Transcranial Magnetic Stimulation: Principles and Applications

Transcranial magnetic stimulation (TMS) is a noninvasive method for focal brain stimulation, with applications in research, diagnostics, and treatment. In basic research, TMS can help establish a causal link between a brain circuit and a behavior. Clinically, repetitive TMS can alter the long-term excitability of specific brain regions to treat psychiatric and neurological disorders. This chapter aims to support engineers and researchers to understand and innovate TMS technology. It introduces the basics of TMS spanning engineering, physics, biophysics, paradigms, and applications. First, the principles of TMS devices are explained including the electrical circuit topologies and efficiency of the pulse generator as well as the design of the stimulation coil. Ancillary effects such as heating, electromagnetic forces, and interactions with other devices are considered. Then, the underlying physics and its modeling are presented, including the magnetic field of the coil and the impact of the subject’s head on the induced electric field. This is followed by a description of the biophysics of neuronal activation due to TMS, including the cable equation, leaky integrate-and-fire neural membrane dynamics, and morphologically realistic neuron models. Various methods to measure the responses to TMS are summarized, spanning observations of behavior, electromyography, epidural recordings, electroencephalography, functional near-infrared spectroscopy, functional magnetic resonance imaging, and positron emission tomography. The chapter concludes with an overview of stimulation paradigms encompassing single-pulse, paired-pulse, and repetitive TMS, along with their applications in basic research and the clinic. The chapter includes ten problems that cover the presented material.