Functional MRI in assessing brain cortex activation patterns in response to olfactory stimuli

Objective: quantitative assessment of the activation areas of the cerebral cortex in women and men in response to olfactory stimuli using functional magnetic resonance imaging (fMRI).

Material and methods. The study included 14 non-smoking volunteers who were right-handed from birth (8 women and 6 men; mean age – 32.7±6.4 years), without anamnestic and clinical signs of diseases of the nervous system, nasopharynx and oropharynx, and without anosmia during the COVID-19 period. fMRI was performed on a Signa PET/MR 3.0 T scanner (GE Healthcare) with a 32-channel coil. Each olfactory stimulus (lavender and pine needles) was delivered alternately from a 200 ml syringe containing cotton wool soaked in essential oil through a PERFOMA-Judkins catheter. The syringe was opened for 4 seconds for delivery, after which delivery was stopped and the catheter was aspirated to remove the residual odour. Odours were presented at 40 seconds intervals and each odour was presented 4 times. Data analysis focused on the primary olfactory cortex (POC), orbitofrontal olfactory cortex (OOC), insular cortex (IC), and motor cortex (Brodmann’s areas 4 and 6).

Results. All subjects showed activation of the POC, OOC, IC and areas 4 and 6 for both odour stimuli, with a slight dominance of the right hemisphere. Lavender odour often led to a stronger activation of the olfactory and motor cortex than pine needle odour. The individual activation map of areas 4 and 6 elicited by lavender odour was characterized by greater variability than the map for pine needle odour. The intensity of activation in response to both odours was higher in women than in men.

Conclusion. The odours of lavender and pine needles activate not only the olfactory areas of the cortex but also areas 4 and 6 and are characterized by certain interhemispheric and gender differences.

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