Double-Pulse Magnetic Brain Stem Stimulation: Mimicking Successive Descending Volleys

Abstract

Matsumoto H, Hanajima R, Hamada M, Terao Y, Yugeta A, Inomata-Terada S, Nakatani-Enomoto S, Tsuji S, Ugawa Y. Double-pulse magnetic brain stem stimulation: mimicking successive descending volleys. J Neurophysiol 100: 3437-3444, 2008. First published October 15, 2008 doi:10.1152/jn.90751.2008. Magnetic stimulation with a double-cone-coil over the back of the head activates the motor tracts at the level of pyramidal decussation (brain stem stimulation [BST]). However, single-pulse BST (single BST) sometimes cannot elicit motor-evoked potentials (MEPs) in patients with corticospinal tract involvement. We developed a technique using double-pulse BST (double BST) to elicit MEPs even in patients whose threshold is abnormally elevated. Subjects were 11 healthy volunteers and 12 patients with corticospinal tract involvement in whom single BST evoked no discernible MEP. Double BST was performed at the intensities of resting and active motor threshold for single BST; MEPs were recorded from the first dorsal interosseous muscle. Interstimulus intervals (ISIs) between two pulses were 1.5, 2, 3, 5, and 10 ms in healthy subjects. Double BST enlarged MEPs at ISIs of 1.5-5 ms with a peak at 2 ms in the relaxed condition, but not in the active condition. At an ISI of 2 ms in the relaxed condition, the MEP amplitude was 15 times as large as that to single BST in relaxed muscles. The onset latency of the enlarged MEP from the second pulse in relaxed muscles was the same as that by single BST in active muscles. Double BST at a 2-ms interval elicited MEPs in eight patients. Double BST can enhance MEPs probably by temporal summations of excitatory postsynaptic potentials at the spinal motoneurons. Using this new technique, we can obtain more information about the central motor conduction even when single BST fails to elicit any MEP.

The impact of pulse timing on cortical and subthalamic nucleus deep brain stimulation evoked potentials

“…Our understanding of the mechanism of action of DBS remains poorly understood and attempts at improving DBS or translating it to other disease modalities could benefit from a better understanding of how to effectively modulate circuit dynamics. Manipulating pulse timing and capitalizing on the effects of temporal summation provides a means of enhancing circuit engagement without increasing stimulation amplitude and current spread, which can be associated with undesirable side-effects (Matsumoto et al, 2008 ). Furthermore, a better understanding of temporal dynamics may improve our ability to develop new technology that targets BGTC circuit modulation to deliver therapeutic benefit and treat disease.…”

Temporal Profile and Limb-specificity of Phasic Pain-Evoked Changes in Motor Excitability

“…The recording of MEPs elicited by transcutaneous electrical stimulation of the cortico-spinal tract at cervico-medullary level could be an interesting mean (Taylor, 2006). However, cervico-medullary MEPs are difficult to obtain in relaxed subjects (Matsumoto et al, 2008). We attempted to record these responses in pilot experiments, but failed to obtain consistent responses compatible with the objective of assessing how they are modulated by a preceding laser stimulus.…”

Central and Peripheral Motor Conduction Studies by Single-Pulse Magnetic Stimulation

“…In such cases, double-pulse stimulation at the foramen magnum might elicit clear MEPs by artificially inducing the temporal summations of EPSPs in the spinal MNs. 51 52 …”