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Reviews in the Neurosciences 2004This review summarizes research that correlates behavioral performance and cellular physiology leading to modifications in the neuronal networks supporting long-term... (Review)
Review
This review summarizes research that correlates behavioral performance and cellular physiology leading to modifications in the neuronal networks supporting long-term memory in the mammalian brain. Rats were trained in an olfactory associative discrimination task in which natural odors were replaced by mimetic olfactory stimulations. Olfactory learning induced synaptic modifications that affected behavioral performance along the central olfactory pathways. Starting with an early increase in monosynaptic efficacy in the dentate gyrus on the first session, a polysynaptic modification appeared later on in this hippocampal network, when rats began to make associations between cues and rewards. Therefore, only when rats made consistent associations did a long-term potentiation in the synapses of the piriform cortex pyramidal neurons appear. These modifications may correspond to the long-term storage of the meaning of the cue-reward association in a specific cortical area. Based on these cumulative results, a hypothesis is proposed to account for how, when, and where synaptic modifications in neural networks are required to constitute long-term memory.
Topics: Animals; Cats; Discrimination, Psychological; Memory; Nerve Net; Neural Networks, Computer; Neuronal Plasticity; Olfactory Pathways; Rats; Synapses
PubMed: 15046196
DOI: 10.1515/revneuro.2004.15.1.1 -
Neuron May 2011Recently, investigation of new neurons in memory formation has focused on a specific function-pattern separation. However, it has been difficult to reconcile the form of... (Review)
Review
Recently, investigation of new neurons in memory formation has focused on a specific function-pattern separation. However, it has been difficult to reconcile the form of separation tested in behavioral tasks with how it is conceptualized according to computational and electrophysiology perspectives. Here, we propose a memory resolution hypothesis that considers the unique information contributions of broadly tuned young neurons and highly specific mature neurons and describe how the fidelity of memories can relate to spatial and contextual discrimination. See the related Perspective from Sahay, Wilson, and Hen, "Pattern Separation: A Common Function for New Neurons in Hippocampus and Olfactory Bulb," in this issue of Neuron.
Topics: Adult; Age Factors; Animals; Dentate Gyrus; Humans; Memory; Neurogenesis
PubMed: 21609818
DOI: 10.1016/j.neuron.2011.05.010 -
Brain Research Mar 1996Normal rats offered a choice between scented and unscented food pellets: (a) avoid food scented with toluene (an aromatic organic solvent) or 2-propylthietane (a...
Normal rats offered a choice between scented and unscented food pellets: (a) avoid food scented with toluene (an aromatic organic solvent) or 2-propylthietane (a component of the anal scent gland secretions of weasels); (b) prefer food scented with cadaverine (a diamine component of the odor of rotting flesh); but (c) neither prefer nor avoid food scented with butyric acid (a component of the odor of rancid butter) or caproic acid (a component of the odor of goats). Lesions of the dentate gyrus and CA1 (induced by local injections of colchicine) and/or the neocortex overlying the hippocampus produce a complex pattern of changes in these normal olfactory reactions, but do not affect the normal reaction to food flavored with sucrose or quinine. Cell loss in the hippocampal formation results in an abnormal aversion to butyric acid, in particular, but neocortical damage also alters the behavioral reaction to scented food. The results are consistent with the view that the hippocampal formation and the neocortex play differing roles in the olfactory control of behavior.
Topics: Animals; Cerebral Cortex; Colchicine; Dentate Gyrus; Feeding Behavior; Rats; Smell; Stereotaxic Techniques
PubMed: 8814895
DOI: 10.1016/0006-8993(95)01416-0 -
European Journal of Nuclear Medicine... May 2022Hyposmia is a common feature of COVID-19 and Parkinson's disease (PD). As parkinsonism has been reported after COVID-19, a link has been hypothesized between SARS-CoV2...
PURPOSE
Hyposmia is a common feature of COVID-19 and Parkinson's disease (PD). As parkinsonism has been reported after COVID-19, a link has been hypothesized between SARS-CoV2 infection and PD. We aimed to evaluate brain metabolic correlates of isolated persistent hyposmia after mild-to-moderate COVID-19 and to compare them with metabolic signature of hyposmia in drug-naïve PD patients.
METHODS
Forty-four patients who experienced hyposmia after SARS-COV2 infection underwent brain [F]-FDG PET in the first 6 months after recovery. Olfaction was assessed by means of the 16-item "Sniffin' Sticks" test and patients were classified as with or without persistent hyposmia (COVID-hyposmia and COVID-no-hyposmia respectively). Brain [F]-FDG PET of post-COVID subgroups were compared in SPM12. COVID-hyposmia patients were also compared with eighty-two drug-naïve PD patients with hyposmia. Multiple regression analysis was used to identify correlations between olfactory test scores and brain metabolism in patients' subgroups.
RESULTS
COVID-hyposmia patients (n = 21) exhibited significant hypometabolism in the bilateral gyrus rectus and orbitofrontal cortex with respect to COVID-non-hyposmia (n = 23) (p < 0.002) and in middle and superior temporal gyri, medial/middle frontal gyri, and right insula with respect to PD-hyposmia (p < 0.012). With respect to COVID-hyposmia, PD-hyposmia patients showed hypometabolism in inferior/middle occipital gyri and cuneus bilaterally. Olfactory test scores were directly correlated with metabolism in bilateral rectus and medial frontal gyri and in the right middle temporal and anterior cingulate gyri in COVID-hyposmia patients (p < 0.006) and with bilateral cuneus/precuneus and left lateral occipital cortex in PD-hyposmia patients (p < 0.004).
CONCLUSION
Metabolic signature of persistent hyposmia after COVID-19 encompasses cortical regions involved in olfactory perception and does not overlap metabolic correlates of hyposmia in PD.
Topics: Anosmia; COVID-19; Fluorodeoxyglucose F18; Humans; Olfaction Disorders; Parkinson Disease; RNA, Viral; SARS-CoV-2; Smell
PubMed: 34984501
DOI: 10.1007/s00259-021-05666-9 -
Cephalalgia : An International Journal... Oct 2008Olfactory hypersensitivity (OHS) may occur during migraine attacks and seems to be very specific to this form of headache. OHS is also observed during migraine-free...
Olfactory hypersensitivity (OHS) may occur during migraine attacks and seems to be very specific to this form of headache. OHS is also observed during migraine-free periods and is associated with the presence of odour-triggered attacks. Yet the pathophysiology of OHS remains unknown. The aim of our study was to evaluate olfactory processing in migraineurs with OHS and to investigate whether regional cerebral blood flow (rCBF) associated with olfactory stimulation is modified in these patients compared with controls. Eleven migraineurs with OHS and 12 controls participated in a H(2)(15)O-positron emission tomography study, including three scans in which odours were delivered and three scans where only odourless air was delivered. rCBF during olfactory condition was compared with that for the odourless baseline condition. Between-group analyses were performed using voxel-based and region-of-interest analyses. During both olfactory and non-olfactory conditions, we observed higher rCBF in the left piriform cortex and antero-superior temporal gyrus in migraineurs compared with controls. During odour stimulation, migraineurs also showed significantly higher activation than controls in the left temporal pole and significantly lower activation in the frontal (left inferior as well as left and right middle frontal gyri) and temporo-parietal (left and right angular, and right posterior superior temporal gyri) regions, posterior cingulate gyrus and right locus coeruleus. These results could reflect a particular role of both the piriform cortex and antero-superior temporal gyrus in OHS and odour-triggered migraine. Whether these rCBF changes are the cause or a consequence of odour-triggered migraines and interictal OHS remains unknown. Further comparisons between migraineurs with and without OHS are warranted to address this issue. The abnormal cerebral activation patterns during olfactory stimulation might reflect altered cerebrovascular response to olfactory stimulation due to the migraine disease, or an abnormal top-down regulation process related to OHS.
Topics: Adult; Female; Humans; Middle Aged; Migraine Disorders; Odorants; Olfaction Disorders; Olfactory Pathways; Oxygen Radioisotopes; Positron-Emission Tomography; Young Adult
PubMed: 18727640
DOI: 10.1111/j.1468-2982.2008.01672.x -
Journal of Neurotrauma Nov 2018Olfactory loss and traumatic brain injury (TBI) both lead to anatomical brain alterations in humans. Little research has been done on the structural brain changes for...
Olfactory loss and traumatic brain injury (TBI) both lead to anatomical brain alterations in humans. Little research has been done on the structural brain changes for TBI patients with olfactory loss. Using voxel-based morphometry, the gray matter (GM) density was examined for 22 TBI patients with hyposmia, 24 TBI patients with anosmia, and 22 age-matched controls. Olfactory bulb (OB) volumes were measured by manual segmentation of acquired T2-weighted coronal slices using a standardized protocol. Brain lesions in the olfactory-relevant areas also were examined for TBI patients. Results showed that patients with anosmia have more frequent lesions in the OB, orbitofrontal cortex (OFC), and the temporal lobe pole, compared with patients with hyposmia. GM density in the primary olfactory area was decreased in both groups of patients. In addition, compared with controls, patients with anosmia showed GM density reduction in several secondary olfactory eloquent regions, including the gyrus rectus, medial OFC, anterior cingulate cortex, insula, and cerebellum. However, patients with hyposmia showed a lesser degree of GM reduction, compared with healthy controls. Smaller OB volumes were found for patients with olfactory loss, compared with controls. TBI patients with anosmia had the smallest OB volumes, which were caused by the lesions for OB. In addition, post-TBI duration was negatively correlated with GM density in the secondary olfactory areas in patients with hyposmia, but was positively correlated with GM density in the frontal and temporal gyrus in patients with anosmia. The GM density and OB volume reduction among TBI patients with olfactory loss was largely dependent on the location and severity of brain lesions in olfactory-relevant regions. Longer post-TBI duration had an impact on brain GM density changes, which indicate a decreased olfactory function in patients with hyposmia and possible compensatory mechanisms in patients with anosmia.
Topics: Adult; Aged; Brain Injuries, Traumatic; Female; Gray Matter; Humans; Magnetic Resonance Imaging; Male; Middle Aged; Olfaction Disorders; Olfactory Bulb
PubMed: 29699465
DOI: 10.1089/neu.2017.5393 -
Brain Imaging and Behavior Dec 2018The human sense of smell is closely associated with morphological differences of the fronto-limbic system, specifically the piriform cortex and medial orbitofrontal...
The human sense of smell is closely associated with morphological differences of the fronto-limbic system, specifically the piriform cortex and medial orbitofrontal cortex (mOFC). Still it is unclear whether cortical volume in the core olfactory areas and connected brain regions are shaped differently in individuals who suffer from lifelong olfactory deprivation relative to healthy normosmic individuals. To address this question, we examined if regional variations in gray matter volume were associated with smell ability in seventeen individuals with isolated congenital olfactory impairment (COI) matched with sixteen normosmic controls. All subjects underwent whole-brain magnetic resonance imaging, and voxel-based morphometry was used to estimate regional variations in grey matter volume. The analyses showed that relative to controls, COI subjects had significantly larger grey matter volumes in left middle frontal gyrus and right superior frontal sulcus (SFS). COI subjects with severe olfactory impairment (anosmia) had reduced grey matter volume in the left mOFC and increased volume in right piriform cortex and SFS. Within the COI group olfactory ability, measured with the "Sniffin' Sticks" test, was positively associated with larger grey matter volume in right posterior cingulate and parahippocampal cortices whereas the opposite relationship was observed in controls. Across COI subjects and controls, better olfactory detection threshold was associated with smaller volume in right piriform cortex, while olfactory identification was negatively associated with right SFS volume. Our findings suggest that lifelong olfactory deprivation trigger changes in the cortical volume of prefrontal and limbic brain regions previously linked to olfactory memory.
Topics: Female; Gray Matter; Humans; Image Processing, Computer-Assisted; Limbic System; Magnetic Resonance Imaging; Male; Middle Aged; Olfaction Disorders; Olfactory Perception; Organ Size; Prefrontal Cortex
PubMed: 29442274
DOI: 10.1007/s11682-017-9817-5 -
Neuropsychologia Nov 2022Olfaction, the sense of smell, provides important behavioral functions in many species. The hippocampus (HC) is critical for identifying odors, and hippocampal volume is...
Olfaction, the sense of smell, provides important behavioral functions in many species. The hippocampus (HC) is critical for identifying odors, and hippocampal volume is associated with odor identification ability. Impaired odor identification is often reported in old age and might provide an early marker of cognitive decline and dementia. Here, we explored cross-sectional (n = 225) and longitudinal (n = 118) associations between odor identification ability and hippocampal subfield volumes in a sample of middle-aged and older persons (25-80 years). In older participants, longitudinally decreasing volumes of the hippocampal tail, subiculum, CA4 and the dentate gyrus correlated with changes in odor identification. None of these correlations were observed in younger participants, but there was a significant correlation between longitudinal volume reduction in the tail subfield of the hippocampus and odor identification change across all participants. There were no significant cross-sectional associations between hippocampal subfields and odor identification. These exploratory results provide new information regarding precisely where and when declining HC subfield volumes might be associated with odor identification.
Topics: Middle Aged; Humans; Aged; Smell; Cross-Sectional Studies; Magnetic Resonance Imaging; Hippocampus; Organ Size
PubMed: 36210600
DOI: 10.1016/j.neuropsychologia.2022.108353 -
Experimental Brain Research Nov 1978The possibility that olfactory input is transmitted to specific subregions of the hippocampal formation via the entorhinal cortex was investigated electrophysiologically...
The possibility that olfactory input is transmitted to specific subregions of the hippocampal formation via the entorhinal cortex was investigated electrophysiologically by analyzing the laminar profiles of potentials evoked in the hippocampal formation by stimulation of the lateral olfactory tract (LOT). LOT stimulation resulted in long latency (14--20 ms) evoked responses in the dentate gyrus of the hippocampal formation ipsilateral to the stimulation. The variable long latency of these responses and their inability to follow stimulus rates of 40/s suggested that these potentials reflected polysynaptic activation. Analysis of the laminar profiles of the evoked potentials indicated that the responses originated from a synaptic field localized in the outer portion of the stratum moleculare of the dentate gyrus, a terminal distribution which overlaps that of the lateral entorhinal cortical (LEC) projection to the dentate gyrus. Lesions of the LEC eliminated the long latency responses in the dentate gyrus evoked by LOT stimulation. In addition, a conditioning pulse delivered either to the LOT or to the LEC produced paired pulse potentiation of the response elicited by subsequent stimulation of the other structure. No evidence was found to indicate that responses were generated in regio superior of the hippocampus proper following LOT stimulation. Taken together, these results suggest that stimulation of the LOT activates the dentate gyrus of the hippocampal formation by multisynaptic pathways which relay through the lateral portion of the entorhinal area. This finding is discussed with regard to entorhinal cortical organization and the known olfactory projections to the LEC.
Topics: Animals; Central Nervous System; Cerebral Cortex; Dendrites; Electric Stimulation; Evoked Potentials; Hippocampus; Male; Olfactory Pathways; Rats; Synapses; Synaptic Transmission
PubMed: 215436
DOI: 10.1007/BF00235572 -
Journal of Cellular Physiology Jan 2015In the adult brain, neural progenitor cells (NPCs) reside in the subventricular zone (SVZ) of the lateral ventricles, the dentate gyrus and the olfactory bulb. Following... (Review)
Review
In the adult brain, neural progenitor cells (NPCs) reside in the subventricular zone (SVZ) of the lateral ventricles, the dentate gyrus and the olfactory bulb. Following CNS insult, NPCs from the SVZ can migrate along the rostral migratory stream (RMS), a migration of NPCs that is directed by proinflammatory cytokines. Cells expressing CXCR4 follow a homing signal that ultimately leads to neuronal integration and CNS repair, although such molecules can also promote NPC quiescence. The ligand, SDF1 alpha (or CXCL12) is one of the chemokines secreted at sites of injury that it is known to attract NSC-derived neuroblasts, cells that express CXCR4. In function of its concentration, CXCL12 can induce different responses, promoting NPC migration at low concentrations while favoring cell adhesion via EGF and the alpha 6 integrin at high CXCL12 concentrations. However, the preclinical effectiveness of chemokines and their relationship with NPC mobilization requires further study, particularly with respect to CNS repair. NPC migration may also be affected by the release of cytokines or chemokines induced by local inflammation, through autocrine or paracrine mechanisms, as well as through erythropoietin (EPO) or nitric oxide (NO) release. CXCL12 activity requires G-coupled proteins and the availability of its ligand may be modulated by its binding to CXCR7, for which it shows a stronger affinity than for CXCR4.
Topics: Brain; Cell Adhesion; Cell Differentiation; Cell Movement; Chemokine CXCL12; Dentate Gyrus; Erythropoietin; Humans; Inflammation; Lateral Ventricles; Neural Stem Cells; Neurogenesis; Nitric Oxide; Olfactory Bulb; Protein Binding; Receptors, CXCR; Receptors, CXCR4; Signal Transduction
PubMed: 24913264
DOI: 10.1002/jcp.24695