Inter-individual variation in the efficient stimulation site for magnetic brainstem stimulation

ObjectiveTo investigate inter-individual variation in the efficiency of magnetic brainstem stimulation (BST) with regard to the stimulation site.MethodsWe studied 31 healthy subjects, using a right hand muscle as a recording site. Three stimulation sites were compared: BST over the inion (inion BST), and BST over the midpoint between the inion and the right (ipsilateral BST) or left (contralateral BST) mastoid process. Five suprathreshold BSTs were performed for each stimulation site using the same stimulation intensity. The mean peak-to-peak amplitudes of motor evoked potential (MEP) were compared. The active motor threshold (AMT) and onset latency for inion BST and ipsilateral BST were also measured and compared.ResultsContralateral BST did not evoke discernible MEPs in most subjects. In 21 subjects (67.7%), ipsilateral BST elicited larger MEPs than inion BST did, and AMT for ipsilateral BST was lower than or equal to the AMT for inion BST in all subjects. Ipsilateral BST elicited shorter latency in such subjects.ConclusionsThe suitable stimulation site for BST differed among subjects. About two-thirds showed larger MEP to ipsilateral BST.SignificanceThese findings might help us to find an efficient stimulation site for BST in each subject.

► We have refined the examination protocol of magnetic brainstem stimulation (BST).
► We revealed that ipsilateral stimulation elicits larger motor evoked potentials (MEPs) than the conventional inion stimulation in nearly two-thirds of healthy subjects.
► Our method will be also beneficial to the procedure of cerebellar inhibition (CBI).