The H-coil was compared to a regular figure-8 coil in 6 healthy volunteers by measuring thresholds for activation of the abductor pollicis brevis (APB) representation in the motor cortex as a function of distance from each of the coils.
The rate of decrease in the coil intensity as a function of distance is markedly slower for the H-coil. The motor cortex could be activated by the H-coil at a distance of 5.5 cm compared to 2 cm with the figure-8 coil.
The present study indicate that the H-coil is likely to have the ability of deep brain stimulation and without the need of increasing the intensity to extreme levels that would cause a much greater stimulation in cortical regions.
The ability of non-invasive deep brain stimulation potentially opens a wide range of both research and therapeutic applications.