Navigated transcranial magnetic stimulation does not decrease the variability of motor-evoked potentials

Jung, Nikolai H.; Delvendahl, Igor; Kuhnke, Nicola G.; Hauschke, Dieter; Stolle, Sabine; Mall, Volker

doi:10.1016/j.brs.2009.10.003

« Previous Next »BRAIN STIMULATION: Basic, Translational, and Clinical Research in Neuromodulation
Volume 3, Issue 2 , Pages 87-94, April 2010

Navigated transcranial magnetic stimulation does not decrease the variability of motor-evoked potentials

Nikolai H. Jung
- Department of Neuropaediatrics and Muscular Disorders, Department of Paediatrics and Adolescent Medicine, University Medical Center Freiburg, Germany
Igor Delvendahl
- Department of Neuropaediatrics and Muscular Disorders, Department of Paediatrics and Adolescent Medicine, University Medical Center Freiburg, Germany
Nicola G. Kuhnke
- Department of Neuropaediatrics and Muscular Disorders, Department of Paediatrics and Adolescent Medicine, University Medical Center Freiburg, Germany
Dieter Hauschke
- Department of Medical Biometry and Medical Informatics, University Medical Center Freiburg, Germany
Sabine Stolle
- Department of Neuropaediatrics and Muscular Disorders, Department of Paediatrics and Adolescent Medicine, University Medical Center Freiburg, Germany
Volker Mall
- Department of Neuropaediatrics and Muscular Disorders, Department of Paediatrics and Adolescent Medicine, University Medical Center Freiburg, Germany
- Correspondence: Prof. Dr. med. Volker Mall, Division of Neuropaediatrics and Muscular Disorders, Department of Paediatrics and Adolescent Medicine, University Medical Center Freiburg, Germany.

Received 6 July 2009; received in revised form 7 October 2009; accepted 7 October 2009. published online 02 November 2009.

Background

One major attribute of transcranial magnetic stimulation (TMS) is the variability of motor-evoked potential (MEP) amplitudes, to which variations of coil positioning may contribute. Navigated TMS allows the investigator to retrieve a stimulation site with an accuracy of 2.5 mm and to retain coil position with low spatial divergence during stimulation.

Objective

The purpose of this study was to investigate whether increased spatial constancy of the coil using a navigational system decreases the variability of MEP amplitudes and increases their reproducibility between different points in time of investigation.

Methods

We investigated eight healthy subjects (mean age 23.8 ± 1.2 years, range 22-25, four women, four men) at three different points in time with and without an optically tracked frameless navigational device, respectively. Input-output curves, motor threshold, and MEP amplitudes were recorded. We calculated the coefficient of variation as statistical parameter of variability. Reproducibility between different sessions was assessed via the MEP amplitude.

Results

The coefficient of variance of MEP amplitudes did not show a distinct difference between navigated and non-navigated TMS in input-output curves. MEP amplitudes, indicating reproducibility, did not significantly differ between sessions with and without navigated TMS, either.

Conclusions

Our results do not support the hypothesis that increased spatial constancy using a navigational system improves variability and reproducibility of MEP amplitudes. Variability of MEPs might mainly be due to not influenceable neurophysiologic factors such as undulant cortical excitability and spinal desynchronization.

Keywords: transcranial magnetic stimulation, navigation, variability