The Influence of Grey and White Matter Volume on the Induced Electric Field of the Quadruple Butterfly Coil for Transcranial Magnetic Stimulation*

Transcranial Magnetic Stimulation (TMS) is a neuromodulation technique that non-invasively activates neurons in the brain. During TMS, time-varying magnetic field is delivered to the brain that induces an electric field which, at sufficient levels, causes neurons to depolarize.

One of the challenges in the development of TMS therapy is the ability to deliver a focused electric field to a targeted region in the brain. The Quadruple Butterfly Coil (QBC) is a novel coil design that significantly increases the focality of the induced electric field compared to the commonly used Figure-of-Eight coil.

Research has shown that the grey matter (GM) and white matter (WM) volume are significant anatomical variations in the human brain.

We investigated the relationship between the intensity of the induced E field and the GM and WM volumes when stimulated by the QBC coil. Simulations were run using Sim4Life software on head models derived from magnetic resonance imaging (MRI) scans of 10 healthy subjects and 10 subjects diagnosed with a neurodegenerative disease.