Transcranial Magnetic Stimulation (TMS)
Transcranial magnetic stimulation (TMS) is a neurostimulation and neuromodulation technique, based on the principle of electromagnetic induction of an electric field in the brain. This field can be of sufficient magnitude and density to depolarize neurons, and when TMS pulses are applied repetitively they can modulate cortical excitability, decreasing or increasing it, depending on the parameters of stimulation, even beyond the duration of the train of stimulation. This has behavioral consequences and therapeutic potential.The last decade has seen a rapid increase in the applications of TMS to study cognition, brain-behavior relations and the pathophysiology of various neurologic and psychiatric disorders (Wassermannn and Lisanby, 2001; Kobayashi and Pascual-Leone, 2003; Gershon et al., 2003; Tassinari et al., 2003; Rossi and Rossini, 2004; Leafaucheur, 2004; Hoffman et al., 2005; Couturier, 2005; Fregni et al., 2005a,b; Hallett, 2007; George et al., 2007; Málly and Stone, 2007; Rossini and Rossi, 2007; Devlin and Watkins, 2007; Ridding and Rothwell, 2007).
In addition, evidence has accumulated that demonstrates that TMS provides a valuable tool for interventional neurophysiology applications, modulating brain activity in a specific, distributed, cortico-subcortical network so as to induce controlled and controllable manipulations in behavior.
We are honored to have hosted, on behalf of the International Federation of Clinical Neurophysiology (IFCN), the consensus conference on March 7–9, 2008 in order to update the previous safety guidelines for the application of transcranial magnetic stimulation (TMS) in research and clinical settings [See article here]. A meeting for an update of the guidelines will be held in Siena on October 2018
Transcranial Electric Stimulation (tES)
The Transcranial Electric Stimulation (tES) technique (Nitsche et al., 2008; Priori, 2003) involves the application of weak electrical currents (~1-2 mA) directly to the head for several minutes (~5-30 minutes). The stimulation is delivered by a battery-driven current stimulator through a pair of electrodes. These currents generate an electrical field that modulates neuronal activity according to the modality of the application, which can be direct (transcranial Direct Current Stimulation, tDCS), random noise (transcranial Random Noise Stimulation, tRNS) or alternating (transcranial Alternating Current Stimulation, tACS). tES induces a polarization that is too weak to elicit action potentials in cortical neurons. However, it effectively modifies the evoked cortical response to afferent stimulation as well as the postsynaptic activity level of cortical neurons, presumably by inducing a shift in intrinsic neuronal excitability (as shown in tDCS studies on animals, Bindman et al., 1964; Purpura and McMurtry, 1965).
Changes induced by a single application of tDCS are reversible (analogously than TMS), last from a few minutes to more than an hour, and are dependent upon N-methyl D-aspartate (NMDA) (Ridding and Ziemann, 2010). TMS and tDCS results are similar in regard to involved neuromodulators: tDCS effects are not observed after administration of an NMDA receptor antagonist (Nitsche et al., 2003). Blocking of Na+ channels and stabilizing membrane potential abolishes both long- and short-term anodal stimulation effects (Nitsche et al., 2003).
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