Impact of uncertain transcranial magnetic stimulation coil position and orientation in the stimulation for a motor cortex

Transcranial magnetic stimulation (TMS) is a non-invasive brain stimulation technique to modify neural excitability. The effectiveness of TMS experiments critically depends on precise TMS coil position and orientation. There are many TMS coil positioning methods have been used to optimal TMS efficiency. But, sometimes these data are not always precise, and it will make the results uncertainty. To quantify the uncertainty of induced electric field (E-field) in human brain, multi-variate generalized polynomial chaos expansions of the model solutions are used based on uncertain TMS coil position and orientation. Sensitivity of the quantities of interest is investigated for the induced E-field. The results demonstrate that the position of TMS coil has much more effect on induced E-field in human brain than the effect by the orientation of TMS coil. But the effect of TMS coil rotation on Z axis cannot be neglected.