[How we smell and what it means to us: basic principles of the sense of smell]

Olfactory Dysfunction in Adults from Rio Grande do Norte: A Cross-Sectional Study

Introduction  Smell is one of the senses of the human body, and it can be affected by several factors, such as viral infections, traumatic brain injury, iatrogenesis, smoking, and neurodegenerative and systemic diseases. Objectives  The main goal of the present study is to describe the epidemiology of olfactory disorders in Rio Grande do Norte (RN). More specifically, to determine the prevalence of olfactory dysfunction and to identify the main risk factors related to these dysfunctions in the state's population. Methods  A total of 180 volunteers living in the RN underwent the Connecticut Clinical Research Center (CCCRC) smell test and a clinical and demographic questionnaire. Results  A total of 58.89% of the patients presented normosmia and 87.78% were classified as having between normal and mild hyposmia. A statistically significant relationship was found between worse performance in the test and nasal surgery ( p  = 0.041) and the subjective feeling of not having an accurate sense of smell ( p  = 0.006 on the right nostril). There was no statistical relationship between the olfactory status and the report of coronavirus disease 2019 (COVID-19) infection ( p  = 0.254). Conclusion  The occurrence of altered sense of smell in our study was different from that reported in other studies that used the same test. The relationship with COVID-19 was not clear.

Sensory Dysfunction in Old Age

BACKGROUND

The senses serve as the crucial interface between the individual and the environment. They are subject to aging and disease processes.

METHODS

This review is based on pertinent publications retrieved by a selective search in the Medline and Cochrane Library databases.

RESULTS

Approximately 40% of persons aged 70 to 79 manifest dysfunction in at least one, and more than 25% in multiple senses. Sensory changes are accompanied by diverse comorbidities which depend on the particular sense(s) affected. The presence of sensory deficits is associated with an increased risk of developing dementia (OR: 1.49 [95% confidence interval: 1.12; 1.98] for dysfunction in a single sensory modality, 2.85 [1.88; 4.30] for dysfunction in three or more sensory modalities). The risk of developing depressive symptoms is elevated as well (OR 3.36 [2.28; 4.96]). The individual's ability to cope with the demands of everyday life is largely determined by the ability to carry out multisensory integration, in which the perceptions of the different senses are bound together. This function itself is subject to age-related changes that can be either adaptive or maladaptive; it can, therefore, serve as an indicator for pathological aging processes.

CONCLUSION

Sensory dysfunction in old age should be detected as early as possible. This implies the need for close collaboration of all of the involved disciplines. It would be desirable to develop sensory screening tests as well as a procedure for testing multisensory integration in routine clinical practice.

Principles of odor coding in vertebrates and artificial chemosensory systems

The biological olfactory system is the sensory system responsible for the detection of the chemical composition of the environment. Several attempts to mimic biological olfactory systems have led to various artificial olfactory systems using different technical approaches. Here we provide a parallel description of biological olfactory systems and their technical counterparts. We start with a presentation of the input to the systems, the stimuli, and treat the interface between the external world and the environment where receptor neurons or artificial chemosensors reside. We then delineate the functions of receptor neurons and chemosensors as well as their overall I-O relationships. Up to this point, our account of the systems goes along similar lines. The next processing steps differ considerably: while in biology the processing step following the receptor neurons is the "integration" and "processing" of receptor neuron outputs in the olfactory bulb, this step has various realizations in electronic noses. For a long period of time, the signal processing stages beyond the olfactory bulb, i.e., the higher olfactory centers were little studied. Only recently there has been a marked growth of studies tackling the information processing in these centers. In electronic noses, a third stage of processing has virtually never been considered. In this review, we provide an up-to-date overview of the current knowledge of both fields and, for the first time, attempt to tie them together. We hope it will be a breeding ground for better information, communication, and data exchange between very related but so far little connected fields.

The Olfactory System Revealed: Non-Invasive Mapping by using Constrained Spherical Deconvolution Tractography in Healthy Humans

Although the olfactory sense has always been considered with less interest than the visual, auditive or somatic senses, it does plays a major role in our ordinary life, with important implication in dangerous situations or in social and emotional behaviors. Traditional Diffusion Tensor signal model and related tractography have been used in the past years to reconstruct the cranial nerves, including the olfactory nerve (ON). However, no supplementary information with regard to the pathways of the olfactory network have been provided. Here, by using the more advanced Constrained Spherical Deconvolution (CSD) diffusion model, we show for the first time in vivo and non-invasively that, in healthy humans, the olfactory system has a widely distributed anatomical network to several cortical regions as well as to many subcortical structures. Although the present study focuses on an healthy sample size, a similar approach could be applied in the near future to gain important insights with regard to the early involvement of olfaction in several neurodegenerative disorders.