Odor Canopy: A Method for Comfortable Odorant Delivery in MRI

Abstract

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.

A novel odor stimulation system in freely moving, behaving animals

“…2c). These data are comparable to the olfactory stimulation systems described in other studies (Bestgen & Schulze 2016; Lior & Ethan 2021). To summarize, our odor stimulation system is relatively naturalistic and allows for close to square‐wave administration of odors.…”

Sniffing the human body volatile hexadecanal blocks aggression in men but triggers aggression in women

“…This was done to minimize transferring of emotions, strategies, etc., between odor conditions. Odorant delivery in the MRI Odorants were delivered using a computer-controlled air-dilution olfactometer that was optimized for naturalistic delivery in the MRI (71). The olfactometer emitted a constant flow of olfactometer air (1.5 l/min) that carried embedded 10-s pulses of odorant (HEX or control).…”

fNIRS a novel neuroimaging tool to investigate olfaction, olfactory imagery, and crossmodal interactions: a systematic review

“…A prominent research theme across the reviewed articles was the study of hedonics; ten studies considered the impact of odour valence on olfactory processing. Seven of these articles directly contrasted odour valence: two behavioural ( Hudry et al, 2014 ; Kärnekull et al, 2021 ) and five neuroimaging ( Royet et al, 2003 ; Bensafi et al, 2007 ; Callara et al, 2021 ; Gorodisky et al, 2021 ; Torske et al, 2022 ). A further three papers involved discussion of the impact of odour hedonicity on olfactory processes, but did not directly manipulate odour pleasantness ( Bensafi and Rouby, 2007 ; Plailly et al, 2007 ; Morrot et al, 2012 ).…”

“…Poor motion tolerance can limit participants’ ability to interact with olfactory stimuli in a naturalistic manner. Methods of odour delivery must also be carefully designed to ensure instrumentation does not introduce noise or artefacts in neuroimaging data ( Gorodisky et al, 2021 ). Neuroimaging environments, particularly the MRI scanner environment, have been demonstrated to impede perceptual decision-making and attentional focus ( Van Maanen et al, 2015 ).…”

“…Poor motion tolerance can limit participants' ability to interact with olfactory stimuli in a naturalistic manner. Methods of odour delivery must also be carefully designed to ensure instrumentation does not introduce noise or artefacts in neuroimaging data (Gorodisky et al, 2021).…”