Olfactory sniffing signals consciousness in unresponsive patients with brain injuries

Arzi, Anat; Rozenkrantz, Liron; Gorodisky, Lior; Rozenkrantz, Danit; Holtzman, Yael; Ravia, Aharon; Bekinschtein, Tristán A.; Galperin, Tatyana; Krimchansky, Ben-Zion; Cohen, Gal; Oksamitni, Anna; Aidinoff, Elena; Sacher, Yaron; Sobel, Noam

doi:10.1038/s41586-020-2245-5

Cited by 41 publications

(30 citation statements)

References 51 publications

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“…We used a recently published method for nasal airflow analysis ( Arzi et al 2020 ). This method allowed comparing of respiration across a session and between sessions, and used low-pass filters and adaptive hysteresis to automatically identify inhales and exhales.…”

Section: Methodsmentioning

confidence: 99%

Odor Canopy: A Method for Comfortable Odorant Delivery in MRI

et al. 2021

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Functional magnetic resonance imaging (fMRI) has become the leading method for measuring the human brain response to sensory stimuli. However, olfaction fMRI lags behind vision and audition fMRI for two primary reasons: First, the olfactory brain areas are particularly susceptible to imaging artefacts, and second, the olfactory stimulus is particularly difficult to control in the fMRI environment. A component of the latter is related to the odorant-delivery human-machine interface, namely the point where odorants exit the dispensing apparatus to reach at the nose. Previous approaches relied on either nasal cannulas or nasal masks, each associated with particular drawbacks and discomforts. Here we provide detailed descriptions and instructions for transforming the MRI head-coil into an olfactory microenvironment, or odor canopy, where odorants can be switched on and off in less than 150 milliseconds without cannula or mask. In a proof-of-concept experiment we demonstrate that odor canopy provides for clearly dissociable odorant presence and absence, with no non-olfactory cues. Moreover, we find that odor canopy is rated more comfortable than nasal-mask, and we demonstrate that using odor canopy in the fMRI generates a typical olfactory brain-response. We conclude in recommending this approach for minimized discomfort in fMRI of olfaction.

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Section: Methodsmentioning

confidence: 99%

Odor Canopy: A Method for Comfortable Odorant Delivery in MRI

et al. 2021

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“…In addition, pathological tau and amyloid protein accumulations have been demonstrated in the olfactory epithelium/mucosa (OE) (Lee et al, 1993) and olfactory end-terminals including the entorhinal cortex (EC) in AD patients (Näslund et al, 2000;Desikan et al, 2012;Khan et al, 2014). In a recent research, it has also been shown that 100% (specificity) of patients who respond to olfactory stimulus in the unresponsive states (or low level of consciousness) regained consciousness (Arzi et al, 2020).…”

Section: Introductionmentioning

confidence: 99%

Optimized Electrode Placements for Non-invasive Electrical Stimulation of the Olfactory Bulb and Olfactory Mucosa

et al. 2020

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The olfactory system is known to be dysfunctional in the early stages of Parkinson’s disease (PD) and Alzheimer’s disease (AD). It is also shown that intact olfactory function can be a key role player for regaining consciousness after brain injuries. Modulation of the olfactory regions has been attempted successfully with electrical stimulation over the years, either directly (transethmoidally, intraoperatively, internasally, etc.) or indirectly through the vagus nerve. We sought to develop a means of delivering optimized electrical stimulation to the olfactory region in a non-invasive fashion and in a way that is simpler, easier, and less cumbersome. The ultimate goal was to develop a system that would allow easier testing in future clinical trials presenting an opportunity to fully develop this potential treatment option. We devised six potential electrode placements leveraging commonly accepted facts of electrical stimulation, easier access through relatively higher conductive pathways into the brain, and practicality. Using an ultra-high-resolution finite element model, we screened each one of these montages for their ability to target the olfactory regions primarily and thereafter for select sub-cortical regions implicated in the pathogenesis of PD and AD. Modeling results indicate that some placements do result in inducing meaningful electric field magnitudes in the regions of interest. A practical headgear concept is proposed to realize the most ideal configuration. Our results pave the way for developing the first non-invasive electrical stimulation wearable system for targeting the olfactory regions which can help to alleviate the symptoms or suppress the progression of these neurological disorders.

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“…We typically define a sniff as a greater than 15% change in normalized sniff volume from baseline respiration (increase (as often after pleasant odours) or decrease (as often after unpleasant odours)), and/or a modulation in sniff volume reflecting a shift in standard deviation (s.d.) > 0.35 over ongoing respiration [14]. We found that nasal airflow more than doubled when the hand was at the nose (12 of 17 participants increased (binomial probability p = 0.047), group baseline flow = 112.75 ± 75.56 ml s −1 , hand-at-face flow = 237.81 ± 220.82 ml s −1 , t 16 = 2.37, p = 0.03) [12], or in other words, people are sniffing their own hands (figure 1b).…”

Section: Is Face-touching An Olfactory Behaviour?mentioning

confidence: 99%

Are humans constantly but subconsciously smelling themselves?

Perl

Mishor

Ravia

et al. 2020

Phil. Trans. R. Soc. B

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All primates, including humans, engage in self-face-touching at very high frequency. The functional purpose or antecedents of this behaviour remain unclear. In this hybrid review , we put forth the hypothesis that self-face-touching subserves self-smelling. We first review data implying that humans touch their faces at very high frequency. We then detail evidence from the one study that implicated an olfactory origin for this behaviour: This evidence consists of significantly increased nasal inhalation concurrent with self-face-touching, and predictable increases or decreases in self-face-touching as a function of subliminal odourant tainting. Although we speculate that self-smelling through self-face-touching is largely an unconscious act, we note that in addition, humans also consciously smell themselves at high frequency. To verify this added statement, we administered an online self-report questionnaire. Upon being asked, approximately 94% of approximately 400 respondents acknowledged engaging in smelling themselves. Paradoxically, we observe that although this very prevalent behaviour of self-smelling is of concern to individuals, especially to parents of children overtly exhibiting self-smelling, the behaviour has nearly no traction in the medical or psychological literature. We suggest psychological and cultural explanations for this paradox, and end in suggesting that human self-smelling become a formal topic of investigation in the study of human social olfaction. This article is part of the Theo Murphy meeting issue ‘Olfactory communication in humans’.

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Olfactory sniffing signals consciousness in unresponsive patients with brain injuries

Cited by 41 publications

References 51 publications

Odor Canopy: A Method for Comfortable Odorant Delivery in MRI

Odor Canopy: A Method for Comfortable Odorant Delivery in MRI

Optimized Electrode Placements for Non-invasive Electrical Stimulation of the Olfactory Bulb and Olfactory Mucosa

Are humans constantly but subconsciously smelling themselves?

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