerprint. By combining diffusion data with an anatomical atlas and advanced probabilistic tractography, we found that the olfactory parcellation had a robust SC network to key secondary olfactory regions. Furthermore, the study indicates that higher ratings of olfactory significance were associated with increased intra- and inter-hemispheric SC of the primary olfactory cortex. Taken together, these results suggest that the patterns of SC between the primary olfactory cortex and key secondary olfactory regions has potential to be used for investigating the nature of olfactory significance, hence strengthening the theory that individual differences in olfactory behaviour are encoded in the structural network fingerprint of the olfactory cortex.
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Affiliation(s)
- Alexander Wieck Fjaeldstad
- Flavour Institute, Department of Clinical Medicine, Aarhus University, Aarhus, Denmark.,Flavour Clinic, Department of Otorhinolaryngology, Holstebro Regional Hospital, Holstebro, Denmark.,Center for Eudaimonia and Human Flourishing, University of Oxford, Oxford, United Kingdom
| | - Franz Stiller-Stut
- Interdisciplinary Center for Smell and Taste, Department of Otorhinolaryngology, TU Dresden, Dresden, Germany
| | - Carsten Gleesborg
- Flavour Institute, Department of Clinical Medicine, Aarhus University, Aarhus, Denmark.,Center of Functionally Integrative Neuroscience, Aarhus University, Aarhus, Denmark
| | - Morten L Kringelbach
- Flavour Institute, Department of Clinical Medicine, Aarhus University, Aarhus, Denmark.,Center for Eudaimonia and Human Flourishing, University of Oxford, Oxford, United Kingdom.,Center of Music in the Brain, Aarhus University, Aarhus, Denmark
| | - Thomas Hummel
- Interdisciplinary Center for Smell and Taste, Department of Otorhinolaryngology, TU Dresden, Dresden, Germany
| | - Henrique M Fernandes
- Flavour Institute, Department of Clinical Medicine, Aarhus University, Aarhus, Denmark.,Center for Eudaimonia and Human Flourishing, University of Oxford, Oxford, United Kingdom.,Center of Music in the Brain, Aarhus University, Aarhus, Denmark
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7
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Odor habituation can modulate very early olfactory event-related potential. Sci Rep 2020; 10:18117. [PMID: 33093624 PMCID: PMC7582193 DOI: 10.1038/s41598-020-75263-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2020] [Accepted: 10/08/2020] [Indexed: 11/08/2022] Open
Abstract
Odor habituation is a phenomenon that after repeated exposure to an odor, is characterized by decreased responses to it. The central nervous system is involved in odor habituation. To study odor habituation in humans, measurement of event-related potentials (ERPs) has been widely used in the olfactory system and other sensory systems, because of their high temporal resolution. Most previous odor habituation studies have measured the olfactory ERPs of (200-800) ms. However, several studies have shown that the odor signal is processed in the central nervous system earlier than at 200 ms. For these reasons, we studied whether when odors were habituated, olfactory ERP within 200 ms of odors could change. To this end, we performed an odor habituation behavior test and electroencephalogram experiments. In the behavior test, under habituation conditions, odor intensity was significantly decreased. We found significant differences in the negative and positive potentials within 200 ms across the conditions, which correlated significantly with the results of the behavior test. We also observed that ERP latency depended on the conditions. Our study suggests that odor habituation can involve the olfactory ERP of odors within 200 ms in the brain.
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8
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Okumura T, Kumazaki H, Singh AK, Touhara K, Okamoto M. Individuals With Autism Spectrum Disorder Show Altered Event-Related Potentials in the Late Stages of Olfactory Processing. Chem Senses 2020; 45:37-44. [PMID: 31711116 DOI: 10.1093/chemse/bjz070] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Atypical sensory reactivities are pervasive among people with autism spectrum disorder (ASD). With respect to olfaction, most previous studies have used psychophysical or questionnaire-based methodologies; thus, the neural basis of olfactory processing in ASD remains unclear. This study aimed to determine the stages of olfactory processing that are altered in ASD. Fourteen young adults with high-functioning ASD (mean age, 21 years; 3 females) were compared with 19 age-matched typically developing (TD) controls (mean age, 21 years; 4 females). Olfactory event-related potentials (OERPs) for 2-phenylethyl alcohol-a rose-like odor-were measured with 64 scalp electrodes while participants performed a simple odor detection task. Significant group differences in OERPs were found in 3 time windows 542 ms after the stimulus onset. The cortical source activities in these time windows, estimated using standardized low-resolution brain electromagnetic tomography, were significantly higher in ASD than in TD in and around the posterior cingulate cortex, which is known to play a crucial role in modality-general cognitive processing. Supplemental Bayesian analysis provided substantial evidence for an alteration in the later stages of olfactory processing, whereas conclusive evidence was not provided for the earlier stages. These results suggest that olfactory processing in ASD is altered at least at the later, modality-general processing stage.
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Affiliation(s)
- Toshiki Okumura
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, University of Tokyo, Tokyo, Japan
| | - Hirokazu Kumazaki
- Department of Preventive Intervention for Psychiatric Disorders, National Institute of Mental Health, National Center of Neurology and Psychiatry, Tokyo, Japan
| | - Archana K Singh
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, University of Tokyo, Tokyo, Japan.,ERATO Touhara Chemosensory Signal Project, JST, University of Tokyo, Tokyo, Japan
| | - Kazushige Touhara
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, University of Tokyo, Tokyo, Japan.,ERATO Touhara Chemosensory Signal Project, JST, University of Tokyo, Tokyo, Japan.,WPI International Research Center for Neurointelligence, University of Tokyo Institutes for Advanced Study, Tokyo, Japan
| | - Masako Okamoto
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, University of Tokyo, Tokyo, Japan.,ERATO Touhara Chemosensory Signal Project, JST, University of Tokyo, Tokyo, Japan
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Coquery N, Menneson S, Meurice P, Janvier R, Etienne P, Noirot V, Val-Laillet D. fMRI-Based Brain Responses to Olfactory Stimulation with Two Putatively Orexigenic Functional Food Ingredients at Two Different Concentrations in the Pig Model. J Food Sci 2019; 84:2666-2673. [PMID: 31441517 DOI: 10.1111/1750-3841.14772] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2019] [Revised: 07/10/2019] [Accepted: 07/19/2019] [Indexed: 11/29/2022]
Abstract
Natural plant extracts are increasingly used as functional feed ingredients in animal husbandry and food ingredients in human alternative medicine to improve welfare and health. We investigated in 20 growing pigs via functional magnetic resonance imaging (fMRI) the brain blood oxygen level-dependent (BOLD) responses to olfactory stimulation with two sensory functional feed ingredients, A and B, at two different concentrations. Functional ingredient A contained extracts from Citrus sinensis (60% to 80%), and ingredient B contained a mixture of extracts Oreganum vulgarae (40% to 55%) and Cymbopogon flexuosus (20% to 25%). Increased concentration of ingredients induced a higher activation in reward and cognitive areas compared to lower concentrations. Moreover, considering both ingredients at the highest concentration, the ingredient A elicited higher brain responses in brain areas involved in hedonism/pleasantness compared to ingredient B, and more specifically in the caudate nucleus and orbitofrontal cortex. Our findings shed new light in the scope of emotion regulation through olfactory modulation via sensory functional ingredients, which opens the way to further preclinical studies in animal models and translational research in the context of nutrition, welfare, and health. PRACTICAL APPLICATION: Functional food/feed ingredients are gaining interest for improving health and welfare in humans and animals. Besides representing an alternative to antibiotics for example, food ingredients and their sensory characteristics might have a positive impact on emotions and consequently on well-being. Functional brain imaging in large animals such as in the pig model is a promising approach to investigate the central and behavioural effects of food ingredients, and determine the most effective blends and concentrations to modulate internal and emotional states.
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Affiliation(s)
- Nicolas Coquery
- INRA, INSERM, Univ. Rennes, Nutrition Metabolisms and Cancer, NuMeCan, Rennes, France
| | - Sophie Menneson
- INRA, INSERM, Univ. Rennes, Nutrition Metabolisms and Cancer, NuMeCan, Rennes, France.,Phodé, Terssac, France
| | - Paul Meurice
- INRA, INSERM, Univ. Rennes, Nutrition Metabolisms and Cancer, NuMeCan, Rennes, France
| | - Régis Janvier
- INRA, INSERM, Univ. Rennes, Nutrition Metabolisms and Cancer, NuMeCan, Rennes, France
| | | | | | - David Val-Laillet
- INRA, INSERM, Univ. Rennes, Nutrition Metabolisms and Cancer, NuMeCan, Rennes, France
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10
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Sirous M, Sinning N, Schneider TR, Friese U, Lorenz J, Engel AK. Chemosensory Event-Related Potentials in Response to Nasal Propylene Glycol Stimulation. Front Hum Neurosci 2019; 13:99. [PMID: 30949040 PMCID: PMC6435593 DOI: 10.3389/fnhum.2019.00099] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2018] [Accepted: 03/04/2019] [Indexed: 11/13/2022] Open
Abstract
Propylene glycol, also denoted as 1.2 propanediol (C3H8O2), often serves as a solvent for dilution of olfactory stimuli. It is supposed to serve as a neutral substance and has been used in many behavioral and electrophysiological studies to dilute pure olfactory stimuli. However, the effect of propylene glycol on perception and on neuronal responses has hitherto never been studied. In this study we tested by means of a threshold test, whether a nasal propylene glycol stimulation is recognizable by humans. Participants were able to recognize propylene glycol at a threshold of 42% concentration and reported a slight cooling effect. In addition to the threshold test, we recorded electroencephalography (EEG) during nasal propylene glycol stimulation to study the neuronal processing of the stimulus. We used a flow olfactometer and stimulated 15 volunteers with three different concentrations of propylene glycol (40 trials each) and water as a control condition (40 trials). To evaluate the neuronal response, we analyzed the event-related potentials (ERPs) and power modulations. The task of the volunteers was to identify a change (olfactory, thermal, or tactile) in the continuous air flow generated by the flow olfactometer. The analysis of the ERPs showed that propylene glycol generates a clear P2 component, which was also visible in the frequency domain as an evoked power response in the theta-band. The source analysis of the P2 revealed a widespread involvement of brain regions, including the postcentral gyrus, the insula and adjacent operculum, the thalamus, and the cerebellum. Thus, it is possible that trigeminal stimulation can at least partly account for sensations and brain responses elicited by propylene glycol. Based on these results, we conclude that the use of high propylene glycol concentrations to dilute fragrances complicates the interpretation of presumed purely olfactory effects.
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Affiliation(s)
- Mohammad Sirous
- Department of Neurophysiology and Pathophysiology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Nico Sinning
- Department of Neurophysiology and Pathophysiology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Till R Schneider
- Department of Neurophysiology and Pathophysiology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Uwe Friese
- Department of Neurophysiology and Pathophysiology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.,Faculty of Life Science, MSH Medical School Hamburg, Hamburg, Germany
| | - Jürgen Lorenz
- Faculty of Life Science, Laboratory of Human Biology and Physiology, Applied Science University, Hamburg, Germany
| | - Andreas K Engel
- Department of Neurophysiology and Pathophysiology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
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11
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Gotow N, Kobayakawa T. Trial measurement of brain activity underlying olfactory-gustatory synchrony perception using event-related potentials from five female participants. J Neurosci Res 2018; 97:253-266. [PMID: 30125987 DOI: 10.1002/jnr.24310] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2017] [Revised: 06/15/2018] [Accepted: 07/03/2018] [Indexed: 11/10/2022]
Abstract
Temporal synchrony between odor and taste plays an important role in flavor perception. When we investigate temporal synchrony between odor and taste, it is necessary to pay attention not only to physical simultaneity of the presentation of olfactory and gustatory stimuli, but also to the perceptual simultaneity between the two stimuli. In this study, we examined short-latency brain activity underlying synchrony perception for olfactory-gustatory combinations. While five female participants performed a simultaneity judgment (SJ) task using soy sauce odor and salt solution, single-channel event-related potentials (ERPs) were recorded at the position of Cz. In each trial, the participant was asked whether olfactory and gustatory stimuli were perceived simultaneously or successively. Based on the judgment responses acquired from participants (i.e., simultaneous or successive), ERP data were classified into two datasets. The means of ERPs from each participant were calculated for each type of judgment response, considering the onset of olfactory or gustatory stimuli (OERPs or GERPs, respectively) as the starting point. The latencies of the P1 component of GERPs were very similar between simultaneous and successive judgment responses, whereas the P1 amplitudes differed significantly. These results indicated that neural activity affecting SJ for an olfactory-gustatory combination is generated during a period of about 130 ms from the onset of gustatory stimulus. Thus, olfactory and gustatory information processing related to flavor perception (more specially, synchrony perception between odor and taste) might be initiated at a relatively early stage of the central pathway.
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Affiliation(s)
- Naomi Gotow
- Human Informatics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan
| | - Tatsu Kobayakawa
- Human Informatics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan
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