Transcranial static magnetic field stimulation of the human motor cortex

Abstract

Non-technical summary Non-invasive neuromodulation of the human brain -with pulsed magnetic fields or small direct currents -is becoming increasingly popular for treating a variety of neurological and neuropsychiatric disorders. In the present work we investigated in healthy humans the possibility of a non-invasive modulation of motor cortex excitability by the application of static magnetic fields through the scalp. We found that transcranial static magnetic field stimulation (tSMS) can reduce the excitability of the motor cortex for a period that outlasts the time of the application of the magnetic field. Moreover, we demonstrated that these excitability changes take origin at the cortical level. These results suggest that tSMS using small static magnets may be a promising tool to modulate cerebral excitability in a non-invasive, painless and reversible way.Abstract The aim of the present study was to investigate in healthy humans the possibility of a non-invasive modulation of motor cortex excitability by the application of static magnetic fields through the scalp. Static magnetic fields were obtained by using cylindrical NdFeB magnets. We performed four sets of experiments. In Experiment 1, we recorded motor potentials evoked by single-pulse transcranial magnetic stimulation (TMS) of the motor cortex before and after 10 min of transcranial static magnetic field stimulation (tSMS) in conscious subjects. We observed an average reduction of motor cortex excitability of up to 25%, as revealed by TMS, which lasted for several minutes after the end of tSMS, and was dose dependent (intensity of the magnetic field) but not polarity dependent. In Experiment 2, we confirmed the reduction of motor cortex excitability induced by tSMS using a double-blind sham-controlled design. In Experiment 3, we investigated the duration of tSMS that was necessary to modulate motor cortex excitability. We found that 10 min of tSMS (compared to 1 min and 5 min) were necessary to induce significant effects. In Experiment 4, we used transcranial electric stimulation (TES) to establish that the tSMS-induced reduction of motor cortex excitability was not due to corticospinal axon and/or spinal excitability, but specifically involved intracortical networks. These results suggest that tSMS using small static magnets may be a promising tool to modulate cerebral excitability in a non-invasive, painless, and reversible way.

Cerebellar transcranial static magnetic field stimulation transiently reduces cerebellar brain inhibition

“…However, rTMS and tDCS are not comfortable for subjects submitted to these techniques (Hardwick et al, 2014). Recently, transcranial static magnetic field stimulation (tSMS), a technique that is comfortable for the subject (Oliviero et al, 2011) and safe for healthy humans (Oliviero et al, 2015), was developed. With this method, stimulation is produced by placing a small neodymium magnet over the human motor cortex, which can modulate the excitability of M1 (Oliviero et al, 2011).…”

“…Recently, transcranial static magnetic field stimulation (tSMS), a technique that is comfortable for the subject (Oliviero et al, 2011) and safe for healthy humans (Oliviero et al, 2015), was developed. With this method, stimulation is produced by placing a small neodymium magnet over the human motor cortex, which can modulate the excitability of M1 (Oliviero et al, 2011). tSMS over the motor cortex transiently inhibits motor evoked potentials (MEPs), but does not modulate the resting motor threshold (rMT) (Rosen, 2003), indicating that tSMS may not affect the membrane excitability of pyramidal neurons, but may instead induce changes at synaptic level.…”

Safety Study of Transcranial Static Magnetic Field Stimulation (tSMS) of the Human Cortex

“…The rationale for using EEG recordings to assess NIBS safety is because of the increased risk of seizures with protocols that increase cortical excitability. tSMS was shown to reduce cortical excitability both in the sensorimotor cortex of humans [2,3,24], and in the visual cortex of cats and monkeys [23]. Decreased cortical excitability should reduce rather than increase the risk of seizures.…”

“…Repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS) are commonly used for NIBS in humans and animals. Recently we described that the application of transcranial static magnetic field stimulation (tSMS) in humans reduces the output of motor cortex -tested using TMS -for a few minutes after the end of stimulation [2]. Reduced motor output after tSMS can be explained by reduced motor cortex excitability.…”

Transcranial static magnetic field stimulation - new non-invasive brain stimulation tool

“…Current research has reported that the human motor cortex can be modulated by the application of static magnetic fields (SMFs) through the scalp 3) . Oliviero et al showed that 10 min of transcranial static magnetic field stimulation (tSMS) using a powerful cylindrical neodymium, iron and boron (NdFeB or "neo") magnet can reduce the amplitude of motor evoked potentials (MEPs) for a few minutes after magnet removal 3) . In addition, they demonstrated that the polarity of the SMFs was not an important factor for neuromodulation, and that tSMS was not directly associated with induced electric currents.…”