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Research Objectives
Previous research has demonstrated that anatomical complexities of cortical regions
determine transcranial magnetic stimulation (TMS) induced electric fields in the brain,
which impact the response to TMS-based therapies. The current objective was to investigate
the effect of individual neuroanatomy on first dorsal interosseous (FDI) and biceps
brachii resting motor thresholds (RMT) in response to TMS.
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. Each
participant completed two TMS sessions (one each targeting the FDI and biceps cortical
hotspots) and an MRI of the head on separate days.
Interventions
Not applicable.
Main Outcome Measures
RMTs were determined using a Magstim Super BiStim stimulator via a 70 mm figure-of-eight
coil to the left primary motor cortex and electromyography signals were measured from
right FDI and biceps. Head models were generated based on T1 & T2 weighted MRI, while
diffusion tensor imaging was used to determine fiber tract geometry for FDI and biceps
corticospinal tracts. Via the models, we 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, RMT was dependent on the interaction between individually modeled parameters:
1) EFS and FTSA (p = 0.036), and 2) EFS and TFC (p = 0.004). For the biceps, RMT was
dependent on the interaction between 1) EFS and FTSA (p = 0.022) and 2) EFS and BSD
(p = 0.010).
Conclusions
Our study results show that MRI-based measures of neuroanatomy, specifically cortical
architecture and tract anatomy, differentially impact how the motor system responds
to TMS. MRI-based modeling of individual neuroanatomy may be a useful approach to
select appropriate motor targets when designing TMS based therapies.
Author(s) Disclosures
None.
Keywords
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© 2022 Published by Elsevier Inc.
