Static Magnetic Field Stimulation over Parietal Cortex Enhances Somatosensory Detection in Humans

Abstract

The role of neuronal oscillations in human somatosensory perception is currently unclear. To address this, here we use noninvasive brain stimulation to artificially modulate cortical network dynamics in the context of neurophysiological and behavioral recordings. We demonstrate that transcranial static magnetic field stimulation (tSMS) over the somatosensory parietal cortex increases oscillatory power specifically in the alpha range, without significantly affecting bottom-up thalamocortical inputs indexed by the early cortical component of somatosensory evoked potentials. Critically, we next show that parietal tSMS enhances the detection of near-threshold somatosensory stimuli. Interestingly, this behavioral improvement reflects a decrease of habituation to somatosensation. Our data therefore provide causal evidence that somatosensory perception depends on parietal alpha activity. Artificially increasing alpha power by placing a powerful magnetic field over the somatosensory cortex overcomes the natural decline in detection probability of a repeated near-threshold sensory stimulus.

Static magnetic field stimulation applied over the cervical spinal cord can decrease corticospinal excitability in finger muscle

“…The effects of the static magnetic field intervention on behavioral indices have been confirmed in animal studies ( Saunders, 2005 ). Even in humans, the static magnetic field stimulation can alter sensory function ( Gonzalez-Rosa et al, 2015 , Carrasco-Lopez et al, 2017 ). Thus, it is possible that tsSMS can also modify human motor or sensory function.…”

“…However, since static magnetic field stimulation induces only suppression of the motor system ( Oliviero et al, 2011 , Nojima et al, 2015 ), tSMS might not be useful for able-bodied people who want to improve motor behaviors, such as building muscle strength. A recent study reported that tSMS over the parietal cortex facilitated somatosensory detection ( Carrasco-Lopez et al, 2017 ). Thus, tSMS may be able to facilitate systems other than the motor system in both patients and able-bodied people.…”

“…For instance, Gonzalez-Rosa et al (2015) demonstrated that tSMS applied to the visual cortex impaired the performance of subjects in a visual searching task. Conversely, Carrasco-Lopez et al (2017) showed that tSMS over the parietal cortex improved the detection of somatosensory stimuli. These two studies suggested that tSMS can alter not only cortical excitability, but also human behavior.…”

Moment-to-moment fluctuations in neuronal excitability bias subjective perception rather than decision-making

“…This is potentially problematic, because it is known that both detection rate and excitability change over the course of an experiment. Specifically, behavioral measures such as hit rate (Boncompte et al, 2016;Carrasco-López et al, 2017) and sensitivity (Maniscalco et al, 2017) tend to decrease over time, possibly due to progressive fatigue, resulting from an exhaustion of cognitive resources. Likewise, ongoing α-power tends to increase over the course of an experiment (van Dijk et al, 2008), suggesting a decrease in excitability, possibly as a result of fatigue (Kaida et al, 2006).…”

Accuracy in Pinch Force Control Can Be Altered by Static Magnetic Field Stimulation Over the Primary Motor Cortex

“…tSMS over the visual cortex also reduces the discomfort induced by high‐intensity light stimuli . Furthermore, tSMS over the parietal cortex has been found to enhance the detection of somatosensory stimuli . These findings suggest that the effect of tSMS might be strong enough to modulate human behavior, and may therefore have clinical applications.…”