My Editor’s Choice

Professor Ulf Ziemann,Editor-in-Chief, Clinical Neurophysiology

Professor Ulf Ziemann
Editor-in-Chief, Clinical Neurophysiology

The Editor’s Choice—

Transcranial magnetic stimulation of the brain: What is stimulated?— A consensus and critical position paper

Clinical Neurophysiology Volume 140 (August 2022)

Siebner HR, Funke K, Aberra AS, Antal A, Bestmann S, Chen R, Classen J, Davare M, Di Lazzaro V, Fox PT, Hallett M, Karabanov AN, Kesselheim J, Beck MM, Koch G, Liebetanz D, Meunier S, Miniussi C, Paulus W, Peterchev AV, Popa T, Ridding MC, Thielscher A, Ziemann U, Rothwell JC, Ugawa Y. Transcranial magnetic stimulation of the brain: What is stimulated?—A consensus and critical position paper. Clinical Neurophysiology 2022; 140: 59–97

Transcranial magnetic stimulation (TMS) is now available for almost 40 years, since the original presentation by Professor Anthony Barker in 1985. It has developed into the most widely used tool to perturb the human brain non-invasively for understanding brain function, and for therapeutic modification of dysfunctional brain circuits. Approximately 25,000 TMS studies have been published. Astonishingly, it is still not fully understood how TMS activates the brain and what is stimulated.

A globally distributed group of leading TMS experts has now produced a comprehensive consensus and critical position paper to address this question, with the following main points: TMS likely targets axons of excitatory and inhibitory neurons. Excitation occurs depending on axon geometry, myelination and spatial relation to the induced electric field. Primary target are axonal terminals in the crown top and lip of cortical gyri, and bends of myelinated axons in the juxtacortical white matter. Excitation propagates ortho- and antidromically and causes secondary excitation of connected local and distant neuronal populations, depending on functional state of the stimulated target area and network. TMS inevitably causes substantial direct co-stimulation of auditory and somatosensory inputs. This complexity of the TMS response warrants cautious interpretation of its physiological and behavioral consequences. In summary, while TMS is an extremely important tool in clinical neurophysiology and the neurosciences, we still need to advance our mechanistic understanding of how TMS activates the human brain to facilitate thorough therapeutic and scientific applications.

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