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Research Objectives
Previous work noted that there are significant variabilities in motor response to
intermittent theta-burst stimulation (iTBS). It is possible this variability results
from individual neuroanatomical differences. The current objective was to investigate
the effect of individual neuroanatomy on first dorsal interosseous (FDI) and biceps
brachii motor evoked potentials (MEPs) in response to iTBS.
Design
Cross-sectional study using a convenience sample.
Setting
Research laboratory.
Participants
Ten healthy individuals (7 females, 23.5 ± 5 years) participated in this study. Participants
completed two iTBS sessions (one each targeting the FDI and biceps cortical hotspots)
and an MRI on separate days.
Interventions
Not applicable.
Main Outcome Measures
MEPs were calculated using data acquired with a Magstim Super Rapid2 Plus1 stimulator
via a 70 mm double air film coil to the primary motor cortex and electromyography
signals were measured from dominant FDI and biceps. Head models were generated from
T1 & T2 weighted MRI. Diffusion tensor imaging was used to determine fiber tract geometry
for FDI and biceps corticospinal tracts. We then established neuroanatomical parameters
including: fiber tract surface area (FTSA), tract fiber count (TFC), and brain scalp
distance (BSD). Cortical electric field strength (EFS) was calculated using simulated
stimulation of head models and finite element analysis.
Results
For the FDI, there was no effect of iTBS (p = 0.223) but individual changes in corticomotor
excitability scaled with stimulation type and resting motor potential (p < 0.001),
EFS (p = 0.001), BSD (p = 0.004), and FTSA (p = 0.011). iTBS had a faciliatory response
on the biceps and was dependent on FTSA (p < 0.001) and TFC (p < 0.001).
Conclusions
Our results show that MRI-based measures of neuroanatomy, specifically cortical architecture
and tract anatomy, impact how the motor system responds to iTBS, subject to target-specific
cortical control organization. MRI-based modeling of individual neuroanatomy may be
a useful approach in selection of motor targets when designing iTBS-based therapies.
Author(s) Disclosures
None.
Keywords
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Copyright
© 2022 Published by Elsevier Inc.
