FMRI correlates of olfactory processing in typically-developing school-aged children

Abstract

Human olfactory processing is understudied relative to other sensory modalities, despite its links to neurodevelopmental and neurodegenerative disorders. To address this limitation, we developed a fast, robust fMRI odor paradigm that is appropriate for all ages and levels of cognitive functioning. To test this approach, thirty-four typically developing children aged 7-12 underwent fMRI during brief, repeated exposure to phenylethyl alcohol, a flower-scented odor. Prior to fMRI scanning, olfactory testing (odor detection and identification) was conducted. During fMRI stimulus presentation, odorant release was synchronized to each participant's inspiratory phase to ensure participants were inhaling during the odorant exposure. Between group differences and correlations between activation and odor detection threshold scores were tested using the FMRIB Software Library. Results demonstrated that our 2-minute paradigm significantly activated primary and secondary olfactory regions. In addition, a significant relationship between odor detection threshold and higher activation in the right amygdala and lower activation in the left frontal, insular, occipital, and cerebellar regions was observed, suggesting that this approach is sensitive to individual differences in olfactory processing. These findings demonstrate the feasibility of studying olfactory function in children using brain imaging techniques.

Short or long runs: An exploratory study of odor‐induced fMRI design

“…For example, a fast repetition time (TR < 1 second) combined with a short stimulation length (6‐second odor stimulation in a 20‐second block) was associated with more rapid increase of BOLD signal in the olfactory regions . A short total odor exposure time may prevent rapid adaptation in the primary olfactory areas . Nevertheless, these studies, including the current one, are based on group inference.…”

“…Obviously this happened despite the pulsed delivery of odors in the current study. It has been argued that in addition to a short task duration, the stimulation within runs (eg, in each block) is also important for a consistent activation across the primary (piriform) and secondary olfactory areas . For example, a fast repetition time (TR < 1 second) combined with a short stimulation length (6‐second odor stimulation in a 20‐second block) was associated with more rapid increase of BOLD signal in the olfactory regions .…”

Individual variability of olfactory fMRI in normosmia and olfactory dysfunction

“…Besides, physiological factors such as respiration and metabolic status also influence the sensitivity for detecting differences between groups. Some approaches have been suggested to increase SNR regarding the odor stimulation paradigm, e.g., short odor stimulation time [ 23 , 24 ] rapid repetition time (< 1 s) during brain image acquisition [ 25 ] or task protocols applied (e.g. synchronization of the breathing cycle with odor stimulation) [ 23 ] In addition, sequential stimulation with increasing intensities of odor may potentially offset potential habituation effects [ 26 ] Moreover, the presently used odors were familiar food-related.…”

“…One recent study demonstrated that odor-induced brain activation in the amygdala covaried with the participants’ odor sensitivity [ 23 ]. However, such correlation does not ensure the generalizability of the established relationship to out-of-sample individual subjects.…”

FMRI activation to cannabis odor cues is altered in individuals at risk for a cannabis use disorder

“…The olfactometer used in this experiment was built in the Instrument Development Laboratory at the University of Washington Center on Human Development (see Kleinhans et al., 2018, for more detail). The olfactometer design was based on Lorig, Elmes, Zald, and Pardo (1999), with a modification of the odorant cylinders/manifold and nosepiece.…”