Aftereffects of alpha transcranial alternating current stimulation over the primary sensorimotor cortex on cortical processing of pain

Abstract

Transcranial alternating current stimulation (tACS) is believed to modulate brain oscillations in a frequency-specific manner. Given the correlation between sensorimotor a-oscillations and pain perception, tACS that targets sensorimotor a-oscillations has the potential to reduce pain. Therefore, this study sought to determine the aftereffects of a-tACS over unilateral primary sensorimotor cortex (SM1) on the perceptual and neural responses to noxious painful stimulation of the contralateral hand. Using a double-blinded and sham-controlled design, 60 healthy participants were recruited to receive either a-tACS or sham stimulation of unilateral SM1 through an electrode montage in a 4 3 1 ring configuration. Neural responses to laser nociceptive stimuli were assessed using functional magnetic resonance imaging immediately before and after a-tACS intervention. Perceptual reports were recorded simultaneously. Compared with sham stimulation, a-tACS attenuated bilateral SM1 responses to painful stimuli delivered to the contralateral hand. Although a-tACS did not exert direct effect on subjective pain perception, it can indirectly decrease ratings of pain perception by reducing brain activity within the targeted SM1. Moreover, a-tACS decreased the functional connectivity between the targeted SM1 and a network of regions that are crucially involved in pain processing, including the middle cingulate cortex, contralateral somatosensory cortex, and dorsolateral prefrontal cortex. These results demonstrated that after a-tACS applied over the unilateral SM1 does attenuate subsequent neural processing of pain within bilateral sensorimotor regions as well as sensorimotor functional connectivity. The findings provide evidence that sensorimotor a-oscillations directly affect pain processing and support the application of sensorimotor a-tACS for inducing pain analgesia.