Concussion | My Safe Pass

Can a concussion cause loss of smell?

It's long been known that people who suffer a major concussion can lose their sense of smell temporarily and also develop affective problems, such as anxiety and depression. Now scientists have found that's true even for people who get a minor concussion. Jul 23, 2019

Hit your head, lose your sense of smell - ScienceDaily

"Surprisingly, a test of olfactory function is not currently a part of the concussion protocol even though smell loss has been a common occurrence following head injuries. A test of olfactory function and CTE in real time would be a “game-changer” in our understanding of repetitive head injuries. A 5-min smell test given by a single technician could objectively track CTE over time." Science Direct.com

NIH - Head trauma and olfactory function
Click Here for links to 62 studies. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6051255/

Disorders of Taste and Smell in clinical neurology. These disorders commonly occur in head trauma. Click here https://pubmed.ncbi.nlm.nih.gov/28375912/

Abstract

Chemosensory disorders, primarily olfactory, have diagnostic significance for prevalent human illnesses, but the multitude of smells makes measuring function appear daunting. The olfactory system operates under dynamic natural sensing conditions in which many individual odor chemicals are waxing and waning. Yet, in experimentally controlled simulations, mixture-component selective adaptation shows individual or shared prominent characteristic odors are detected but molecular stimulus features are not. As in other biological chemical signaling systems, including taste, odors activate dedicated receptors (OR). Given rapid OR adaptation with the passage of time, individual odor recognition is momentary. Receptive dendrites of the nearly 400 genetically variable human-OR in the olfactory epithelium critically project axons to the olfactory bulb through perforations in the cribriform plate of the skull. Analytic chemical-quality codes detect single odor-mixture components. However, identities of no more than 3 or 4 most salient odors are perceived due to central mixture-suppression, the mutual inhibition among diverse olfactory-bulb or cortical neurons. The componental codes allow olfaction to readily discern odor quality and valence of a wide range of unrelated chemicals, a few at a time. Head trauma may result in a partial or complete loss of smell and facial trauma a loss of taste-nerve function. Testing smell could plot the course of recovery from chronic traumatic encephalopathies that prevail in contact sports. Measuring brain function with olfaction would provide simpler and more direct monitoring of prognosis than biochemical sensors.

Keywords

Mixture-component perception

Head trauma

Contact sports

Introduction

Chemosensory disorders have diagnostic significance for prevalent human illnesses. Primarily olfactory, they are frequently considered gustatory due to the oral retro-nasal origin of some odorous volatiles.1 However, the multitude of possible smells, recently exaggerated from thousands to more than a trillion,2 makes measuring individual odor sensing appear daunting.3, 4 Furthermore, this conundrum has led to attempts to segregate roles of relevant functional groups,5 or use of crowd-sourcing methods,6 to count the number of recognizable multi-component odor objects that an individual can recognize.7

Odor component recognition

As in other biological chemical signaling systems, including taste-sensing8, 9, 10; distinct odors likely activate dedicated receptors (OR).11, 12 However, given the rapid odor adaptation with the passage of time, odor recognition is momentary.4 The ortho-nasal odor-stimulus is limited to the inhalation phase by the act of sniffing,13 and on the same time scale as sniffing, the odor rapidly adapts. To further complicate the stimulus situation, odor sensing occurs in dynamic natural sensing settings in which odors of many individual odor chemicals are simultaneously either waxing or waning. The olfactory system needs to be able to identify chemicals of harm or value under these conditions. Surprisingly, this may be accomplished by a combination of ‘mixture suppression and selective adaptation.’

In experimentally controlled simulations, mixture-component selective adaptation shows individual or shared prominent characteristic odors (‘odor notes’) are detected by humans.4 However, individual molecular stimulus features are not. The perceptual saliencies of two individually presented components, A and B ‘odor notes’, are represented by bright colors in Fig. 1. The saliencies are reduced when both components are within a mixture (below), the feature known as ‘mixture suppression’ in olfaction,14, 15, 16 and taste.17 However, when component A alone is adapted for 10 s (center), its ambient salience in the following mixture (below) is further weakened but un-adapted component B is ‘released’ from mixture inhibition. This startling outcome resulting by combining ‘mixture suppression’ and ‘selective adaptation’ of independent stimuli (defined as those that do not cross-adapt) explains how the olfactory system is able to identify individual mixture components in few-component mixtures.3, 18, 4 Thus, the odor mixtures are analyzed; they are not synthesized by a combinatorial process into a distinctly different quality. Gustatory mixtures of independent taste stimuli are also analyzed via the combination of ‘mixture suppression’ and ‘selective adaptation’.19

Conclusions

Simpler and more direct measurement of living brain function may be achieved with olfactory testing during football games and in other sports where players experience ‘repetitive head impacts”. To date, the U.S. National Football League concussion protocol involves observation and evaluations of cognitive function from onset to recovery. Surprisingly, a test of olfactory function is not currently a part of the concussion protocol even though smell loss has been a common occurrence following head injuries. A test of olfactory function and CTE in real time would be a “game-changer” in our understanding of repetitive head injuries. A 5-min smell test given by a single technician could objectively track CTE over time.

Conflict of interest/Financial disclosures

This work was supported by the University of Connecticut Foundation, the School of Dental Medicine and the University of Connecticut Clinical Research Center.

References

R.L. Doty

Olfactory dysfunction and its measurement in the clinic

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ArticleDownload PDFCrossRefView Record in ScopusGoogle Scholar

C. Bushdid, M.O. Magnasco, L.B. Vosshall, A. Keller

Humans can discriminate more than 1 trillion olfactory stimuli

Science, 343 (2014), pp. 1370-1372