Static Magnetic Field Stimulation over the Visual Cortex Increases Alpha Oscillations and Slows Visual Search in Humans

Abstract

Transcranial static magnetic field stimulation (tSMS) was recently introduced as a promising tool to modulate human cerebral excitability in a noninvasive and portable way. However, a demonstration that static magnetic fields can influence human brain activity and behavior is currently lacking, despite evidence that static magnetic fields interfere with neuronal function in animals. Here we show that transcranial application of a static magnetic field (120 -200 mT at 2-3 cm from the magnet surface) over the human occiput produces a focal increase in the power of alpha oscillations in underlying cortex. Critically, this neurophysiological effect of tSMS is paralleled by slowed performance in a visual search task, selectively for the most difficult target detection trials. The typical relationship between prestimulus alpha power over posterior cortical areas and reaction time (RT) to targets during tSMS is altered such that tSMS-dependent increases in alpha power are associated with longer RTs for difficult, but not easy, target detection trials. Our results directly demonstrate that a powerful magnet placed on the scalp modulates normal brain activity and induces behavioral changes in humans.

Letter to the editor: No influence of static magnetic stimulation applied for 30 minutes over the human M1 on corticospinal excitability

“…Such strategies include performing sample size calculations [7], using neuronavigation to ensure stable coil positioning [6], and refraining from pre-selecting or pooling participants on the basis of being responders or not to a given NIBS intervention [8]. Finally, as the relevance of MEP amplitude alterations in drawing inferences on cortical functioning remains poorly understood [9], the failure of tSMS to alter CSE does not necessarily entail that tSMS has no influence on cortical functioning [10]. Nonetheless, the neurophysiological effects of tSMS should be clarified and confirmed before considering a widespread implementation of the technique.…”

Combination of Static Magnetic Fields and Peripheral Nerve Stimulation Can Alter Focal Cortical Excitability

“…The effect of tSMS was also showed to reduce cortical excitability both in the sensorimotor cortex of humans (Oliviero et al, 2011; Silbert et al, 2013; Kirimoto et al, 2014; Nojima et al, 2015), and in the visual cortex of cats and monkeys (Aguila et al, 2016). Furthermore, the significant behavioral changes were recently reported with the application of tSMS to the visual cortex in monkeys and humans (Gonzalez-Rosa et al, 2015; Aguila et al, 2016). …”

The many characters of visual alpha oscillations

“…For example, during spontaneous periods of low alpha power, people are more likely to report seeing visual phosphenes during transcranial magnetic stimulation of visual cortex (Romei et al ., ) and to perceive visual stimuli when none has been presented (Iemi et al ., ). Furthermore, supporting the negative association between alpha power and visual excitability, static magnetic field stimulation of visual cortex, which is thought to inhibit neural activity (Oliviero et al ., ), induces significant increases in alpha power (Gonzalez‐Rosa et al ., ).…”