Transcranial magnetic stimulation in hereditary ataxias: diagnostic utility, pathophysiological insight and treatment

Transcranial magnetic stimulation (TMS) is a non-invasive method for stimulation and modulation of the human brain allowing the study of corticospinal tract function, facilitation and inhibition in neural networks and brain plasticity (Wassermann et al., 2008). TMS is based on the fundamental principles of electromagnetic induction: a brief current in the stimulating coil induces a magnetic field that in turn induces an electric current in brain regions underneath the stimulating coil. In motor cortex, this leads to action potentials in corticospinal cells and multiple descending corticospinal volleys that synapse in spinal gray matter onto alpha-motoneurons, causing in turn action potentials and, finally, activation of muscles which can be recorded as motor evoked potentials (MEPs) by surface electromyography (Hallett, 2007; Kobayashi and Pascual-Leone, 2003) (Fig.

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