Investigating the brain functional connectivity changes in subjects with post-traumatic olfactory disorder before and after low-power laser irradiation using fMRI

Background and Aim : Smell disorders have a strong effect on different aspects of life and must be taken seriously. Following head trauma in patients with post-traumatic olfactory disorder, the cribriform plate of ethmoid bone may undergo fibrotic healing, resulting in smell senses disability. Low-level laser therapy (LLLT) can be a therapeutic method in order to remove the fibrosis tissue and recover the smell function. In this study we investigated patients with post-traumatic olfactory disorder before and after low-level laser irradiation using fMRI. The results showed differences between pre and post LLLT in olfactory-related regions functional network.Methods : 16 patients with post-traumatic olfactory disorder confirmed with Sniffin Sticks test, were divided into three groups; a control group with 8 subjects and two experimantal groups with 4 subjects each. Laser irradiation with different durations, 10 and 20 minutes, 8 sessions each, were conducted to the experimental groups. All subjects underwent two fMRI sessions with time interval of 75 days. The time interval was chosen according to the treatment periods of two experimental groups. The fMRI task was a block design containing two odors, Vanillin and Rose, which were presented by the help of an home-made olfactometer. Analysis of functional images was done using FSL software and CONN toolbox.Results : Activation was found significantly in laser II group after LLLT in the right fusiform and corpus callosom, as well as sub-gyral, right parahippocampus, medial frontal, middle temporal gyrus and right cerebellum in response to Vanillin and Rose, repectively. Activation was also found in control subjects in the postcentral and anterior cingulate gyrus, after the time period. There was no significant activation in laser I group after treatment. Positive correlation was seen between IFG and thalamus toward piriform cortex in both laser groups. After LLLT, both groups manifested great modifications in functional connections between olfactory areas. IFG, orbitofrontal and parahippocampal cortex were mainly involved in functional connectivity network compared with pre-scan images.Conclusion : Our results support the hypothesis that low-level laser might have a positive effect on axon regeneration in olfactory epithelium and create new connections between olfactory nerves, in terms of changes in functional connectivity. Specially, at higher irradiation times, more promissing effects could be observed.

کلیدواژه ها:

Olfactory disorder ، Trauma ، Low-level laser ، Functional connectivity ، fMRI