Investigation of the Changes of the Brain Effective Connectivity Network through Olfactory Training and Rehabilitation in the patient with Hyposmia Disorder, using Functional Magnetic Resonance Imaging (fMRI)

Abstract

Introduction: we investigated if and how the olfactory training (OT) scheme has effects on resting-state effective connectivity among piriform cortex, amygdala (AMY), orbitofrontal cortex (OFC), insula, and cingulate cortex, which are among the most possible areas participating in olfactory related processes. Objective: Investigation of the brain effective connectivity changes through olfactory training in post-traumatic patients with smell disorders using fMRI Methods and materials: 28 posttraumatic patients with olfactory dysfunctions participated in this study. The olfactory performance of the subjects was evaluated using the Sniffin’ Sticks test kit. Patients randomly were put in three groups, namely control, conventional, and modified olfactory training. After the first fMRI examination, the subjects, who were in conventional and modified OT groups, were trained for 16 weeks and the control group did not receive any treatment. At last, participants of all groups underwent the smell testing and the MRI examination again, similar to those prior to the OT. Wilcoxon signed-rank test was used to compare the olfactory performance of each group before and after the OT scheme, and ANCOVA for comparison of three groups before and after the training scheme was adopted. Spectral dynamic causal modeling was applied to resting-state fMRI to identify alterations in effective connectivity due to the smell training. Results: our results revealed that the overall olfactory performance of the groups that implemented training schemes and odor discrimination score of the conventional olfactory training group got significantly better. However, odor discrimination, identification, and threshold scores of modified olfactory training group did not change meaningfully. Compared to the control group, patients in the conventional group had increased self-inhibitory connection of OFC and excitatory connectivity from the cingulate cortex to insula. Moreover, the excitatory connectivity from OFC to the cingulate cortex weakens after performing the conventional olfactory training scheme. Conclusion: this study shows that the smell training scheme can cause changes in resting-state effective connectivity parameters that can be attributed to the improvement of the odor discrimination task.