Neuroelectrics has not tested and does not recommend the use of extracephalic references for stimulation protocols.
However, if a researcher or clinician decides to implement this configuration for investigational purposes, the following considerations should be carefully evaluated:
1. Potential for Higher Impedances
Extracephalic montages may result in higher impedance values due to increased inter-electrode distance and tissue variability. This can affect stimulation stability and overall session reliability.
2. Uncertain Current Distribution
The electric field (E-field) distribution in extracephalic configurations is not as extensively characterized as cephalic montages. As a result, unintended cortical or subcortical regions may receive non-targeted stimulation. Some superficial areas may receive limited field intensity, while deeper brain structures could be exposed to higher-than-anticipated E-field strengths.
3. Limited Safety Evidence in Specific Populations
For certain populations, including pregnant women and other vulnerable groups, there is insufficient evidence to fully assess safety in extracephalic stimulation paradigms. Additional caution and ethical review are strongly advised.
Researchers are encouraged to carefully evaluate risk-benefit considerations, perform appropriate modeling when possible, and obtain the necessary ethical and regulatory approvals before implementing extracephalic reference configurations.