Non-invasive Brain Stimulation with a Monophasic TMS Pulse: A Pilot Study of BDNF (rs6265) and COMT (rs4680) Gene Polymorphisms
Our goal was to evaluate genetic and gender differences in motor threshold (MT) using monophasic single pulse Transcranial Magnetic Stimulation (TMS).
Methods. In this pilot study, we used TMS over dominant primary motor cortex and recorded motor evoked potentials (MEP) from the contralateral which yielded a higher MT than other TMS methods. We applied the monophasic stimulation to evaluate phenomena of intracortical excitation and inhibition of neuromuscular activity within the upper limb muscles. 112 volunteers (age: mean/max/min 23/41/18 years; 63 females).
Results. The presence of a relatively high MT value (92-100% of the amplitude on the TMS stimulator, or not any MEP) that was revealed for 61 participants (54.4%); this is essential for future planning of experimentаl and clinical investigations. We have not found a significant relationship between BDNF (rs6265) and COMT (rs4680) gene polymorphisms and MT value (Kruskal-Wallis test, 6 subgroups polymorphism p=0.696). Also, we did not find a significant difference in the value of MT in men and women (Mann-Whitney test, p=0.279).
On the next step we have decided to apply statistical analysis of MT, candidate genes and non-brain structures based on the sMRI scans. This will allow an assessment of the contribution of extra-axial structures to the somatotopy of the processes of excitation and inhibition of the motor cortex of the brain, along with an assessment of (a) their relationship with the individual amplitude (MT) to select the optimal level of stimulation; and (b) the contribution of the genetic factor.
Conclusion. We did not find significant relationships between BDNF and СOMT polymorphisms, as well as gender and MT level. We plan further tasks to evaluate the effect of extra-axial structures on MT levels.