Plasticity of the human olfactory system: the olfactory bulb

Addressing flavor challenges in reduced-fat dairy products: A review from the perspective of flavor compounds and their improvement strategies

In recent years, the demand for reduced-fat dairy products (RFDPs) has increased rapidly as the health risks associated with high-fat diets have become increasingly apparent. Unfortunately, lowering the fat content in dairy products would reduce the flavor perception of fat. Fat-derived flavor compounds are the main contributor to appealing flavor among dairy products. However, the contribution of fat-derived flavor compounds remains underappreciated among the flavor improvement factors of RFDPs. Therefore, this review aims to summarize the flavor perception mechanism of fat and the profile of fat-derived flavor compounds in dairy products. Furthermore, the characteristics and influencing factors of flavor compound release are discussed. Based on the role of these flavor compounds, this review analyzed the current and potential flavor improvement strategies for RFDPs, including physical processing, lipolysis, microbial applications, and fat replacement. Overall, promoting the synthesis of milk fat characteristic flavor compounds in RFDPs and aligning the release properties of flavor compounds from the RFDPs with those of equivalent full-fat dairy products are two core strategies to improve the flavor of reduced-fat dairy products. In the future, better modulation of the behavior of flavor compounds by various methods is promising to replicate the flavor properties of fat in RFDPs and meet consumer sensory demands.

The olfactory bulb: A neuroendocrine spotlight on feeding and metabolism

Olfaction is the most ancient sense and is needed for food-seeking, danger protection, mating and survival. It is often the first sensory modality to perceive changes in the external environment, before sight, taste or sound. Odour molecules activate olfactory sensory neurons that reside on the olfactory epithelium in the nasal cavity, which transmits this odour-specific information to the olfactory bulb (OB), where it is relayed to higher brain regions involved in olfactory perception and behaviour. Besides odour processing, recent studies suggest that the OB extends its function into the regulation of food intake and energy balance. Furthermore, numerous hormone receptors associated with appetite and metabolism are expressed within the OB, suggesting a neuroendocrine role outside the hypothalamus. Olfactory cues are important to promote food preparatory behaviours and consumption, such as enhancing appetite and salivation. In addition, altered metabolism or energy state (fasting, satiety and overnutrition) can change olfactory processing and perception. Similarly, various animal models and human pathologies indicate a strong link between olfactory impairment and metabolic dysfunction. Therefore, understanding the nature of this reciprocal relationship is critical to understand how olfactory or metabolic disorders arise. This present review elaborates on the connection between olfaction, feeding behaviour and metabolism and will shed light on the neuroendocrine role of the OB as an interface between the external and internal environments. Elucidating the specific mechanisms by which olfactory signals are integrated and translated into metabolic responses holds promise for the development of targeted therapeutic strategies and interventions aimed at modulating appetite and promoting metabolic health.

Recall of Autobiographical Memories Following Odor vs Verbal Cues Among Adults With Major Depressive Disorder

Importance

Major depressive disorder (MDD) is associated with deficits in autobiographical memory (AM) recall, which is thought to stem from disruptions in effortful recall. Understanding whether these deficits are mitigated when recall is stimulated more directly, such as by odor cues, could inform therapeutic interventions for MDD.

Objective

To evaluate whether deficits in specific AM recall in MDD are mitigated when odor cues vs word cues are used to prompt memory.

Design, Setting, and Participants

This cross-sectional study assessed recall of specific AMs in response to both odor cues and word cues (in a randomized, counterbalanced order) in a repeated measures design. Data were collected between September 2021 and November 2022. The study took place at the University of Pittsburgh School of Medicine in Pennsylvania and included adults with a primary diagnosis of MDD, according to the Mini International Neuropsychiatric Interview. Data were analyzed from January to June 2023.

Main Outcomes and Measures

The primary outcome measure was the percentage of specific AMs recalled in response to odor-cued memories vs word-cued memories. Additional outcome measures included ratings of arousal, vividness, repetition, and recall response time for odor-cued memories vs word-cued memories.

Results

Thirty-two adults (mean [SD] age, 30.0 [10.1] years; 26 [81.3%] female; 6 [18.8%] male) with a primary diagnosis of MDD completed the study. Participants recalled more specific AMs for odor cues than word cues (mean [SD], 68.4% [20.4%] vs 52.1% [23.3%]; Cohen d, 0.78; P < .001). Additionally, odor-cued recall was rated more arousing (mean [SD], 3.0 [0.8] vs 2.6 [0.7]; Cohen d, 1.28; P < .001) and vivid (mean [SD], 3.3 [0.7] vs 3.0 [0.7]; Cohen d, 0.67; P < .001), and was slower than word-cued recall (mean [SD], 14.5 [3.6] vs 8.9 [3.4] seconds; Cohen d, 1.18; P < .001). When compared with the population mean for word cues in healthy controls (80%), participants recalled fewer specific memories in response to words (Cohen d, 1.18; P < .001), supporting the presence of overgenerality. Notably, the percentage of specific memories recalled in response to odor cues did not differ from the healthy control population mean (Cohen d, 0.26; P = .15).

Conclusions and Relevance

In this cross-sectional study, adults with MDD recalled more specific AMs in response to odor cues compared with word cues. This study suggests that AM deficits may only be observed when verbal cues are used and provides a potential new method for increasing specific AM recall in patients with MDD.

Primary and secondary olfactory centres in human ontogeny

The olfactory centres are the evolutionary oldest and most conservative area of the telencephalon. Olfactory deficiencies are involved in a large spectrum of neurologic disorders and neurodegenerative diseases. The growing interest in human olfaction has been also been driven by COVID-19-induced transitional anosmia. Nevertheless, recent data on the human olfactory centres concerning normal histology and morphogenesis are rare. Published data in the field are mainly restricted to classic studies with non-uniform nomenclature and varied definitions of certain olfactory areas. While the olfactory system in model animals (rats, mice, and more rarely non-human primates) has been extensively investigated, the developmental timetable of olfactory centres in both human prenatal and postnatal ontogeny are poorly understood and unsystemised, which complicates the process of analysing human material, including medical researches. The main purpose of this review is to provide and discuss relevant morphological data on the normal ontogeny of the human olfactory centres, with a focus on the timetable of maturation and developmental cytoarchitecture, and with special reference to the definitions and terminology of certain olfactory areas.

The Olfactory Bulb in Companion Animals-Anatomy, Physiology, and Clinical Importance

The Olfactory Bulb is a component of the Olfactory System, in which it plays an essential role as an interface between the peripheral components and the cerebral cortex responsible for olfactory interpretation and discrimination. It is in this element that the first selective integration of olfactory stimuli occurs through a complex cell interaction that forwards the received olfactory information to higher cortical centers. Considering its position in the organizational hierarchy of the olfactory system, it is now known that changes in the Olfactory Bulb can lead to olfactory abnormalities. Through imaging techniques, it was possible to establish relationships between the occurrence of changes secondary to brain aging and senility, neurodegenerative diseases, head trauma, and infectious diseases with a decrease in the size of the Olfactory Bulb and in olfactory acuity. In companion animals, this relationship has also been identified, with observations of relations between the cranial conformation, the disposition, size, and shape of the Olfactory Bulb, and the occurrence of structural alterations associated with diseases with different etiologies. However, greater difficulty in quantitatively assessing olfactory acuity in animals and a manifestly smaller number of studies dedicated to this topic maintain a lack of concrete and unequivocal results in this field of veterinary sciences. The aim of this work is to revisit the Olfactory Bulb in companion animals in all its dimensions, review its anatomy and histological characteristics, physiological integration in the olfactory system, importance as a potential early indicator of the establishment of specific pathologies, as well as techniques of imaging evaluation for its in vivo clinical exploration.

Surgical Approaches for Possible Positions of an Olfactory Implant to Stimulate the Olfactory Bulb

INTRODUCTION

Current scientific developments seem to allow for an "olfactory implant" in analogy to cochlear implants. However, the position and surgical approaches for electrical stimulation of the olfactory system are unclear.

METHODS

In a human anatomic cadaver study, we investigated different endoscopic approaches to electrically stimulate the olfactory bulb (OB) based on the following considerations: (1) the stimulating electrode should be close to the OB. (2) The surgical procedure should be as non-invasive and safe as possible and (3) as easy as possible for an experienced ENT surgeon.

RESULTS

In summary, the endoscopic intracranial positioning of the electrode via a widened ostium of the fila olfactoria or a frontal sinus surgery like a Draf IIb procedure is a good option in terms of patients' risk, degree of difficulty for ENT surgeons, and position to the OB. Endoscopic intranasal positioning appeared to be the best option in terms of patient risk and the degree of difficulty for ENT surgeons. Although a bigger approach to the OB using a drill and the combined intranasal endoscopic and external approach enabled a close placement of the electrode to the OB, they do not seem relevant in practice due to their higher invasiveness.

CONCLUSION

The study suggested that an intranasal positioning of a stimulating electrode is possible, with placements beneath the cribriform plate, extra- or intracranially, applying elegant surgical techniques with low or medium risk to the patient and a close placement to OB.

Liu D, A. Müller C, A. Stuck B, Welge-Lüssen A, Hähner A. Olfactory Dysfunction: Etiology, Diagnosis, and Treatment

BACKGROUND

Disorders of the sense of smell have received greater attention because of the frequency with which they occur as a symptom of SARS-CoV-2 infection. Olfactory dysfunction can lead to profound reduction in quality of life and may arise from many different causes.

METHODS

A selective literature review was conducted with consideration of the current version of the guideline issued by the Association of the Scientific Medical Societies in Germany.

RESULTS

The cornerstones of diagnosis are the relevant medical history and psychophysical testing of olfactory function using standardized validated tests. Modern treatment strategies are oriented on the cause of the dysfunction. While treatment of the underlying inflammation takes precedence in patients with sinunasal dysosmia, olfactory training is the primary treatment option for other forms of the disorder. The prognosis is determined not only by the cause of the olfactory dysfunction and the patient's age, but also by the olfactory performance as measured at the time of diagnosis.

CONCLUSION

Options for the treatment of olfactory dysfunction are available but limited, depending on the cause. It is therefore important to carry out a detailed diagnostic work-up and keep the patient informed of the expected course and prognosis.

Olfaction in (Social) Context: The Role of Social Complexity in Trajectories of Older Adults' Olfactory Abilities

Objectives: Olfaction is an important correlate of later-life health, including cognition and mortality risk. Environmental enrichment protects against olfactory decline, yet little research considers the social context as a source of sensory enrichment or stimulation. This study examines how exposure to social complexity (i.e., diversity or novelty in social networks and activities) shapes later-life olfaction. Methods: Cross-sectional and longitudinal ordered logit models analyze data from 1,447 older adults interviewed at Rounds 1 and 2 of the National Social Life, Health, and Aging Project. Results: Exposure to greater social complexity (larger social networks, greater network diversity) is associated with significantly better olfaction at baseline. Increases in network diversity and fewer network losses significantly protect against olfactory decline over time. Discussion: Findings highlight the social context as an important, yet relatively overlooked source of sensory enrichment, and underscore the need for biological applications to integrate social life dynamics into studies of health trajectories.

Gestational diabetes mellitus increased the number of dopaminergic neurons in the olfactory bulb of rat offspring

Objectives

Gestational Diabetes Mellitus (GDM) is the most common metabolic complication of pregnancy that causes central nervous system and olfactory dysfunction in the offspring. It has been demonstrated that dopamine modulates several aspects of olfactory information processing in vertebrates.

Materials and Methods

In this study, we investigated the effect of gestational diabetes on the expression of the Dopamine (DA) metabolism genes, tyrosine hydroxylase (TH), and dopa decarboxylase (DDC) in the olfactory bulb (OB) tissue of rats' offspring. Female Wistar rats were divided into a control group which received citrate buffer and the diabetic group which received 45 mg/kg of streptozotocin (STZ) on day 0 of gestation. Fasting blood glucose levels were measured before and 72 hr after injection. OB tissues of adult offspring were isolated, and TH-positive cells were counted by immunofluorescence staining. Also, TH and DDC expressions were analyzed by qRT- PCR and western blot.

Results

The data showed that gestational diabetes could cause up-regulation of TH (P<0.01) and DDC (P<0.05) in the OB tissue of offspring. Furthermore, our results showed that GDM causes a significant increase in TH and DDC protein levels in the OB tissues of offspring. Immunohistochemistry showed a significant increase in the number of TH-positive cells in the offspring of diabetic mothers (P<0.05).

Conclusion

This study showed that gestational diabetes could cause an increase in TH and DDC gene expression in the OB tissue in the offspring, which may be correlated with reduced olfactory sensitivity.

Investigations and Outcomes for Olfactory Disorders

Purpose of Review

To provide a detailed overview of the investigations and core outcome measures for olfactory disorders.

Recent Findings

Olfactory disorders can have a detrimental impact to the quality of life of patients. There are a wide range of causes of olfactory loss including sinonasal conditions, idiopathic, post-head trauma or infection. This review highlights the key investigations and reasoning for their use to clinically assess and research patients with olfactory disorders. In addition, this review outlines the core outcome measures for olfaction that will help inform future research in olfactory disorders.

Summary

A systematic approach with history taking and examination particularly with nasal endoscopy can determine the cause of the olfactory disorder in most cases. Specific olfactory disorder questionnaires can demonstrate the impact on quality of life, while psychophysical testing can objectively assess and monitor olfaction over time. Olfactory-evoked potentials and functional MRI are reserved for research, whereas CT and MRI imaging are used depending on history and examination. A core outcome set for olfaction has been developed that will help standardise the outcome measures used in olfaction and olfactory disorders research.

Research Progress of Olfactory Nerve Regeneration Mechanism and Olfactory Training

The olfactory nerve (ON) is the only cranial nerve exposed to the external environment. Hence, it is susceptible to damage from head trauma, viral infection, inflammatory stimulation, and chemical toxins, which can lead to olfactory dysfunction. However, compared with all other cranial nerves, the ON is unique due to its inherent ability to regenerate. This characteristic provides a theoretical basis for treatment of olfactory dysfunction. Olfactory training (OT) is one of the main treatments for olfactory dysfunction. It is easy to apply and has few side-effects, and has been shown to be efficacious for patients with olfactory dysfunction of various causes. To further understand the application value of ON regeneration and OT on olfactory dysfunction, we review the research progress on the mechanism of ON regeneration and OT.

Olfactory bulb volume and cortical thickness evolve during sommelier training

Brain plasticity is essential for experts to acquire the abilities they need. Sommeliers are olfaction experts who display differences in olfactory regions in the brain that correlate with greater olfactory abilities. While most studies on this topic are cross‐sectional, we used a longitudinal design and invited 17 sommelier students at the start and end of their training then to compare them to 17 control students to study the effects of training‐related brain plasticity. After a year and a half, 5 sommelier students and 4 control students dropped out, leading to 12 sommelier students versus 13 controls. We used magnetic resonance imaging to measure cortical thickness and olfactory bulb volume, as this structure plays a crucial role in olfactory processing. We used the Sniffin' Sticks test to evaluate olfactory performance. During training, olfactory bulb volume increased in sommelier students while there was no significant change in the control group. We also observed that thickness of right entorhinal cortex increased, and cortical thickness decreased in other cerebral regions. Our olfactory tests did not reveal any significant changes in sommelier students. In conclusion, this is the first longitudinal study to report an increase in olfactory bulb volume in olfaction experts in line with the notion of effects of ecological training‐related brain plasticity. The mixed results about cortical thickness might be explained by a “overproduction‐pruning” model of brain plasticity, according to which the effects of training‐related plasticity are non‐linear and simultaneously involve different processes.

Neural circuits of anxiolytic and antidepressant pherine molecules

In this review, we describe proposed circuits mediating the mechanism of action of pherines, a new class of synthetic neuroactive steroids with demonstrated antianxiety and antidepressant properties, that engage nasal chemosensory receptors. We hypothesize that afferent signals triggered by activation of these peripheral receptors could reach subgroups of olfactory bulb neurons broadcasting information to gamma-aminobutyric acid (GABAergic) and corticotropin-releasing hormone (CRH) neurons in the limbic amygdala. We propose that chemosensory inputs triggered by pherines project to centrolateral (CeL) and centromedial (CeM) amygdala neurons, with downstream effects mediating behavioral actions. Anxiolytic pherines could activate the forward inhibitory GABAergic neurons that facilitate the release of neuropeptide S (NPS) in the locus coeruleus (LC) and GABA in the bed nucleus of the stria terminalis (BNST) and inhibit catecholamine release in the LC and ventral tegmental area (VTA) leading to rapid anxiolytic effect. Alternatively, antidepressant pherines could facilitate the CRH and GABAergic neurons that inhibit the release of NPS from the LC, increase glutamate release from the BNST, and increase norepinephrine (NE), dopamine (DA), and serotonin release from the LC, VTA, and raphe nucleus, respectively. Activation of these neural circuits leads to rapid antidepressant effect. The information provided is consistent with this model, but it should be noted that some steps on these pathways have not been demonstrated conclusively in the human brain.

The Shape of the Olfactory Bulb Predicts Olfactory Function

The olfactory bulb (OB) plays a key role in the processing of olfactory information. A large body of research has shown that OB volumes correlate with olfactory function, which provides diagnostic and prognostic information in olfactory dysfunction. Still, the potential value of the OB shape remains unclear. Based on our clinical experience we hypothesized that the shape of the OB predicts olfactory function, and that it is linked to olfactory loss, age, and gender. The aim of this study was to produce a classification of OB shape in the human brain, scalable to clinical and research applications. Results from patients with the five most frequent causes of olfactory dysfunction (n = 192) as well as age/gender-matched healthy controls (n = 77) were included. Olfactory function was examined in great detail using the extended “Sniffin’ Sticks” test. A high-resolution structural T2-weighted MRI scan was obtained for all. The planimetric contours (surface in mm²) of OB were delineated manually, and then all surfaces were added and multiplied to obtain the OB volume in mm³. OB shapes were outlined manually and characterized on a selected slice through the posterior coronal plane tangential to the eyeballs. We looked at OB shapes in terms of convexity and defined two patterns/seven categories based on OB contours: convex (olive, circle, and plano-convex) and non-convex (banana, irregular, plane, and scattered). Categorization of OB shapes is possible with a substantial inter-rater agreement (Cohen’s Kappa = 0.73). Our results suggested that non-convex OB patterns were significantly more often observed in patients than in controls. OB shapes were correlated with olfactory function in the whole group, independent of age, gender, and OB volume. OB shapes seemed to change with age in healthy subjects. Importantly, the results indicated that OB shapes were associated with certain causes of olfactory disorders, i.e., an irregular OB shape was significantly more often observed in post-traumatic olfactory loss. Our study provides evidence that the shape of the OB can be used as a biomarker for olfactory dysfunction.

Unilateral Choanal Atresia: Indications of Long-Term Olfactory Deficits and Volumetric Brain Changes Postsurgically

BACKGROUND

Very few studies have investigated whether unilateral choanal atresia is associated with permanent olfactory deficits.

OBJECTIVE

This study aimed to evaluate the olfactory performance of patients with unilateral choanal atresia postsurgically.

METHODS

Three patients with unilateral atresia were examined in terms of olfactory performance with the Sniffin' Sticks test (odor identification, threshold, and discrimination), size of the olfactory bulb, and volumetric brain changes.

RESULTS

All patients demonstrated significantly lower olfactory performance in terms of odor threshold on the same side with the choanal atresia. Grey matter reductions were found ipsilaterally in the hippocampus.

CONCLUSIONS

This pilot study indicates that persistent olfactory deficits and volumetric brain changes are present in patients with unilateral choanal atresia.

Smell Regions in Patients with Vitamin D Deficiency: An MRI Evaluation

Objective  We investigated the effects of vitamin D deficiency in the peripheral and central smell regions by magnetic resonance imaging (MRI). Methods  This retrospective study included 29 patients (12 males, 17 females) with 25-dihydroxy vitamin D3 [25(OH) ₂ D ₃ ] deficiency (group 1) and 34 subjects without 25(OH) ₂ D ₃ deficiency (14 males, 20 females) (group 2). Using cranial MRIs, the peripheral (olfactory bulb [OB] volume and olfactory sulcus [OS] depth) and central (insular gyrus and corpus amygdala) smell regions were evaluated. Results  The OB volume and OS depth values of the 25(OH) ₂ D3 deficiency group were significantly lower than those of the control group ( p  < 0.05). For the central smell regions, the insular gyrus and corpus amygdala areas of the 25(OH) ₂ D3 deficiency group were nonsignificantly lower than those in the control group ( p  > 0.05). There were positive correlations between OB volumes, OS depths, and insular gyrus and corpus amygdala areas bilaterally in the 25(OH) ₂ D3 deficiency group separately and in all subjects (groups 1 and 2) ( p  < 0.05). In the 25(OH) ₂ D3 deficiency group, as the 25(OH) ₂ D3 values became lower, the insular gyrus area values decreased bilaterally ( p  < 0.05). In females, the corpus amygdala area values were lower than in males ( p  < 0.05). Conclusion  Since vitamin D3 deficiency affected the peripheral and central smell regions negatively, we recommend evaluating patients' vitamin D levels as a health policy to prevent vitamin D3 deficiency-related cranial smell region problems. Moreover, sunlight exposure is very important to increase vitamin D levels, and the public should be informed about this topic.

Automatic Segmentation of the Olfactory Bulb

The olfactory bulb (OB) has an essential role in the human olfactory pathway. A change in olfactory function is associated with a change of OB volume. It has been shown to predict the prognosis of olfactory loss and its volume is a biomarker for various neurodegenerative diseases, such as Alzheimer’s disease. Thus far, obtaining an OB volume for research purposes has been performed by manual segmentation alone; a very time-consuming and highly rater-biased process. As such, this process dramatically reduces the ability to produce fair and reliable comparisons between studies, as well as the processing of large datasets. Our study aims to solve this by proposing a novel methodological framework for the unbiased measurement of OB volume. In this paper, we present a fully automated tool that successfully performs such a task, accurately and quickly. In order to develop a stable and versatile algorithm and to train the neural network, we used four datasets consisting of whole-brain T1 and high-resolution T2 MRI scans, as well as the corresponding clinical information of the subject’s smelling ability. One dataset contained data of patients suffering from anosmia or hyposmia (N = 79), and the other three datasets contained data of healthy controls (N = 91). First, the manual segmentation labels of the OBs were created by two experienced raters, independently and blinded. The algorithm consisted of the following four different steps: (1) multimodal data co-registration of whole-brain T1 images and T2 images, (2) template-based localization of OBs, (3) bounding box construction, and lastly, (4) segmentation of the OB using a 3D-U-Net. The results from the automated segmentation algorithm were tested on previously unseen data, achieving a mean dice coefficient (DC) of 0.77 ± 0.05, which is remarkably convergent with the inter-rater DC of 0.79 ± 0.08 estimated for the same cohort. Additionally, the symmetric surface distance (ASSD) was 0.43 ± 0.10. Furthermore, the segmentations produced using our algorithm were manually rated by an independent blinded rater and have reached an equivalent rating score of 5.95 ± 0.87 compared to a rating score of 6.23 ± 0.87 for the first rater’s segmentation and 5.92 ± 0.81 for the second rater’s manual segmentation. Taken together, these results support the success of our tool in producing automatic fast (3–5 min per subject) and reliable segmentations of the OB, with virtually matching accuracy with the current gold standard technique for OB segmentation. In conclusion, we present a newly developed ready-to-use tool that can perform the segmentation of OBs based on multimodal data consisting of T1 whole-brain images and T2 coronal high-resolution images. The accuracy of the segmentations predicted by the algorithm matches the manual segmentations made by two well-experienced raters. This method holds potential for immediate implementation in clinical practice. Furthermore, its ability to perform quick and accurate processing of large datasets may provide a valuable contribution to advancing our knowledge of the olfactory system, in health and disease. Specifically, our framework may integrate the use of olfactory bulb volume (OBV) measurements for the diagnosis and treatment of olfactory loss and improve the prognosis and treatment options of olfactory dysfunctions.

Sinonasal surgery alters brain structure and function: Neuroanatomical correlates of olfactory dysfunction

Olfactory dysfunction (OD) is more common than hearing loss, partial blindness, or blindness and can have a significant impact on the quality of life. Moreover, unexplained OD is an early biomarker in neurodegenerative diseases and increases 5-year mortality risk. Structural alterations in olfactory eloquent brain regions may represent the neuroanatomical correlates of OD. Previous studies have demonstrated reduced gray matter (GM) volume in areas of presumed olfactory relevance in patients with OD. However, being cross-sectional in nature, these studies do not provide evidence of causality, for which longitudinal work is required. At present, however, longitudinal studies addressing olfactory structural plasticity are limited, both in number and methodological approach: to our knowledge, such work has not included parallel functional imaging to confirm the relevance of structural change. We therefore performed a longitudinal multimodal neuroimaging study investigating structural and functional plasticity in 24 patients undergoing surgical treatment for chronic rhinosinusitis, compared with 17 healthy controls. We demonstrated functionally significant structural plasticity within the orbitofrontal, anterior cingulate and insular cortices, and temporal poles in patients 3 months after surgery. Of interest, GM volume decreased in these regions, in association with increased psychophysical scores and BOLD signal. To our knowledge, this is the first study to demonstrate both structural and functional plasticity of the central olfactory networks, thereby confirming these areas as neuroanatomical correlates of olfactory function/dysfunction.

Better Olfactory Performance and Larger Olfactory Bulbs in a Mouse Model of Congenital Blindness

It is well established that early blindness results in enhancement of the remaining nonvisual sensory modalities accompanied by functional and anatomical brain plasticity. While auditory and tactile functions have been largely investigated, the results regarding olfactory functions remained less explored and less consistent. In the present study, we investigated olfactory function in blind mice using 3 tests: the buried food test, the olfactory threshold test, and the olfactory performance test. The results indicated better performance of blind mice in the buried food test and odor performance test while there was no difference in the olfactory threshold test. Using histological measurements, we also investigated if there was anatomical plasticity in the olfactory bulbs (OB), the most salient site for olfactory processing. The results indicated a larger volume of the OB driven by larger glomerular and granular layers in blind mice compared with sighted mice. Structural plasticity in the OB may underlie the enhanced olfactory performance in blind mice.

Application of adverse outcome pathway networks to integrate mechanistic data informing the choice of a point of departure for hydrogen sulfide exposure limits

Acute exposure to hydrogen sulfide initiates a series of hallmark biological effects that occur progressively at increasing exposure levels: odor perception, conjunctivitis, olfactory paralysis, "knockdown," pulmonary edema, and apnea. Although effects of exposure to high concentrations of hydrogen sulfide are clear, effects associated with chronic, low-level exposure in humans is under debate, leading to uncertainty in the critical effect used in regulatory risk assessments addressing low dose exposures. This study integrates experimental animal, observational epidemiology, and occupational exposure evidence by applying a pathway-based approach. A hypothesized adverse outcome pathway (AOP) network was developed from 34 studies, composed of 4 AOPs sharing 1 molecular initiating events (MIE) and culminating in 4 adverse outcomes. A comparative assessment of effect levels and weight of evidence identified an AOP leading to a biologically-plausible, low-dose outcome relative to the other outcomes (nasal lesions, 30 ppm versus olfactory paralysis, >100 ppm; neurological effects, >80 ppm; pulmonary edema, >80 ppm). This AOP (i.e. AOP1) consists of the following key events: cytochrome oxidase inhibition (>10 ppm), neuronal cell loss (>30 ppm), and olfactory nasal lesions (defined as both neuronal cell loss and basal cell hyperplasia; >30 ppm) in rodents. The key event relationships in this pathway were supported by moderate empirical evidence and have high biological plausibility due to known mechanistic understanding and consistency in observations for diverse chemicals.

Radiological evidence to changes in the olfactory bulb volume depending on body mass index in the childhood

OBJECTIVE

Energy balance is preserved through the exchange between body weight and adipose tissue across the multi-faceted complex network that is composed of the sensorial, metabolic, and neuro-endocrine circuits. The olfactory control of energy homeostasis is maintained through the interplay between the olfactory bulb (OB) and adipose tissue. While extremely studied, most researches still report controversial results and sensorial regulation of obesity is not fully understood. This study aims to investigate the interplay between olfactory bulb volume (OBV) as a radiological clue of sensorial control and obesity in children.

SUBJECTS AND METHOD

Children (n = 195) were classified into four groups based on body mass index (BMI) percentiles: normal weight (n = 89), overweight (n = 31), obese (n = 32) and morbidly obese (n = 43). OBV were calculated using MRI.

RESULTS

Mean OBV was higher in children with obesity than in those of normal weights. The means of OBV are found higher in the overweight and obese children (43.76 ± 9.50-49.29 ± 8.61 mm³) than in those of morbidly obese (38.23 ± 11.52 mm³) (p < 0.001). In overweight and obese children, a positive correlation were found between the BMI and OBV (r_overweigh = 0.275-r_obese = 0.377), while in the morbidly obese group, there was a negative correlation (r_{severelyobese} = -0.445).

CONCLUSION

This study reveals that OBV is higher in obese children. Also, it shows that there is a positive correlation between OBV and BMI in overweight and obese children and a negative correlation in the morbidly obese group. These radiological bimodal changes in OBV indicate that olfactory control acts to provide energy balance, mediated by positive in the overweight and obese children, negative feedback in the morbidly obese group.

Olfactory bulb surroundings can help to distinguish Parkinson's disease from non-parkinsonian olfactory dysfunction

BACKGROUND

The olfactory bulb is one of the first regions of insult in Parkinson's disease (PD), consistent with the early onset of olfactory dysfunction. Investigations of the olfactory bulb may, therefore, help early pre-motor diagnosis. We aimed to investigate olfactory bulb and its surrounding regions in PD-related olfactory dysfunction when specifically compared to other forms of non-parkinsonian olfactory dysfunction (NPOD) and healthy controls.

METHODS

We carried out MRI-based olfactory bulb volume measurements from T2-weighted imaging in scans from 15 patients diagnosed with PD, 15 patients with either post-viral or sinonasal NPOD and 15 control participants. Further, we applied a deep learning model (convolutional neural network; CNN) to scans of the olfactory bulb and its surrounding area to classify PD-related scans from NPOD-related scans.

RESULTS

Compared to controls, both PD and NPOD patients had smaller olfactory bulbs, when measured manually (both p < .001) whereas no difference was found between PD and NPOD patients. In contrast, when a CNN was used to differentiate between PD patients and NPOD patients, an accuracy of 88.3% was achieved. The cortical area above the olfactory bulb which stretches around and into the olfactory sulcus appears to be a region of interest in the differentiation between PD and NPOD patients.

CONCLUSION

Measures from and around the olfactory bulb in combination with the use of a deep learning model may help differentiate PD patients from patients with NPOD, which may be used to develop early diagnostic tools based on olfactory dysfunction.

Thallium-201 Imaging in Intact Olfactory Sensory Neurons with Reduced Pre-Synaptic Inhibition In Vivo

In this study, we determined whether the ²⁰¹Tl (thallium-201)-based olfactory imaging is affected if olfactory sensory neurons received reduced pre-synaptic inhibition signals from dopaminergic interneurons in the olfactory bulb in vivo. The thallium-201 migration rate to the olfactory bulb and the number of action potentials of olfactory sensory neurons were assessed 3 h following left side nasal administration of rotenone, a mitochondrial respiratory chain complex I inhibitor that decreases the number of dopaminergic interneurons without damaging the olfactory sensory neurons in the olfactory bulb, in mice (6–7 animals per group). The migration rate of thallium-201 to the olfactory bulb was significantly increased following intranasal administration of thallium-201 and rotenone (10 μg rotenone, p = 0.0012; 20 μg rotenone, p = 0.0012), compared with that in control mice. The number of action potentials was significantly reduced in the olfactory sensory neurons in the rotenone treated side of 20 μg rotenone-treated mice, compared with that in control mice (p = 0.0029). The migration rate of thallium-201 to the olfactory bulb assessed with SPECT-CT was significantly increased in rats 24 h after the left intranasal administration of thallium-201 and 100 μg rotenone, compared with that in control rats (p = 0.008, 5 rats per group). Our results suggest that thallium-201 migration to the olfactory bulb is increased in intact olfactory sensory neurons with reduced pre-synaptic inhibition from dopaminergic interneurons in olfactory bulb glomeruli.

Individual variability of olfactory fMRI in normosmia and olfactory dysfunction

Purpose

The diagnosis of olfactory dysfunction is mainly based on psychophysical measurements. The aim of the current study was to investigate how well the olfactory functional magnetic resonance imaging (fMRI) can effectively distinguish between normosmic people and subjects with olfactory dysfunction.

Methods

Thirty-eight participants were recruited for the study. Group 1 consisted of 22 subjects with olfactory dysfunction (mean age = 44.3 years, SD = 18.6), and Group two consisted of 16 participants with normal olfactory function (mean age = 49.6 years, SD = 11.6). Olfactory functions were assessed in great detail for all participants, and brain activation in response to odorous stimulation was assessed using fMRI.

Results

The between-group comparison showed stronger odor induced brain activation of the primary olfactory area and the insular cortex among the normosmic group as compared to the dysosmic group. As indicated by the individual analysis, positive responses in the primary olfactory cortex were significantly higher in normosmic people (94%) than in subjects with olfactory dysfunction (41%). However, there was no association between individual fMRI parameters (including the percentage of BOLD signal change, activated cluster size and peak z value), and psychophysical olfactory test scores. Receiver operating characteristic analysis suggested the subjects could not be differentiated from normosmics based on their BOLD signal from the primary olfactory area, orbitofrontal cortex, or the insular cortex.

Conclusion

There are large inter-individual variabilities for odor-induced brain activation among normosmic subjects and subjects with olfactory dysfunction, due to this variation, at present it appears problematic to diagnose olfactory dysfunction on an individual level using fMRI.

Mechanisms Linking Olfactory Impairment and Risk of Mortality

Olfaction is a sense involved in a complex set of tasks, influencing eating behavior, increasing awareness of environmental hazards and affecting social communication. Surprisingly, smell disorders are very frequent, especially in the elderly population. Several recent studies conducted mostly in older subjects have demonstrated a strong association between olfactory impairment and overall mortality risk, with anosmia being even more predictive of 5 years mortality risk than cardiovascular disease. Presently, the underlying pathophysiology linking olfactory impairment to mortality remains unknown and only putative mechanisms are suggested. This review aims to examine the link between olfactory impairment and mortality and to discuss existing ideas on underlying existing mechanisms including, (1) the effect of olfactory loss on nutrition, life-threatening situations and social interactions, (2) associated neurodegenerative diseases, (3) accelerated brain aging, and (4) reflection of general health status being reflected in olfactory function.

Olfactory bulb volume changes associated with trans-sphenoidal pituitary surgery

Objective

The trans-sphenoidal approach is most frequently used for pituitary adenoma (PA) enucleation. However, effects of this surgery on neighboring structures have received little attention so far. In particular, no investigations on olfactory bulb (OB) anatomy after trans-sphenoidal surgery have been reported. Because impairment of olfaction has been shown in small groups following trans-sphenoidal surgery we hypothesized that the transnasal approach is likely to alter OB volume which is associated with changes of olfactory function.

Methods

The study comprised 33 patients with pituitary adenoma (14 women and 19 men, mean age 50 years). Comprehensive assessment of olfactory function was conducted with the "Sniffin' Sticks" test kit. Based on magnetic resonance imaging scans OBs were measured before and approximately one year after trans-sphenoidal PA enucleation.

Results

Owing to postoperative non-compliance and MRI artifacts partly due to drill friction complete evaluation of “Sniffin' Sticks” in term of obtaining the TDI score was possible pre- and postoperatively in 21 patients whereas OB volumes were available in 32 patients. Approximately one year after surgery olfactory function was not significantly different from baseline. However, left- and right-sided OB volume in patients treated via trans-sphenoidal surgery decreased (p = 0.001). The side of the surgical approach did not affect OB volume in a side-specific manner. Changes in odor threshold were significantly correlated to changes in right-sided OB volume (r = 0.45, p = 0.024).

Conclusion

Overall olfactory performance one year after surgery was not significantly different from baseline. However, changes in OB volume are associated with changes in olfactory performance and OB volumes decreased in patients.

Chronic Exposure to High Altitude: Synaptic, Astroglial and Memory Changes

Long-term operations carried out at high altitude (HA) by military personnel, pilots, and astronauts may trigger health complications. In particular, chronic exposure to high altitude (CEHA) has been associated with deficits in cognitive function. In this study, we found that mice exposed to chronic HA (5000 m for 12 weeks) exhibited deficits in learning and memory associated with hippocampal function and were linked with changes in the expression of synaptic proteins across various regions of the brain. Specifically, we found decreased levels of synaptophysin (SYP) (p < 0.05) and spinophilin (SPH) (p < 0.05) in the olfactory cortex, post synaptic density−95 (PSD-95) (p < 0.05), growth associated protein 43 (GAP43) (p < 0.05), glial fibrillary acidic protein (GFAP) (p < 0.05) in the cerebellum, and SYP (p < 0.05) and PSD-95 (p < 0.05) in the brainstem. Ultrastructural analyses of synaptic density and morphology in the hippocampus did not reveal any differences in CEHA mice compared to SL mice. Our data are novel and suggest that CEHA exposure leads to cognitive impairment in conjunction with neuroanatomically-based molecular changes in synaptic protein levels and astroglial cell marker in a region specific manner. We hypothesize that these new findings are part of highly complex molecular and neuroplasticity mechanisms underlying neuroadaptation response that occurs in brains when chronically exposed to HA.

The therapeutic effect of deep brain stimulation on olfactory functions and clinical scores in Parkinson's disease

Deep brain stimulation (DBS) is still a highly effective treatment option that significantly improves motor function in advanced PD. Moreover, previous findings have shown that Olfactory dysfunction (OD) has been found in a majority of patients with Parkinson's Disease (PD). Despite this, the effect of DBS on the olfactory function is not fully understood. Here we aimed to determine the effect of STN DBS on OD by evaluating the olfactory functions in the preoperative and postoperative early stages (1st and 3rd months) in forty-five PD patients and 40 healthy controls. The therapeutic effect of DBS on the improvement of motor functions was parallelly investigated. We have observed that there was a significant improvement in OI in the 1st month and in all olfactory parameters (OT, ODI, OI, and TDI) in the 3rd month. In evaluating the motor functional scores, we have revealed a statistically significant (p < 0.001) difference between preoperative UPDRS-motor score (23 ± 7.3) and the postoperative 3rd month score (11.1 ± 5.1). Although Beck Depression and Anxiety scores were improved to a certain level in the 3rd month, this improvement was not at a statistically significant level (p > 0.05). As a conclusion, we have shown that STN-DBS improves the smell functions in PD within three months suggesting that the therapeutic effects of DBS might have a wide range of therapeutic spectrum. Despite some limitations (i.e., short follow-up period) our study gives a critical message that future studies are needed to evaluate the functional correlates of STN-DBS treatment in PD patients.

Olfactory and Gustatory Dysfunction in Patients With Autoimmune Encephalitis

Objective: To test the hypothesis that olfactory (OF) and gustatory function (GF) is disturbed in patients with autoimmune encephalitides (AE). Methods: The orthonasal OF was tested in 32 patients with AE and 32 age- and sex-matched healthy controls (HC) with the standardized Threshold Discrimination Identification (TDI) score. This validated olfactory testing method yields individual scores for olfactory threshold (T), odor discrimination (D), and identification (I), along with a composite TDI score. The GF was determined by the Taste Strip Test (TST). Results: Overall, 24/32 (75%) of patients with AE, but none of 32 HC (p < 0.001) had olfactory dysfunction in TDI testing. The results of the threshold, discrimination and identification subtests were significantly reduced in patients with AE compared to HC (all p < 0.001). Assessed by TST, 5/19 (26.3%) of patients with AE, but none of 19 HC presented a significant limitation in GF (p < 0.001). The TDI score was correlated with the subjective estimation of the olfactory capacity on a visual analog scale (VAS; r_s = 0.475, p = 0.008). Neither age, sex, modified Rankin Scale nor disease duration were associated with the composite TDI score. Conclusions: This is the first study investigating OF and GF in AE patients. According to unblinded assessment, patients with AE have a reduced olfactory and gustatory capacity compared to HC, suggesting that olfactory and gustatory dysfunction are hitherto unrecognized symptoms in AE. Further studies with larger number of AE patients would be of interest to verify our results.

Evidence for impaired olfactory function and structural brain integrity in a disorder of ciliary function, Usher syndrome

Diseases involving cilia dysfunction, such as Usher Syndrome (USH), often involve visual and auditory loss. Psychophysical evidence has suggested that this may also hold true for the peripheral olfactory domain. Here we aimed to go a step further by attempting to establish relations between the integrity of cortical structures and olfactory function in this condition. We investigated olfactory function for USH types 1 (USH1) and 2 (USH2). Bilateral olfactory bulb (OB) volume and olfactory sulcus (OS) depth were also analysed.

Thirty-three controls with no previous olfactory deficits were age, sex and handedness-matched to 32 USH patients (11 USH1, 21 USH2). A butanol detection threshold test was performed to measure olfactory function. For OB volume and OS depth, morphometric measurements were performed using magnetic resonance imaging (MRI) based on detailed segmentation by three independent operators. Averaged values across these were used for the statistical analyses. Total intracranial volume was estimated using Freesurfer to account for head size variability.

Olfactory threshold was significantly lower in controls when compared to USH, USH1, and USH2. OS depth was found to be shallower in both hemispheres in USH patients when compared with the control group. OB volume was not significantly different between control and USH groups, or respective subgroups. Nevertheless, butanol threshold was negatively correlated with the left OB volume for the USH type 1 subgroup. The main effect of OS depth reduction was found to be mainly due to the comparison between USH2 and controls.

Our results provide evidence for morphometric changes and olfactory dysfunction in patients with USH. This correlated with a reduction in left OB volume in the USH1 subgroup, the most severe USH phenotype. The main effect of reduced OS depth was found to stem mainly from USH2 raising questions regarding a possible complex interaction between sensory olfactory loss and central cortical changes in this disease.

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Evidence for olfactory loss in a disease involving ciliary dysfunction

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Olfactory sulcus depth is bilaterally reduced in Usher Syndrome (USH).

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Butanol threshold is negatively correlated with olfactory bulb volume in USH type 1.

Olfactory loss is associated with reduced hippocampal activation in response to emotional pictures

Emotional processing evolved within brain structures that were originally dedicated to olfactory function. Reduced olfactory function, absence of the olfactory bulb and the experimental removal of the olfactory bulb are associated with depressive behavior. Against this background, we hypothesized that olfactory dysfunction modifies the neural processing of non-olfactory emotion information. Using a functional magnetic resonance imaging design, we therefore tested whether people with and without impaired olfactory function differ in emotional perception and processing. Neural activity of 17 patients with acquired olfactory loss and 23 age- and sex-matched control participants were monitored in the MRI scanner, while they were presented with emotional and neutral pictures. Participants rated the valence and arousal for each picture after scanning. Patients showed reduced right hippocampal brain responses to emotional but not neutral pictures independent of their depressive symptoms. In addition, emotion-dependent activation in the hippocampus and insula was positively associated with the olfactory bulb (OB) volumes in healthy participants. Taken together, these findings suggest a disrupted neural processing of emotional pictures among patients with olfactory loss. This indicates a significant role of the neural olfactory trajectories for general emotion processing. Central emotion processing is reduced in olfactory disorders and relates to the OB volume in normosmic individuals.

Olfactory bulb atrophy in migraine patients

OBJECTIVE

Osmophobia and headache triggered by odors are commonly seen in migraine, and these are symptoms that differentiate migraine from other primary headaches. Since these odor-related symptoms are disease-specific, we aimed to measure the volume of olfactory bulb and depth of olfactory sulcus in migraine patients.

PATIENTS AND METHOD

A total of 93 subjects, consisting of 62 episodic migraine (32 with osmophobia, 30 without osmophobia) patients and 31 healthy controls, were included in this study. Diagnosis and classification of migraine were performed according to the beta version criteria of International Classification of Headache Disorders (ICHD-3 Beta version). Beck depression and beck anxiety inventory were applied to the patients, and the measurement of bilateral olfactory bulb volume (OBV) and olfactory sulcus depth (OSD) was performed manually in the brain magnetic resonance imaging (MRI).

RESULTS

More significantly in the left OBV, low OBV has been determined in migraine patients compared to the control group (p < 0.001, p = 0.020). When migraine patients with or without osmophobia were compared to the control group; OBV was determined to be the lowest in migraine group with osmophobia, and left-weighted bilateral OBV was determined to be low (p < 0.001, p = 0.046). No statistically significant difference was determined between groups in OSD measurements (p = 0.646, p = 0.490).

CONCLUSION

Left-weighted bilateral OBV atrophy determined in migraine patients may be guiding for the clarification of migraine pathophysiology and enlightening of the relation between migraine and odor.

Changes in olfactory bulb volume following lateralized olfactory training

Repeated exposure to odors modifies olfactory function. Consequently, "olfactory training" plays a significant role in hyposmia treatment. In addition, numerous studies show that the olfactory bulb (OB) volume changes in disorders associated with olfactory dysfunction. Aim of this study was to investigate whether and how olfactory bulb volume changes in relation to lateralized olfactory training in healthy people. Over a period of 4 months, 97 healthy participants (63 females and 34 males, mean age: 23.74 ± 4.16 years, age range: 19-43 years) performed olfactory training by exposing the same nostril twice a day to 4 odors (lemon, rose, eucalyptus and cloves) while closing the other nostril. Before and after olfactory training, magnetic resonance imaging (MRI) scans were performed to measure OB volume. Furthermore, participants underwent lateralized odor threshold and odor identification testing using the "Sniffin' Sticks" test battery.OB volume increased significantly after olfactory training (11.3 % and 13.1 % respectively) for both trained and untrained nostril. No significant effects of sex, duration and frequency of training or age of the subjects were seen. Interestingly, PEA odor thresholds worsened after training, while olfactory identification remained unchanged.These data show for the first time in humans that olfactory training may involve top-down process, which ultimately lead to a bilateral increase in olfactory bulb volume.

Improvement of Olfactory Function With High Frequency Non-invasive Auricular Electrostimulation in Healthy Humans

In past literature on animal models, invasive vagal nerve stimulation using high frequencies has shown to be effective at modulating the activity of the olfactory bulb (OB). Recent advances in invasive vagal nerve stimulation in humans, despite previous findings in animal models, used low frequency stimulation and found no effect on the olfactory functioning. The present article aimed to test potential effects of non-invasive, high and low frequency vagal nerve stimulation in humans, with supplementary exploration of the orbitofrontal cortex using near-infrared spectroscopy (NIRS). Healthy, male adult participants (n = 18) performed two olfactory tests [odor threshold test (OTT) and supra-threshold test (STT)] before and after receiving high-, low frequency vagal nerve stimulation and placebo (no stimulation). Participant's olfactory functioning was monitored using NIRS, and assessed with two behavioral olfactory tests. NIRS data of separate stimulation parameters were statistically analyzed using repeated-measures ANOVA across different stages. Data from olfactory tests were analyzed using paired parametric and non-parametric statistical tests. Only high frequency, non-invasive vagal nerve stimulation was able to positively modulate the performance of the healthy participants in the STT (p = 0.021, Wilcoxon sign-ranked test), with significant differences in NIRS (p = 0.014, post-hoc with Bonferroni correction) recordings of the right hemispheric, orbitofrontal cortex. The results from the current article implore further exploration of the neurocircuitry involved under vagal nerve stimulation and the effects of non-invasive, high frequency, vagal nerve stimulation toward olfactory dysfunction which showcase in Parkinson's and Alzheimer's Diseases. Despite the sufficient effect size (moderate effect, correlation coefficient (r): 0.39 for the STT) of the current study, future research should replicate the current findings with a larger cohort.

Comparative study of chemical neuroanatomy of the olfactory neuropil in mouse, honey bee, and human

Despite divergent evolutionary origins, the organization of olfactory systems is remarkably similar across phyla. In both insects and mammals, sensory input from receptor cells is initially processed in synaptically dense regions of neuropil called glomeruli, where neural activity is shaped by local inhibition and centrifugal neuromodulation prior to being sent to higher-order brain areas by projection neurons. Here we review both similarities and several key differences in the neuroanatomy of the olfactory system in honey bees, mice, and humans, using a combination of literature review and new primary data. We have focused on the chemical identity and the innervation patterns of neuromodulatory inputs in the primary olfactory system. Our findings show that serotonergic fibers are similarly distributed across glomeruli in all three species. Octopaminergic/tyraminergic fibers in the honey bee also have a similar distribution, and possibly a similar function, to noradrenergic fibers in the mammalian OBs. However, preliminary evidence suggests that human OB may be relatively less organized than its counterparts in honey bee and mouse.

Poor human olfaction is a 19th-century myth

It is commonly believed that humans have a poor sense of smell compared to other mammalian species. However, this idea derives not from empirical studies of human olfaction but from a famous 19th-century anatomist's hypothesis that the evolution of human free will required a reduction in the proportional size of the brain's olfactory bulb. The human olfactory bulb is actually quite large in absolute terms and contains a similar number of neurons to that of other mammals. Moreover, humans have excellent olfactory abilities. We can detect and discriminate an extraordinary range of odors, we are more sensitive than rodents and dogs for some odors, we are capable of tracking odor trails, and our behavioral and affective states are influenced by our sense of smell.

The olfactory bulb as the entry site for prion-like propagation in neurodegenerative diseases

Olfactory deficits are present in numerous neurodegenerative disorders and are accompanied by pathology in related brain regions. In several of these disorders, olfactory disturbances appear early and are considered as prodromal symptoms of the disease. In addition, pathological protein aggregates affect olfactory regions prior to other regions, suggesting that the olfactory system might be particularly vulnerable to neurodegenerative diseases. Exposed to the external environment, the olfactory epithelium and olfactory bulb allow pathogen and toxin penetration into the brain, a process that has been proposed to play a role in neurodegenerative diseases. Determining whether the olfactory bulb could be a starting point of pathology and of pathology spread is crucial to understanding how neurodegenerative diseases evolve. We argue that pathological changes following environmental insults contribute to the initiation of protein aggregation in the olfactory bulb, which then triggers the spread of the pathology within the brain by a templating mechanism in a prion-like manner. We review the evidence for the early involvement of olfactory structures in neurodegenerative diseases and the relationship between neuropathology and olfactory function. We discuss the vulnerability and putative underlying mechanisms by which pathology could be initiated in the olfactory bulb, from the entry of pathogens (promoted by increased permeability of the olfactory epithelium with aging or inflammation) to the sensitivity of the olfactory system to oxidative stress and inflammation. Finally, we review changes in protein expression and neural excitability triggered by pathogenic proteins that can promote pathogenesis in the olfactory bulb and beyond.

Expansion and Renormalization of Human Brain Structure During Skill Acquisition

Research on human brain changes during skill acquisition has revealed brain volume expansion in task-relevant areas. However, the large number of skills that humans acquire during ontogeny militates against plasticity as a perpetual process of volume growth. Building on animal models and available theories, we promote the expansion-renormalization model for plastic changes in humans. The model predicts an initial increase of gray matter structure, potentially reflecting growth of neural resources like neurons, synapses, and glial cells, which is followed by a selection process operating on this new tissue leading to a complete or partial return to baseline of the overall volume after selection has ended. The model sheds new light on available evidence and current debates and fosters the search for mechanistic explanations.

Recent advances in nanomedicine and survivin targeting in brain cancers

Brain cancer is a highly lethal disease, especially devastating toward both the elderly and children. This cancer has no therapeutics available to combat it, predominately due to the blood-brain barrier (BBB) preventing treatments from maintaining therapeutic levels within the brain. Recently, nanoparticle technology has entered the forefront of cancer therapy due to its ability to deliver therapeutic effects while potentially passing physiological barriers. Key nanoparticles for brain cancer treatment include glutathione targeted PEGylated liposomes, gold nanoparticles, superparamagnetic iron oxide nanoparticles and nanoparticle-albumin bound drugs, with these being discussed throughout this review. Recently, the survivin protein has gained attention as it is over-expressed in a majority of tumors. This review will briefly discuss the properties of survivin, while focusing on how both nanoparticles and survivin-targeting treatments hold potential as brain cancer therapies. This review may provide useful insight into new brain cancer treatment options, particularly survivin inhibition and nanomedicine.

Olfactory bulb volume predicts therapeutic outcome in major depression disorder

The volume of the olfactory bulb (OB) is strongly reduced in patients with major depressive disorder (MDD) and this group exhibits markedly decreased olfactory function. It has been suggested that olfactory input is important for maintaining balance in limbic neurocircuits. The aim of our study was to investigate whether reduced OB volume is associated with response to therapy in MDD. Twenty-four inpatients (all women, age 21-49 years, mean 38 ± 10 years SD) with MDD and 36 healthy controls (all women, age 20-52 years, mean 36 ± 10 years SD) underwent structural MRI. OB volume was compared between responders (N = 13) and non-responders (N = 11) to psychotherapy. Retest of OB volume was performed about 6 months after the end of therapy in nine of the patients. Therapy responders exhibited no significant difference in OB volume compared to healthy controls. However, average OB volume of non-responders was 23 % smaller compared to responders (p = .0011). Furthermore, OB volume was correlated with the change of depression severity (r = .46, p = .024). Volume of the OB did not change in the course of therapy. OB volume may be a biological vulnerability factor for the occurrence and/or maintenance of depression, at least in women.

Olfactory function in an excitotoxic model for secondary neuronal degeneration: Role of dopaminergic interneurons

Secondary neuronal degeneration (SND) occurring in Traumatic brain injury (TBI) consists in downstream destructive events affecting cells that were not or only marginally affected by the initial wound, further increasing the effects of the primary injury. Glutamate excitotoxicity is hypothesized to play an important role in SND. TBI is a common cause of olfactory dysfunction that may be spontaneous and partially recovered. The role of the glutamate excitotoxicity in the TBI-induced olfactory dysfunction is still unknown. We investigated the effects of excitotoxicity induced by bilateral N-Methyl-D-Aspartate (NMDA) OB administration in the olfactory function, OB volumes, and subventricular zone (SVZ) and OB neurogenesis in rats. NMDA OB administration induced a decrease in the number of correct choices in the olfactory discrimination tests one week after lesions (p<0.01), and a spontaneous recovery of the olfactory deficit two weeks after lesions (p<0.05). A lack of correlation between OB volumes and olfactory function was observed. An increase in SVZ neurogenesis (Ki67+ cells, PSANCAM+ cells (p<0.01) associated with an increase in OB glomerular dopaminergic immunostaining (p<0.05) were related to olfactory function recovery. The present results show that changes in OB volumes cannot explain the recovery of the olfactory function and suggest a relevant role for dopaminergic OB interneurons in the pathophysiology of recovery of loss of smell in TBI.

Anosmia-A Clinical Review

Anosmia and hyposmia, the inability or decreased ability to smell, is estimated to afflict 3-20% of the population. Risk of olfactory dysfunction increases with old age and may also result from chronic sinonasal diseases, severe head trauma, and upper respiratory infections, or neurodegenerative diseases. These disorders impair the ability to sense warning odors in foods and the environment, as well as hinder the quality of life related to social interactions, eating, and feelings of well-being. This article reports and extends on a clinical update commencing at the 2016 Association for Chemoreception Sciences annual meeting. Included were reports from: a patient perspective on losing the sense of smell with information on Fifth Sense, a nonprofit advocacy organization for patients with olfactory disorders; an otolaryngologist's review of clinical evaluation, diagnosis, and management/treatment of anosmia; and researchers' review of recent advances in potential anosmia treatments from fundamental science, in animal, cellular, or genetic models. As limited evidence-based treatments exist for anosmia, dissemination of information on anosmia-related health risks is needed. This could include feasible and useful screening measures for olfactory dysfunction, appropriate clinical evaluation, and patient counseling to avoid harm as well as manage health and quality of life with anosmia.

Olfactory Loss and Regain: Lessons for Neuroplasticity

For the visual and auditory senses, an array of studies has reported on neuronal reorganization processes after sensory loss. In contrast to this, neuroplasticity has been investigated only scarcely after loss of the olfactory sense. The present review focuses on the current extent of literature on structural and functional neuroplasticity effects after loss, with a focus on magnetic resonance imaging-based studies. We also include findings on the regain of the olfactory sense, for example after successful olfactory training. Existing studies indicate that widespread structural changes beyond the level of the olfactory bulb occur in the brain after loss of the olfactory sense. Moreover, on a functional level, loss of olfactory input not only entails changes in olfaction-related brain regions but also in the trigeminal system. Existing evidence should be strengthened by future longitudinal studies, a more thorough investigation of the neuronal consequences of congenital anosmia, and the application of state-of-the-art neuroimaging methods, such as connectivity analyses and joint analyses of brain structure and function.