Construction and Evaluation of Rodent-Specific rTMS Coils.

Area of Science:

• Neuroscience
• Biomedical Engineering

Background:

• Rodent models are essential for understanding transcranial magnetic stimulation (TMS) mechanisms of plasticity.
• Previous rodent TMS coils offered focal stimulation but lacked intensity.
• Higher intensity TMS is needed to explore cellular and molecular changes induced by TMS.

Purpose of the Study:

• To design and characterize novel TMS coils for rodent studies.
• To achieve higher stimulation intensities with maintained spatial resolution.
• To investigate the effects of novel coil-generated fields on cortical excitability.

Main Methods:

• Two novel circular TMS coils (8 mm outer diameter) were constructed: one air-core and one pure iron-core.
• Peak magnetic field strength, focality, coil temperature, and magnetic field stability were measured.
• Finite element modeling was used to simulate electric fields in a rat brain model.
• Repetitive TMS (rTMS) was applied to the motor cortex of anesthetized rats.

Main Results:

• The iron-core coil achieved higher peak magnetic field strength (120 mT) than the air-core coil (90 mT).
• The iron-core coil showed reduced focality compared to the air-core coil.
• Finite element modeling predicted electric fields of 85 V/m (skull) and 12.7 V/m (brain) at 10 Hz rTMS with the iron-core coil.
• 10 Hz rTMS with the iron-core coil significantly increased motor evoked potential amplitudes in rats.

Conclusions:

• Novel TMS coils provide higher magnetic field intensities for rodent models.
• These coils can alter cortical excitability, evidenced by increased motor evoked potentials.
• The developed coils offer a valuable tool for investigating rTMS-induced plasticity mechanisms in experimental settings.