The Use of Electronic Coil Location Control for Focal Magnetic Stimulation at the Cervical Level

TITLE
The Use of Electronic Coil Location Control for Focal Magnetic Stimulation at the Cervical Level

SOURCE
Journal of Neuroscience Methods. 328:108444, 2019 12 01.

AUTHORS
Rodionov A; Tolmacheva A; Kirveskari E; Makela JP; Shulga A.

ABSTRACT
Accurate re-positioning of the coil is challenging in magnetic stimulation at the cervical spinal level. The applicability of coil location control for this type of stimulation is unexplored.

NEW METHOD
Utilizing a figure-of-eight coil and anatomy-specific models of the magnetic stimulation system, we developed a novel technique that enables probing corticospinal excitability at the cervical spinal level. Magnetic stimulation was performed in 9 healthy subjects at C2-C6 spinal levels using a figure-of-eight coil and a coil tracking system. MEPs were recorded from the abductor digiti minimi muscle. The functioning of the coil tracking system was tested with an estimated electric field maximum (eEFM) above the C1 cervical level (group 1) and below (group 2). Motor-evoked potential (MEP) reproducibility was assessed with intra-class correlation coefficient (ICC).

RESULTS
The use of coil location control in cervical level focal magnetic stimulation enabled the recording of highly reproducible MEPs. Within one co-registration, the ICC 95% confidence interval (CI) in group 1 was 0.89-0.99 and in group 2 was 0.24-0.85.

COMPARISON WITH EXISTING METHODS AND CONCLUSIONS
This method can be used for accurate maintenance and retrieval of the focal coil position at the cervical level with low spatial variability during stimulation. Existing methodologies employ determination of the coil location based on external landmarks, which makes the procedure cumbersome. This technique can optimize existing stimulation protocols and facilitate development of navigated spinal stimulation.