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Journal of Neural Engineering Oct 2021The emotional response to olfactory stimuli implies the activation of a complex cascade of events triggered by structures lying in the limbic system. However, little is...
The emotional response to olfactory stimuli implies the activation of a complex cascade of events triggered by structures lying in the limbic system. However, little is known about how this activation is projected up to cerebral cortex and how different cortical areas dynamically interact each other.In this study, we acquired EEG from human participants performing a passive odor-perception task with odorants conveying positive, neutral and negative valence. A novel methodological pipeline integrating global field power (GFP), independent component analysis (ICA), dipole source localization was applied to estimate effective connectivity in the challenging scenario of single-trial low-synchronized stimulation.We identified the brain network and the neural paths, elicited at different frequency bands, i.e.θ(4-7Hz),α(8-12Hz)andβ(13-30Hz), involved in odor valence processing. This brain network includes the orbitofrontal cortex (OFC), the cingulate gyrus (CgG), the superior temporal gyrus (STG), the posterior cingulate cortex/precuneus (PCC/PCu) and the parahippocampal gyrus (PHG). It was analyzed using a time-varying multivariate autoregressive model to resolve time-frequency causal interactions. Specifically, the OFC acts as the main node for odor perception and evaluation of pleasant and unpleasant stimuli, whereas no specific path was observed for a neutral stimulus.The results introduce new evidences on the role of the OFC during hedonic perception and underpin its specificity during the odor valence assessment. Our findings suggest that, after the odor onset different, bidirectional interactions occur between the OFC and other brain regions associated with emotion recognition/categorization and memory according to the stimulus valence. This outcome unveils how the hedonic olfactory network dynamically changes based on odor valence.
Topics: Brain; Cerebral Cortex; Humans; Magnetic Resonance Imaging; Olfactory Perception; Smell
PubMed: 34547740
DOI: 10.1088/1741-2552/ac28d2 -
Annual Review of Neuroscience 2010Although the lifelong addition of new neurons to the olfactory bulb and dentate gyrus of mammalian brains is by now an accepted fact, the function of adult-generated... (Review)
Review
Although the lifelong addition of new neurons to the olfactory bulb and dentate gyrus of mammalian brains is by now an accepted fact, the function of adult-generated neurons still largely remains a mystery. The ability of new neurons to form synapses with preexisting neurons without disrupting circuit function is central to the hypothesized role of adult neurogenesis as a substrate for learning and memory. With the development of several new genetic labeling and imaging techniques, the study of synapse development and integration of these new neurons into mature circuits both in vitro and in vivo is rapidly advancing our insight into their structural plasticity. Investigators' observation of synaptogenesis occurring in the adult brain is beginning to shed light on the flexibility that adult neurogenesis offers to mature circuits and the potential contribution of the transient plasticity that new neurons provide toward circuit refinement and adaptation to changing environmental demands.
Topics: Adaptation, Physiological; Animals; Dentate Gyrus; Humans; Neurogenesis; Neuronal Plasticity; Olfactory Bulb; Synapses
PubMed: 20572770
DOI: 10.1146/annurev-neuro-060909-153252 -
Brain Structure & Function Jan 2022Brain structural features of healthy individuals are associated with olfactory functions. However, due to the pathophysiological differences, congenital and acquired...
Brain structural features of healthy individuals are associated with olfactory functions. However, due to the pathophysiological differences, congenital and acquired anosmia may exhibit different structural characteristics. A systematic review was undertaken to compare brain structural features between patients with congenital and acquired anosmia. A systematic search was conducted using PubMed/MEDLINE and Scopus electronic databases to identify eligible reports on anosmia and structural changes and reported according to PRISMA guidelines. Reports were extracted for information on demographics, psychophysical evaluation, and structural changes. Then, the report was systematically reviewed based on various aetiologies of anosmia in relation to (1) olfactory bulb, (2) olfactory sulcus, (3) grey matter (GM), and white matter (WM) changes. Twenty-eight published studies were identified. All studies reported consistent findings with strong associations between olfactory bulb volume and olfactory function across etiologies. However, the association of olfactory function with olfactory sulcus depth was inconsistent. The present study observed morphological variations in GM and WM volume in congenital and acquired anosmia. In acquired anosmia, reduced olfactory function is associated with reduced volumes and thickness involving the gyrus rectus, medial orbitofrontal cortex, anterior cingulate cortex, and cerebellum. These findings contrast to those observed in congenital anosmia, where a reduced olfactory function is associated with a larger volume and higher thickness in parts of the olfactory network, including the piriform cortex, orbitofrontal cortex, and insula. The present review proposes that the structural characteristics in congenital and acquired anosmia are altered differently. The mechanisms behind these changes are likely to be multifactorial and involve the interaction with the environment.
Topics: Anosmia; Brain; Gray Matter; Humans; Magnetic Resonance Imaging; Olfaction Disorders
PubMed: 34635958
DOI: 10.1007/s00429-021-02397-3 -
Epilepsy & Behavior : E&B Jan 2021Olfactory hallucinations can be part of epileptic seizures of orbitofrontal origin. Olfactory hallucinations, however, are rare and therefore the semiology, localization...
BACKGROUND
Olfactory hallucinations can be part of epileptic seizures of orbitofrontal origin. Olfactory hallucinations, however, are rare and therefore the semiology, localization and lateralization characteristics are underdetermined. In addition, many discrepancies are found in the literature regarding olfactory processing and orbitofrontal (OF) functions and olfactory function. Particularly, the questions of laterality and affective component in coding of odors in the OF cortex remain controversial.
AIMS
This study explored whether cortical electrical stimulation of the OF and mesiotemporal brain can trigger olfactory hallucinations with special focus on olfactory percepts in terms of laterality and hedonics.
MATERIALS AND METHODS
Eight patients with temporal lobe epilepsy participated in the study, at the time of invasive exploration of their epilepsy. The most distal contact of the OF and anterior hippocampus depth electrodes were stimulated (50 Hz, 0.2 ms biphasic pulse; maximal stimulation 4 mA). Patients were instructed to report any kind of sensation they might experience. Intracranial depth electrodes were localized (iElectrodes): subject-specific brain mask, subcortical segmentation and cortical parcellation based on the Destrieux atlas (FreeSurfer) were superposed to the coregistered T1-weighted MRI and CT images (SPM). The center of mass of each electrode-artifact cluster determined the electrode localization. The electrode labeling was done in patient space. To obtain the electrode coordinates in Montreal Neurological Institute (MNI) space, the images obtained previously in the patient space were first segmented and normalized (SPM). Then, the localization procedure (iElectrodes) was run again with these new normalized images in MNI space.
RESULTS
No hallucination was evoked by stimulation, neither of the right nor the left hippocampus (8/8 patients). Pleasant olfactory hallucinations were evoked by OF stimulation in 5/8 patients in either hemisphere. Patients named the percept as the smell of lemon or coffee for example. Among those 5 patients, electrodes were localized in the cortex of the olfactory sulcus, medial orbital sulcus or medial OF gyrus. Increasing stimulation amplitude changed the olfactory percept identification in 3 out of those 5 patients. No affective judgement or change in perceived odor intensity was reported by the patients. No hallucination was evoked by the stimulation of the white matter of the medial OF brain in 3/8 patients independently of the hemisphere stimulated.
CONCLUSIONS
This study demonstrated that stimulation of the cortex of the medial OF brain and not of its white matter elicits specific pleasant olfactory hallucinations independently of the hemisphere stimulated, supporting one symmetrical olfactory processing in human.
Topics: Cerebral Cortex; Electric Stimulation; Electroencephalography; Humans; Magnetic Resonance Imaging; Olfactory Perception; Prefrontal Cortex
PubMed: 33243684
DOI: 10.1016/j.yebeh.2020.107559 -
Human Brain Mapping Jun 2022In recent years, multisensory integration of visual and olfactory stimuli has extensively been explored resulting in the identification of responsible brain areas. As...
In recent years, multisensory integration of visual and olfactory stimuli has extensively been explored resulting in the identification of responsible brain areas. As the experimental designs of previous research often include alternating presentations of unimodal and bimodal stimuli, the conditions cannot be regarded as completely independent. This could lead to effects of an expected but surprisingly missing sensory modality. In our experiment, we used a common functional magnetic resonance imaging (fMRI) study design with alternating strong unimodal and bimodal olfactory-visual food stimuli, in addition to a slight overhang of the bimodal stimuli in an effort to examine the effects of removing a visual or olfactory congruent stimulus for older people (41-83 years). Our results suggest that the processing of olfactory and visual stimuli stays intact over a wide age-range and that the utilization of strong stimuli does not lead to superadditive multisensory integration in accordance with the principle of inverse effectiveness. However, our results demonstrate that the removal of a stimulus modality leads to an activation of additional brain areas. For example, when the visual stimulus modality is missing, the right posterior superior temporal gyrus shows higher activation, whereas the removal of the olfactory stimulus modality leads to higher activation in the amygdala/hippocampus and the postcentral gyrus. These brain areas are related to attention, memory, and the search of the missing stimulus. Consequently, careful attention must be paid to the design of a valid, multimodal sensory experiment while also controlling for cognitive expectancy effects that might confound multimodal results.
Topics: Acoustic Stimulation; Aged; Auditory Perception; Brain; Brain Mapping; Humans; Magnetic Resonance Imaging; Photic Stimulation; Smell; Visual Perception
PubMed: 35142405
DOI: 10.1002/hbm.25806 -
Journal of Alzheimer's Disease : JAD 2022The olfactory system is affected very early in Alzheimer's disease and olfactory loss can already be observed in patients with mild cognitive impairment (MCI), an early... (Randomized Controlled Trial)
Randomized Controlled Trial
BACKGROUND
The olfactory system is affected very early in Alzheimer's disease and olfactory loss can already be observed in patients with mild cognitive impairment (MCI), an early stage of AD.
OBJECTIVE
The aim of this randomized, prospective, controlled, blinded study was to evaluate whether olfactory training (OT) may have an effect on olfactory function, cognitive impairment, and brain activation in MCI patients after a 4-month period of frequent short-term exposure to various odors.
METHODS
A total of 38 MCI outpatients were randomly assigned to OT or a control training condition, which were performed twice a day for 4 months. Olfactory testing, comprehensive neuropsychological assessment, and a passive odor perception task based on magnetic resonance imaging were performed before and after training.
RESULTS
The results suggested that OT exhibited no significant effect on olfaction and cognitive function. Additionally, OT exhibited a positive effect on frontal lobe activation (left middle frontal gyrus and orbital-frontal cortex) but exhibited no effect on grey matter volume. Moreover, the change of olfactory scores was positively associated with the change of frontal activation.
CONCLUSION
OT was found to have a limited effect on olfaction and cognition in patients with MCI compared to a non-OT condition but increased their functional response to odors in frontal area.
Topics: Aged; Brain; Cognition; Cognitive Dysfunction; Female; Humans; Magnetic Resonance Imaging; Male; Middle Aged; Neuropsychological Tests; Odorants; Olfaction Disorders; Prospective Studies; Smell
PubMed: 34864678
DOI: 10.3233/JAD-215257 -
Scientific Reports Aug 2023We aimed to investigate changes in olfactory bulb volume and brain network in the white matter (WM) in patients with persistent olfactory disfunction (OD) following...
We aimed to investigate changes in olfactory bulb volume and brain network in the white matter (WM) in patients with persistent olfactory disfunction (OD) following COVID-19. A cross-sectional study evaluated 38 participants with OD after mild COVID-19 and 24 controls, including Sniffin' Sticks identification test (SS-16), MoCA, and brain magnetic resonance imaging. Network-Based Statistics (NBS) and graph theoretical analysis were used to explore the WM. The COVID-19 group had reduced olfactory bulb volume compared to controls. In NBS, COVID-19 patients showed increased structural connectivity in a subnetwork comprising parietal brain regions. Regarding global network topological properties, patients exhibited lower global and local efficiency and higher assortativity than controls. Concerning local network topological properties, patients had reduced local efficiency (left lateral orbital gyrus and pallidum), increased clustering (left lateral orbital gyrus), increased nodal strength (right anterior orbital gyrus), and reduced nodal strength (left amygdala). SS-16 test score was negatively correlated with clustering of whole-brain WM in the COVID-19 group. Thus, patients with OD after COVID-19 had relevant WM network dysfunction with increased connectivity in the parietal sensory cortex. Reduced integration and increased segregation are observed within olfactory-related brain areas might be due to compensatory plasticity mechanisms devoted to recovering olfactory function.
Topics: Humans; Diffusion Tensor Imaging; Cross-Sectional Studies; COVID-19; Brain; White Matter; Magnetic Resonance Imaging
PubMed: 37558765
DOI: 10.1038/s41598-023-40115-7 -
European Archives of... Mar 2023Cigarette smoking remains a serious health problem all over the world. We investigated the peripheral and central olfactory pathways in young male smokers to determine...
OBJECTIVES
Cigarette smoking remains a serious health problem all over the world. We investigated the peripheral and central olfactory pathways in young male smokers to determine whether there is a relationship between the amount of cigarettes smoked and duration of smoking and the dimensions of the olfactory areas.
METHODS
In this retrospective study, cranial Magnetic Resonance Imaging (MRI) images of adult male smokers aged ≤ 40 years (n = 51) and 50 healthy male adults were analyzed. The olfactory bulbus (OB) volumes and olfactory sulcus (OS) depths, insular gyrus, and corpus amygdala areas were measured via cranial MRI. In the smoker group, the number of cigarettes smoked and duration of smoking were noted and the Brinkmann index was calculated.
RESULTS
OB volume, OS depth, and the insular gyrus areas of the smokers were lower than in the control group (p < 0.05). There were no differences between the groups in terms of the corpus amygdala measurements (p > 0.05). No significant correlations were found between the number of cigarettes smoked daily, smoking duration, and the Brinkmann index and the peripheral and central olfactory measurements in our study (p > 0.05).
CONCLUSIONS
In smokers, OB volumes, the OS, and the central areas decrease bilaterally, regardless of smoking duration and number of cigarettes smoked daily. This could be related to inflammatory mediators that may be harmful to the olfactory neuroepithelium, gray matter atrophy in the brain, or endothelial damage related to smoking and its effects on blood support to the brain and olfactory regions.
Topics: Adult; Humans; Male; Smokers; Olfaction Disorders; Retrospective Studies; Smell; Magnetic Resonance Imaging; Olfactory Bulb
PubMed: 36242611
DOI: 10.1007/s00405-022-07700-4 -
Laryngo- Rhino- Otologie Aug 2007Olfactory dysfunction has been reported to affect about 79,000 patients who were treated annually in German ORL-hospitals. The incidence of olfactory dysfunctions... (Review)
Review
Olfactory dysfunction has been reported to affect about 79,000 patients who were treated annually in German ORL-hospitals. The incidence of olfactory dysfunctions emphasizes the need for diagnostic strategies. This article features on the dysfunction of human olfaction including neurodegenerative diseases. Standard procedures for the psychophysical and objective assessment of olfactory function are presented. Current diagnostic imaging techniques for routine use and scientific approaches are discussed.
Topics: Adrenal Cortex Hormones; Amygdala; Chemoreceptor Cells; Electroencephalography; Equipment Design; Evoked Potentials; Gyrus Cinguli; Humans; Magnetic Resonance Imaging; Neurodegenerative Diseases; Olfaction Disorders; Olfactory Nerve Diseases; Olfactory Pathways; Otolaryngology; Sensory Thresholds; Smell; Tomography, X-Ray Computed; Trigeminal Nerve
PubMed: 17665356
DOI: 10.1055/s-2007-966532 -
Genes To Cells : Devoted To Molecular &... Oct 2006Neurogenesis in the subgranular zone of the hippocampal dentate gyrus and olfactory bulbs continues into adulthood and has been implicated in the cognitive function of...
Neurogenesis in the subgranular zone of the hippocampal dentate gyrus and olfactory bulbs continues into adulthood and has been implicated in the cognitive function of the adult brain. The basal forebrain cholinergic system has been suggested to play a role in regulating neurogenesis as well as learning and memory in these regions. Herein, we report that highly polysialylated neural cell adhesion molecule (PSA-NCAM)-positive immature cells as well as neuronal nuclei (NeuN)-positive mature neurons in the dentate gyrus and olfactory bulb express multiple acetylcholine receptor subunits and make contact with cholinergic fibers. To examine the function of acetylcholine in neurogenesis, we used donepezil (Aricept), a potent and selective acetylcholinesterase inhibitor that improves cognitive impairment in Alzheimer's disease. Intraperitoneal administrations of donepezil significantly enhanced the survival of newborn neurons, but not proliferation of neural progenitor cells in the subgranular zone or the subventricular zone of normal mice. Moreover, donepezil treatment reversed the chronic stress-induced decrease in neurogenesis. Taken together, these results suggest that activation of the cholinergic system promotes survival of newborn neurons in the adult dentate gyrus and olfactory bulb under both normal and stressed conditions.
Topics: Acetylcholine; Animals; Animals, Newborn; Cell Survival; Cholinergic Fibers; Cholinesterase Inhibitors; Dentate Gyrus; Donepezil; Humans; Indans; Male; Mice; Mice, Inbred C57BL; Neurons; Olfactory Bulb; Piperidines; Receptors, Cholinergic
PubMed: 16999735
DOI: 10.1111/j.1365-2443.2006.01010.x