Lateralisation of nasal cycle is not reflected in the olfactory bulb volumes and cerebral activations.

Nasal cycle (NC) is a rhythmic change of lateralised nasal airflow mediated by the autonomous nervous system. Previous studies reported the dependence of NC dominance or more patent side on handedness and hemispheric cerebral activity. We aimed to investigate firstly the possible lateralised effect of NC on olfactory bulb volume and secondly the association of NC with the lateralised cerebral dominance in terms of olfactory processing. Thirty-five subjects (22 women and 13 men, mean age 26 ± 3 years) participated in the study. NC was ascertained using a portable rhino-flowmeter. Structural and functional brain measurements were assessed using a 3T MR scanner. Vanillin odorant was presented during functional scans using a computer-controlled olfactometer. NC was found to be independent of the olfactory bulb volumes. Also, cerebral activations were found independent of the NC during odorant perception. NC potency is not associated with lateralised structural or functional differences in the cerebral olfactory system.

Neuroimaging the Development of Olfactory Function in a Woman With No Olfactory Bulbs.

This case report describes a woman with lifelong anosmia in her 20s who presented with the acquisition of unpleasant olfactory phantoms.

Functional connectivity patterns in parosmia.

OBJECTIVE: Parosmia is a qualitative olfactory dysfunction presenting as "distorted odor perception" in presence of an odor source. Aim of this study was to use resting state functional connectivity to gain more information on the alteration of olfactory processing at the level of the central nervous system level. METHODS: A cross sectional study was performed in 145 patients with parosmia (age range 20-76 years; 90 women). Presence and degree of parosmia was diagnosed on the basis of standardized questionnaires. Participants also received olfactory testing using the "Sniffin' Sticks". Then they underwent resting state scans using a 3 T magnetic resonance imaging scanner while fixating on a cross. RESULTS: Whole brain analyses revealed reduced functional connectivity in salience as well as executive control networks. Region of interest-based analyses also supported reduced functional connectivity measures between primary and secondary olfactory eloquent areas (temporal pole, supramarginal gyrus and right orbitofrontal cortex; dorso-lateral pre-frontal cortex and the right piriform cortex). CONCLUSIONS: Participants with parosmia exhibited a reduced information flow between memory, decision making centers, and primary and secondary olfactory areas.

Inhalation-modulated detection of olfactory BOLD responses in the human brain.

Introduction: In contrast to other sensory domains, detection of primary olfactory processes using functional magnetic resonance imaging has proven to be notably challenging with conventional block designs. This difficulty arises from significant habituation and hemodynamic responses in olfactory areas that do not appear to align with extended boxcar functions convolved with a generic hemodynamic response model. Consequently, some researchers have advocated for a transition to event-related designs, despite their known lower detection power compared to block designs. Methods: Here, we conducted a block design experiment with 16s of continuous odorant stimulation alternating with 16s of continuous odorless air stimulation in 33 healthy participants. We compared four statistical analyses that relied either on standard block designs (SBD1-2) or on block designs that were modulated by the participants' individual breathing patterns (MBD1-2). Results: We found that such modulated block designs were comparatively more powerful than standard block designs, despite having a substantially lower design efficiency. Using whole-brain effect size maps, we observed that the right insular and medial aspects of the left piriform cortex exhibited a preference for a breathing-modulated analysis approach. Discussion: Research in olfaction that necessitates designs with longer-lasting blocks, such as those employed in the investigation of state-dependent processing, will benefit from the breathing-modulated analyses outlined in this study.

Neural Processing of Odors with Different Well-Being Associations-Findings from Two Consecutive Neuroimaging Studies.

Much is known about the effect of odors on mood, cognition and behavior, but little is known about the relationship between odors and well-being. We investigated the neural processing of odors with different degrees of association with well-being (WB) through two large independent datasets. The study encompassed pre-testing and fMRI. During pre-testing, 100 and 80 (studies 1 and 2) young, healthy subjects participated, rating intensity, valence, and WB association for 14 (study 1) and 8 (study 2) different odors. Pre-testing resulted in the selection of two odors with high WB association (WB-associated) and two odors with lower WB association (neutral odors) for each study. Odors were delivered intranasally to the subjects who underwent fMRI scanning (44 and 41 subjects, respectively, for studies 1 and 2). We assessed brain activity for subjects when they experienced WB-associated versus neutral odors. In study 1, WB-associated odors showed increased activation in the right angular gyrus whereas in study 2, increased activity in the left angular gyrus existed, together with increased activity in the anterior cingulate cortex and posterior orbitofrontal cortex. The increased activity of higher-order cognitive and emotional regions during the processing of WB-associated odors in the two independent studies suggests a role of odors in influencing individual well-being. Moreover, the consistent activation of the angular gyrus might suggest its key role in shifting attention toward relevant emotional stimuli.

Exploring brain functional connectivity in patients with taste loss: a pilot study.

PURPOSE: In a previous neuroimaging study, patients with taste loss showed stronger activations in gustatory cortices compared to people with normal taste function during taste stimulations. The aim of the current study was to examine whether there are changes in central-nervous functional connectivity in patients with taste loss. METHODS: We selected 26 pairs of brain regions related to taste processing as our regions of interests (ROIs). Functional magnetic resonance imaging (fMRI) was used to measure brain responses in seven patients with taste loss and 12 healthy controls as they received taste stimulations (taste condition) and water (water condition). The data were analysed using ROI-to-ROI functional connectivity analysis (FCA). RESULTS: We observed weaker functional connectivity in the patient group between the left and right orbitofrontal cortex in the taste condition and between the left frontal pole and the left superior frontal gyrus in the water condition. CONCLUSION: These results suggested that patients with taste loss experience changes of functional connectivity between brain regions not only relevant to taste processing but also to cognitive functions. While further studies are needed, fMRI might be helpful in diagnosing taste loss as an additional tool in exceptional cases.

Processing of Sweet, Astringent and Pungent Oral Stimuli in the Human Brain.

Taste and oral somatosensation are intimately related to each other from peripheral receptors to the central nervous system. Oral astringent sensation is thought to contain both gustatory and somatosensory components. In the present study, we compared the cerebral response to an astringent stimulus (tannin), with the response to one typical taste stimulus (sweet - sucrose) and one typical somatosensory stimulus (pungent - capsaicin) using functional magnetic resonance imaging (fMRI) of 24 healthy subjects. Three distributed brain sub-regions responded significantly different to the three types of oral stimulations: lobule IX of the cerebellar hemisphere, right dorsolateral superior frontal gyrus, and left middle temporal gyrus. This suggests that these regions play a major role in the discrimination of astringency, taste, and pungency.

Tractography indicates lateralized differences between trigeminal and olfactory pathways.

Odorous sensations are based on trigeminal and olfactory perceptions. Both trigeminal and olfactory stimuli generate overlapping as well as distinctive activations in the olfactory cortex including the piriform cortex. Orbitofrontal cortex (OFC), an integrative center for all senses, is directly activated in the presence of olfactory stimulations. In contrast, the thalamus, a very important midbrain structure, is not directly activated in the presence of odors, but rather acts as a relay for portions of olfactory information between primary olfactory cortex and higher-order processing centers. The aims of the study were (1) to examine the number of streamlines between the piriform cortex and the OFC and also between the piriform cortex and the thalamus and (2) to explore potential correlations between these streamlines and trigeminal and olfactory chemosensory perceptions. Thirty-eight healthy subjects were recruited for the study and underwent diffusion MRI using a 3T MRI scanner with 67 diffusion directions. ROIs were adapted from two studies looking into olfaction in terms of functional and structural properties of the olfactory system. The "waytotal number" was used which corresponds to number of streamlines between two regions of interests. We found the number of streamlines between the piriform cortex and the thalamus to be higher in the left hemisphere, whereas the number of streamlines between the piriform cortex and the OFC were higher in the right hemisphere. We also found streamlines between the piriform cortex and the thalamus to be positively correlated with the intensity of irritating (trigeminal) odors. On the other hand, streamlines between the piriform cortex and the OFC were correlated with the threshold scores for these trigeminal odors. This is the first studying the correlations between streamlines and olfactory scores using tractography. Results suggest that different chemosensory stimuli are processed through different networks in the chemosensory system involving the thalamus.

Subtle Differences in Brain Architecture in Patients with Congenital Anosmia.

People suffering from congenital anosmia show normal brain architecture although they do not have functional sense of smell. Some studies in this regard point to the changes in secondary olfactory cortex, orbitofrontal cortex (OFC), in terms of gray matter volume increase. However, diffusion tensor imaging has not been explored so far. We included 13 congenital anosmia subjects together with 15 controls and looked into various diffusion parameters like FA. Increased FA in bilateral OFC confirms the earlier studies reporting increased gray matter thickness. However, it is quite difficult to interpret FA in terms of gray matter volume. Increased FA has been seen with recovery after traumatic brain injury. Such changes in OFC point to the plastic nature of the brain.

Advancement of PD Is Reflected by White Matter Changes in Olfactory Areas: A Pilot Study.

Loss of sense of smell is a well-known non-motor symptom of Parkinson's disease (PD). Here, we present insight into the association between PD advancement and equivalents of smell loss in olfactory-eloquent brain areas, such as the posterior cortex and orbitofrontal cortex. Twelve PD patients in different Hoehn and Yahr stages and 12 healthy normosmic individuals were examined with diffusion tensor imaging. Tract-based spatial statistics were used to analyze microstructural changes in white matter adjacent to the bilateral posterior and orbitofrontal cortex. Axial diffusivity, mean diffusivity, and radial diffusivity were significantly higher in olfactory ROIs in advanced PD patients. The results of this preliminary study indicate that PD advancement is associated with progressive neurodegeneration in olfactory-related brain areas.

When the Bone Flap Expands Like Bellows of Accordion: Feasibility Study Using Novel Technique of Expansile (Hinge) Craniotomy for Severe Traumatic Brain Injury.

BACKGROUND: Decompressive craniectomy (DC) is a rescue operation performed for reduction of intracranial pressure due to progressive brain swelling, mandating the need for cranioplasty. OBJECTIVE: To describe expansile craniotomy (EC) as a noninferior technique that may be effectively utilized in situations requiring standard DC. MATERIALS AND METHODS: A decision to perform DC or EC was taken by consecutively allocation to either of the procedures. The bone flap was divided into three pieces, which were tied loosely to each other and to the skull using silk threads. The primary outcome included functional assessment using Glasgow outcome scale (GOS) score at 1 year. RESULTS AND CONCLUSIONS: Total 67 patients were included in the analyses, of which, 31 underwent EC and 36 underwent DC. Both the cohorts were matched in terms of baseline determinants for age, Glasgow coma scale, and Rotterdam score at admission. There was no significant difference in GOS scores and the extent of volume expansion obtained by EC as compared to DC. Complication rates though less in EC group did not differ significantly between the groups. EC appears to be the safe and effective alternative to DC in the management of brain swelling due to TBI with a potential to obviate the need of cranioplasty.

Olfactory Modulation of the Contingent Negative Variation to Auditory Stimuli.

Although pleasantness is intrinsically related to the perception of odors it is difficult to objectively assess odor-induced pleasantness. To evaluate the effects of odors of different valences on the contingent negative variation (CNV) in a younger and an older population. Data from 62 participants (27 men, 35 women) were included. Two age groups with Age group 1 (YOUNG) had 30 subjects within age 18-30 years and age group 2 (OLD) had 32 subjects with age >40 years. Pre-testing was performed to acquaint subjects with the experimental tasks and their environment. Subjects received "Sniffin' Sticks" odor identification tests and a standardized medical history to ascertain normosmia. In addition, they also took questionnaires relating to importance of the sense of smell and personality traits. CNV was elicited with two auditory stimuli, S1 followed by S2 at an interval of 2.4 s. Subjects were asked to push a button as fast as possible after they perceived S2. EEG was recorded from 4 positions of the 10-20 system (Fp2, Fz, Cz, and Pz). Four odors plus odorless air was presented in randomized order. The following main results emerged: (1) Consistent with the literature CNV showed a typical topographical distribution with the largest amplitude over the front-central recording sites. (2) 69% of subjects had consistent CNV for all conditions. (3) for some odor conditions CNV amplitudes exhibit a weak relation to odor pleasantness and associations with calmness. (4) CNV amplitude correlated negatively with reaction times. Overall, the results suggest the usefulness of CNV as an electrophysiological measure of cognition. However, in the present context, concomitantly applied odors of different hedonic tones exerted only minor effects on CNV. Thus, we conclude that odors have little or no effect on CNV.

A novel technique for olfactory bulb measurements.

BACKGROUND: To introduce new ways to calculate OB volumes, checking their validity and comparing them to already established technique i.e. OB volumetric based on manual segmentation of OB boundaries. METHODS: Two approaches were used to calculate OB volumes (1) Manual Segmentation using planimetric manual contouring; (2) Box-frame method, calculating the parameters based on a box placed around the OB. RESULTS: We calculated OB volumes using both techniques and found comparable outcomes. High inter-observer reliability was found for volumes calculated by both observers. For manual segmentation, Cronbach's alpha (α) was 0.91 and 0.93 for right and left OB volume, respectively, whereas for the box-frame method α was 0.94 and 0.90 for right and left OB, respectively. CONCLUSIONS: The simple box-frame method of OB volume calculation appears reliable. Its results are comparable to an established technique.

Global study of variability in olfactory sensitivity.

Variability in human olfactory sensitivity has been attributed to individual-level factors such as genetics, age, sex, medical history of infections and trauma, neurogenerative diseases, and emotional disorders. Scarce evidence exists on the cross-cultural variation in olfactory sensitivity. Hence, we performed 2 studies to estimate the variability in olfactory threshold as a function of location and environment. Study 1 involved 11 laboratories from 4 continents (N = 802). In each location, in a designated laboratory, approximately 80 subjects underwent olfactory sensitivity testing with custom-made tests with eucalyptol and phenylethanol (PEA) odors. Tests were based on the Threshold subtest of the Sniffin' Sticks battery. In Study 2, we compared olfactory sensitivity and suprathreshold perception of PEA and eucalyptol in 2 Chinese (N = 160) and 2 Indian (N = 92) populations-one based in their native country and the other in Germany. Both studies present large-scale evidence that olfactory sensitivity varies as a function of geographical location and suggest that environmental factors play an important role in shaping olfactory sensitivity and suprathreshold olfactory perception. We delineate further steps necessary to identify specific factors underlying uncovered variability and the relationship between olfactory sensitivity and suprathreshold odor perception. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Aberrancies of Brain Network Structures in Patients with Anosmia.

Patients with anosmia exhibit structural and functional brain abnormalities. The present study explored changes in brain white matter (WM) in non-neurodegenerative anosmia using diffusion-tensor-based network analysis. Twenty patients with anosmia and sixteen healthy controls were recruited in the cross-sectional, case-control study. Participants underwent olfactory tests (orthonasal and retronasal), neuropsychological assessment (cognitive function and depressive symptoms) and diffusion tensor imaging measurement. Tract-Based Spatial Statistics, graph theoretical analysis and Network-Based Statistics were used to explore the white matter. There was no significant difference in fractional anisotropy (FA) between patients and controls. In global network topological properties comparisons, patients exhibited higher γ and λ levels than controls, and both groups satisfied the criteria of small-world (σ > 1). In local network topological properties, patients had reduced betweenness, degree and efficiency (global and local), as well as increased shortest path length and cluster coefficient in olfactory-related brain areas (anterior cingulum, lenticular nucleus, putamen, hippocampus, amygdala, caudate nucleus, orbito-frontal gyrus). Olfactory threshold scores and the retronasal score were negatively correlated with γ and λ, and the retronasal score was positively correlated with FA values in certain WM tracts, i.e. middle cerebellar peduncle, right inferior cerebellar peduncle, left inferior cerebellar peduncle, right cerebral peduncle, left cerebral peduncle, left cingulum (cingulate gyrus), right cingulum (hippocampus), superior fronto-occipital fasciculus, and, left tapetum. Patients with anosmia demonstrated relevant WM network dysfunction though their structural integrity remained intact. Their retronasal olfaction deficits revealed to be more strongly associated with WM alterations compared with orthonasal olfactory scores.

Brachial plexus injury and resting-state fMRI: Need for consensus.

OBJECTIVE: The purpose of the study is to conduct the systematic review of literature available on resting-state functional MRI (fMRI) and brachial plexus injury. METHODS: We reviewed all the literature that are available on PubMed; keywords used were resting state, brachial plexus injury, and functional imaging. The reference papers listed were also reviewed. The research items were restricted to publications in English. Some papers have also incorporated studies such as task-based fMRI and transcranial magnetic stimulation (TMS), but only resting-state studies were included for this review. RESULTS: A total of 13 papers were identified, and only 10 were reviewed based on the criteria. The reviewed papers were further categorized on the basis of whether or not any surgical intervention was done. Seven papers have surgical management such as contralateral cervical 7 (CC7) neurotisation or intercostal nerve (ICN) musculocutaneous nerve (MCN) neurotisation. CONCLUSION: There is conclusive evidence showing that there is cortical reorganisation following brachial plexus injury in both birth and traumatic cases. The changes are restricted to some of the resting-state networks only (default mode network, sensorimotor network, in particular). However, no study till date has focused on a far more longitudinal approach at studying these changes. It will be interesting to see the exact time and effect of these changes.

Individual differences in trait anxiety are associated with gray matter alterations in hypothalamus: Preliminary neuroanatomical evidence.

Trait anxiety is particularly a prone phenotype for the development of anxiety disorders and depression. Studying the neural underpinnings of trait anxiety can further inform our understanding of the etiology of these disorders. To investigate the structural correlates of trait anxiety, high resolution structural images were acquired from 76 right-handed healthy participants and gray matter volumes were extracted from a priori regions of interest (ROIs) that were earlier implicated in anxiety like behaviour (i.e., hippocampus, amygdala, anterior cingulate cortex, thalamus, hypothalamus and prefrontal (dorsolateral, rostrolateral, ventrolateral) cortex. In a partial correlation analysis (with age, gender, and Beck Depression Inventory (BDI) scores as covariates of no interest), trait anxiety was found to be negatively correlated with the gray matter volume of hypothalamus bilaterally and positively correlated with the gray matter volume of left thalamus. In a hierarchical multiple regression analysis, grey matter volume of hypothalamus and left thalamus were found to be the significant predictors of trait anxiety. Our findings thus suggest that a smaller gray matter volume in the hypothalamus and an increase in the gray matter volume of left thalamus is related to a disposition to high anxiety personality trait.