Long-lasting effects of transcranial static magnetic field stimulation on motor cortex excitability

• Main Authors: Michele Dileone, Laura Mordillo-Mateos, Antonio Oliviero, Guglielmo Foffani
• Format: Article
• Language: English
• Published: Elsevier 2018-07-01
• Series: Brain Stimulation
• Subjects: Transcranial magnetic stimulation; tSMS; MEP; SICF; SICI; LTD
• Online Access: http://www.sciencedirect.com/science/article/pii/S1935861X18300688

Background: Transcranial static magnetic field stimulation (tSMS) was recently added to the family of inhibitory non-invasive brain stimulation techniques. However, the application of tSMS for 10–20 min over the motor cortex (M1) induces only short-lasting effects that revert within few minutes. Objective: We examined whether increasing the duration of tSMS to 30 min leads to long-lasting changes in cortical excitability, which is critical for translating tSMS toward clinical applications. Methods: The study comprised 5 experiments in 45 healthy subjects. We assessed the impact of 30-min-tSMS over M1 on corticospinal excitability, as measured by the amplitude of motor evoked potentials (MEPs) and resting motor thresholds (RMTs) to single-pulse transcranial magnetic stimulation (TMS) (experiments 1–2). We then assessed the impact of 30-min-tSMS on intracortical excitability, as measured by short-interval intracortical facilitation (SICF) and short-interval intracortical inhibition (SICI) using paired-pulse TMS protocols (experiments 2–4). We finally assessed the impact of 10-min-tSMS on SICF and SICI (experiment 5). Results: 30-min-tSMS decreased MEP amplitude compared to sham for at least 30 min after the end of the stimulation. This long-lasting effect was associated with increased SICF and reduced SICI. 10-min-tSMS –previously reported to induce a short-lasting decrease in MEP amplitude– produced the opposite changes in intracortical excitability, decreasing SICF while increasing SICI. Conclusions: These results suggest a dissociation of intracortical changes in the consolidation from short-lasting to long-lasting decrease of corticospinal excitability induced by tSMS. The long-lasting effects of 30-min-tSMS open the way to the translation of this simple, portable and low-cost technique toward clinical trials.