Anatomical variability predicts individual differences in transcranial electric stimulation motor threshold

Area of Science:

• Neuroscience
• Biomedical Engineering
• Medical Physics

Background:

• Current electroconvulsive therapy (ECT) uses fixed high current amplitudes, potentially leading to suboptimal stimulation.
• Individual anatomical variability necessitates personalized approaches for effective and safe ECT.

Purpose of the Study:

• To estimate the electric field (E-field) neural activation threshold for ECT.
• To investigate if transcranial electric stimulation (TES) motor threshold (MT) predicts individual ECT current requirements.
• To assess the role of anatomical variability in determining individual TES MT.

Main Methods:

• Computed E-field distribution using subject-specific finite element head models in nonhuman primates (NHPs).
• Measured MT in NHPs using TES applied through ECT electrodes.
• Correlated individual MT with anatomical measurements and simulated E-field ratios.

Main Results:

• Estimated neural activation threshold at 0.45 ± 0.07 V/cm for a 0.2 ms pulse width.
• Individual MT significantly correlated with electrode-to-cortex distance (R(2)=.96) and simulated electrode-current/E-field ratio (R(2)=.95).
• Anatomical measurements and computational models accurately predicted individual current requirements.

Conclusions:

• Individualized TES-based MT determination can predict optimal ECT current amplitude.
• This approach allows for stimulation closer to the neural activation threshold, accounting for anatomical differences.
• Findings support novel, noninvasive ECT dosing paradigms using realistic human head models.