Grundlagen und Anwendung der Transkraniellen Magnetstimulation

ZusammenfassungDer Beitrag schildert technische und physiologische Grundlagen der transkraniellen Magnetstimulation, Kontraindikationen und Nebenwirkungen sowie Einsatzmöglichkeiten zu diagnostischen und therapeutischen Zwecken.

SummaryTranscranial magnetic stimulation (TMS) was introduced in 1985 and has become an important tool for the diagnosis of central motor pathway lesions and for the exploration of motor excitability in health and disease. Moreover, it gains an increasing relevance as a therapeutic tool.The current flow in the coil induces a short-lasting magnetic field which evokes an electrical current in superficial parts of the brain. The induced current in the brain stimulates horizontally oriented neurons and activates pyramidal cells trans-synaptically. A single TMS pulse evokes a series of neuronal responses (D wave and I waves) which activate alpha motoneurons on the level of the spinal cord. Finally, the muscle twitch evoked by TMS over the motor cortex can be recorded from the target muscle (motor evoked potential, MEP). MEP latency and amplitude are the most relevant parameters for examining the integrity of the corticospinal tract. Specific TMS techniques such as paired pulse stimulation, recording of the silent period, and collection of stimulus-response curves allow the investigation of inhibitory and excitatory properties of the motor system under different conditions, e.g. after drug intake and in various diseases affecting the central nervous system. Repetitive TMS modulates motor excitability and is used for therapeutic purposes in psychiatric and neurological disorders.