Transcranial magnetic stimulation (TMS) therapy is based on the principle of electromagnetic induction discovered by Michael Faraday in 1831. According to this principle, a magnetic field can be induced when passing an electrical current through a coil of wire. During a TMS treatment, an insulated magnetic coil is placed over the scalp, to reach the dorso-lateral prefrontal cortex, a brain region involved in depression. The TMS device discharges an electrical current into the coil, which creates a strong magnetic field (similar to the strength of an MRI device 1.5 – 3 Tesla). This magnetic field (and not the current directly) passes through the skull inducing a flow of current in the brain, causing brain cells to fire.