Design of coils with potential use in transcranial magnetic stimulation

Transcranial magnetic stimulation (TMS) is a new tool for neuroscience allowing for non-invasive stimulation of neurons. It has shown potential for treating several neuropsychiatric disorders such as hypokinetic movement, anxiety, schizophrenia and depression. It has also been used as a brain mapping tool. By inducing electric currents with a time-varying, strong magnetic field, TMS can modulate the neuronal circuits associated with these disorders. This modulation should be spatially-selective in order to minimize the stimulation of neighboring neuronal circuits. The improvement of this selectivity is then a key issue for this technology. We present an innovative coil configuration with two additional coils allowing for a significant improvement in spatial selectivity as compared to standard configurations. We simulated this coil configuration both by analytic computation of the Biot-Savart law. The results show one sharper, more intense spatial field peak resulting in improved field localization for this new coil configuration. The power losses, a very important parameter for actual implementation, were also computed using the analytical method and a finite element method. The results obtained from both methods are in agreement.