The relationship between TMS measures of functional properties and DTI measures of microstructure of the corticospinal tract.
BACKGROUND
Recently, a link between resting motor threshold (RMT) and local tissue microstructure, as indexed by fractional anisotropy (FA), was demonstrated in large parts of white matter. However, regions showing such correlations were generally found outside of the corticospinal tract (CST). Therefore, the question arises whether other electrophysiologic measurements could be more locally related to microstructural properties of the CST. In this study, we explored the relationship between such measurements and regional FA in a group of healthy volunteers.


OBJECTIVE
We hypothesized that RMT might be more related to an overall susceptibility of white matter to TMS, whereas other electrophysiologic markers might be more specifically related to properties of the CST only.


METHODS
Thirty-seven subjects were included. We studied RMT, active motor threshold (AMT), intensity to evoke a motor-evoked potential (MEP) of 1 mV (S1mV), MEP input-output curve (IO-curve), and central motor conduction time (CMCT) using transcranial magnetic stimulation, and FA of the corticospinal tract using diffusion tensor magnetic resonance imaging. We performed voxel-wise and TBSS correlation analysis between these electrophysiologic measurements and FA. In addition, we tested for significant correlation between these parameters and mean diffusivity (MD).


RESULTS
On voxel-wise analysis, we did not detect significant correlations between any electrophysiologic parameter (RMT, AMT, S1mV, IO curve slope, CMCT) and FA. With TBSS, we detected correlations between FA and bilateral AMT, as well as left-hemispheric S1mV, but these correlations were found in locations unlikely to contribute to motor pathways.


CONCLUSIONS
Although a relationship between structure and function has been shown in many other regions of the brain, it seems to be much more challenging to demonstrate such a relationship in the CST of healthy subjects.
Department of Neurology, Goethe-University Frankfurt, Frankfurt, Germany.
Annemarie
A
Hübers
Department of Neurology, Goethe-University Frankfurt, Frankfurt, Germany.
Johannes C
JC
Klein
Department of Neurology, Goethe-University Frankfurt, Frankfurt, Germany.
Jun-Suk
JS
Kang
Department of Neurology, Goethe-University Frankfurt, Frankfurt, Germany.
Rüdiger
R
Hilker
Department of Neurology, Goethe-University Frankfurt, Frankfurt, Germany. Electronic address: u.ziemann@em.uni-frankfurt.de.
Ulf
U
Ziemann
D000328:Adult; D000368:Aged; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000166:cytology* / Q000502:physiology*; D011712:Pyramidal Tracts / Q000166:cytology* / Q000502:physiology*; D013223:Statistics as Topic; D050781:Transcranial Magnetic Stimulation / Q000379:methods*