Transcranial magnetic stimulation coil with electronically switchable active and sham modes.

Area of Science:

• Neuroscience
• Biomedical Engineering
• Medical Physics

Background:

• Blinded studies using transcranial magnetic stimulation (TMS) necessitate reliable sham conditions.
• Existing sham methods for TMS have limitations, including residual brain electric fields and inadequate sensory simulation.

Purpose of the Study:

• To introduce and evaluate a novel quadrupole TMS coil configuration for improved sham conditions in blinded studies.
• To compare the electric field characteristics of the quadrupole coil in sham mode against a conventional figure-8 coil.

Main Methods:

• Development of a quadrupole TMS coil capable of electronic switching between active and sham modes.
• Characterization of electric field properties in both active and sham modes.
• Comparison of electric field penetration depth, focality, and intensity with existing sham methods.

Main Results:

• The quadrupole coil in active mode exhibits electric field characteristics similar to a standard figure-8 coil.
• In sham mode, the quadrupole coil demonstrates significantly reduced electric field penetration (50% less) and improved focality (97% more focal).
• The sham mode of the quadrupole coil produces a less intense field (35% less) in the brain and more closely mimics active TMS scalp electric field characteristics.

Conclusions:

• The proposed quadrupole TMS coil offers a superior sham condition for blinded studies.
• This coil design addresses limitations of current sham methods, potentially increasing the validity and reliability of TMS research.
• The enhanced sham properties contribute to more robust experimental designs in transcranial magnetic stimulation.