Change in Functional Brain Activation Patterns Induced by Olfactory Stimulation in Multiple Sclerosis

Background: Olfactory disorder is one of the commonly appearing symptoms in diseases like Parkinson's disease (PD) and Alzheimer's disease (AD). However, reports of olfactory changes in multiple sclerosis (MS) are scarce and usually ignored or seldom recognized by clinicians. The majority of current research is based on subjective answers obtained by smelling odorants. Objective: To gain better insights into the central brain regions involved in the olfactory process. We measured preliminary contrast assessment characteristics of brain activation in MS patients and healthy controls using functional magnetic resonance imaging (fMRI) under an odor stimulation task. Methods: Olfactory event-related fMRI was used to assess the olfactory network neuronal activity during passively inhaled volatile gases of lavender and rose solutions alternately in 18 MS patients and 20 healthy sex- and age-matched adults. Spearman correlation analysis was conducted between the lesions in central and olfactory-induced activated brain regions. Results: We observed significant reductions in the number of activated brain areas compared with healthy controls in MS patients under a standard activation mode; the right insula, right amygdala, right inferior frontal gyms, right frontal middle gyms, and left supramarginal gyrus were activated in MS patients (t = 2.04, P < 0.05). Meanwhile, the intensity of the activated olfactory brain network revealed attenuation. The Spearman correlation analysis indicated the distribution and number of demyelination lesions, exerting a little impact on major activation of brain regions during olfactory stimulation (r = -0.524, P = 0.054). Conclusion: This study establishes that olfaction-related brain regions were altered in patients with MS confirmed by fMRI. The finding refreshes the awareness that olfactory disturbance involved just in structural pathology like olfactory bulbs and tracts or olfactory sulcus, which reportedly is responsible for the deficits.