Transcranial Magnetic Stimulation

Abstract Transcranial magnetic stimulation (TMS) is gaining increasing prominence as a non‐invasive neuromodulation technique for the treatment of neurological and psychiatric conditions. Repetitive transcranial magnetic stimulation (rTMS) has therapeutic potential for a range of psychiatric disorders (e.g. depression, schizophrenia) as well as neurological disorders such as Parkinson's disease. The approach has advantages over pharmacological or electroconvulsive therapy due to its painlessness and limited side effects. The magnitude, duration and direction (increase or decrease) of TMS‐induced changes in brain excitability vary depending on the strength and timing of stimulation and the interaction of stimulation coil geometry with brain structures. The outcomes of TMS stimulation can also depend on the characteristics (e.g. age, exercise status) of the individual being treated. Despite increasing clinical use of rTMS, the cellular and network mechanisms underlying the clinical application of rTMS remain elusive and will need to be better understood to enable optimisation of clinical outcomes. Key Concepts Transcranial magnetic stimulation is a non‐invasive brain stimulation technique that uses a varying magnetic field to induce currents in the cortex and modulate brain function. Single TMS pulses can be used to evoke immediate sensory or motor responses and test the speed or efficacy of conduction in a particular neural pathway. Repetitive transcranial magnetic stimulation (rTMS) produces more subtle modulation of brain function that lasts beyond the end of stimulation. Common rTMS protocols include regular trains of pulses at different frequencies (usually 1 or 10 Hz) or complex pulse trains that mimic endogenous patterns of activity in different brain regions (e.g. continuous and intermittent theta burst stimulation, biomimetic high‐frequency stimulation). rTMS has been found to induce plasticity in the brain, with higher frequency (10–20 Hz) stimulus patterns generally associated with strengthening of cortical pathways, whereas low frequency (1 Hz) patterns usually depress the activity of a pathway. rTMS is established as an effective therapy for major depression and for neuropathic pain and shows promise in treating some symptoms of stroke, Parkinson's Disease and schizophrenia. Optimisation and expansion of the therapeutic utility of rTMS will require a better scientific understanding of the physiological mechanisms by which pulsed magnetic fields modulate the function of and interactions between neurons.