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Localizing Function-specific Targets for Transcranial Magnetic Stimulation in the Absence of Navigation Equipment
Published on: May 23, 2025
Functional localization in the human brain: Gradient-Echo, Spin-Echo, and arterial spin-labeling fMRI compared with
Svenja Diekhoff1, Kamil Uludağ, Roland Sparing
1Max Planck Institute for Neurological Research, Cologne, Germany.
Human Brain Mapping
|June 10, 2010
Summary
This study compared functional MRI (fMRI) sequences for accurately targeting transcranial magnetic stimulation (TMS) of the motor cortex. Alternative fMRI methods localized neural activity closer to optimal TMS sites than standard GRE-BOLD fMRI.
Area of Science:
- Neuroimaging
- Neuroscience
- Biophysics
Background:
- A consistent spatial mismatch exists between transcranial magnetic stimulation (TMS) targets and functional magnetic resonance imaging (fMRI) signals in the primary motor cortex.
- This discrepancy may stem from magnetic susceptibility artifacts around large draining veins in Gradient-Echo blood oxygenation level-dependent (GRE-BOLD) fMRI.
Purpose of the Study:
- To investigate whether alternative fMRI sequences, specifically Spin-Echo (SE-BOLD) and Arterial Spin-Labeling (ASL) assessing cerebral blood flow (ASL-CBF), can localize neural activity closer to optimal TMS positions in the primary motor cortex compared to GRE-BOLD fMRI.
- To compare the spatial accuracy of different fMRI techniques for guiding TMS interventions.
Main Methods:
- Acquired GRE-BOLD, SE-BOLD, and ASL-CBF fMRI data during right thumb abductions in 15 healthy subjects at 3 Tesla.
- Performed neuronavigated TMS at fMRI signal maxima in 12 subjects to measure motor-evoked potentials (MEPs).
- Calculated Euclidean distances between fMRI centers-of-gravity (CoG) and TMS motor mapping CoGs.
Main Results:
- SE-BOLD and ASL-CBF signals peaked at the anterior wall of the central sulcus (Brodmann Area 4), while GRE-BOLD signals were closer to the gyral surface.
- TMS applied at GRE-BOLD maxima yielded higher MEPs, potentially due to stronger electric field strengths.
- While TMS CoGs were anterior to fMRI CoGs, the spatial distances did not significantly differ across the fMRI sequences.
Conclusions:
- Spatial differences between fMRI and TMS in the motor cortex are unlikely solely due to GRE-BOLD fMRI's spatial specificity.
- Other factors, such as TMS-induced electric field interactions with neural tissue, may contribute to these spatial discrepancies.
- Careful consideration of technique-specific differences is crucial when using fMRI coordinates for TMS targeting.
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