How to include the variability of TMS responses in simulations: a speech mapping case study

Area of Science:

• Computational neuroscience
• Neuroimaging
• Electrophysiology

Background:

• Transcranial magnetic stimulation (TMS) is used for mapping speech-related brain areas preoperatively.
• Variability in TMS responses necessitates a deeper understanding of underlying neural mechanisms.
• Neuronavigation systems guide TMS coil placement but do not fully account for response variability.

Observation:

• Four cases with minor coil position/orientation perturbations during a speech mapping experiment were analyzed.
• One case (E) resulted in a naming error, while others (NE_{A, B, C}) showed no disruption.
• Realistic anisotropic head models and diffusion tensor imaging (DTI)-based tractography were used for analysis.

Findings:

• Induced electric field distributions showed minimal differences across cases.
• Membrane potential computations revealed distinct white matter tract activation patterns.
• A tract connecting Broca's and Wernicke's areas was activated only in the error case (E).

Implications:

• Subject-specific modeling of electromagnetic fields and neuronal activity is crucial for understanding TMS variability.
• Computational models can reveal how subtle coil variations impact neural network activation.
• Further research is needed to refine neural models, incorporating synapses and network connections for enhanced accuracy.