The mechanism of action of TMS is still not fully understood however the response to therapy is indisputable and has consistently demonstrated results in the majority of research being done in the field. The TMS electromagnetic pulse is generated by electrical current running through the TMS coil which by method of induction (Faraday’s law) generates a magnetic field perpendicular to the coil. This magnetic field passes through the skull unimpeded and in turn generates a corresponding electric field in the brain also by method of induction. This electric field is conducted by neural pathways under the coil in a somewhat unpredicable way as brain tissue is not uniform and anatomy varies from individual to individual. Neurons are conductive just like the rest of the nerve fibers in your body. Depending on the protocol used and frequency of TMS pulse entire regions of neurons under the coil can either become excited or inhibited. In Depression, neurons in the left DLPFC (Dorsolateral prefrontal cortex) are targeted by the coil with an excitatory protocol (FDA cleared). Subtle changes in brain state as a result of TMS can last up to several hours and even days after a TMS session has been performed. If done repetitively over a 3-6 week period TMS induces structural changes in the brain where the coil has been placed. Increased gray matter density and blood flow to the part of the brain stimulated have all been clearly demonstrated in research using MRI brain scans.
Not everyone responds to TMS therapy for Depression but most people will. Many clinicians see a 70% – 80% response rate in their patient population. At least half of these responders will achieve full remission. In the literature TMS response rates when treating Depression have been shown to be at least as effective as medications used to treat Depression. And of course without all the side effects that medications bring.
Many patients say they can still feel benefit from TMS therapy years after their first round of TMS treatment. The effect appears to be quite durable especially in people who respond well to treatment. In some cases patients will go back for a few TMS maintenance sessions 3-6 months after their initial treatment.