The interindividual variability of transcranial magnetic stimulation effects: Implications for diagnostic use in movement disorders

A large number of methods have been described that use transcranial magnetic stimulation to probe the physiology of the human motor cortex. Since the 1990s, hundreds of papers have used them to investigate neurophysiological signatures of different types of movement disorders. However, in recent years there has been increasing recognition of the interindividual variability of these measures and a focus on estimating their reliability and reproducibility. Although this work has been carried out in healthy individuals, it is highly relevant to movement disorders because it may impact the validity of some accepted ("canonical") neurophysiological biomarkers. The aim of this review is to reexamine the diagnostic usefulness of transcranial magnetic stimulation methods in movement disorders in the context of present knowledge of methodological variability.