(231) Transcranial Direct Current Stimulation of the Prefrontal Cortex Modulates both Pain and Nociceptive Flexion Reflex (NFR) Activity

Abstract

Transcranial direct current stimulation (tDCS) is a form of noninvasive brain stimulation that can either enhance (via anodal stimulation) or depress (via cathodal stimulation) neural excitability in focal areas of the cortex through application of a low-intensity direct current. Although prior studies indicate that cortical application of tDCS is associated with modulation of experimental pain, the present study provides the first test of the simultaneous effect of tDCS on both pain ratings and modulation of nociceptive flexion reflex (NFR). Thirty-two healthy participants (15 female) completed three days of NFR testing, each separated by at least one week. On each testing day, participants received 15 minutes of either anodal, cathodal, or sham tDCS over the dorsolateral prefrontal cortex (order counterbalanced across participants). Active stimulation was delivered at 2mA. tDCS was immediately followed by 24 discrete noxious electrical stimuli delivered over the sural nerve, immediately posterior to the ankle, to elicit NFR. NFR was evoked concurrently with presentation of pleasant, unpleasant, or neutral images. Following each stimulation participants rated pain intensity using a 0-100 rating scale. Mixed linear modeling was used to analyze tDCS effects on pain and NFR magnitude while controlling for image content and within-session habituation. Results indicated that tDCS had a significant effect on both pain, F(2, 2169) = 4.37, p = .01, and NFR, F(2, 2169) = 36.39, p < .001. Pain was higher after cathodal versus sham stimulation, p < 0.001, d = 0.10, but did not differ in any other comparison. NFR magnitude was higher after cathodal versus anodal (p < 0.001, d = 0.43) and sham (p < 0.001, d = 0.48) stimulation. These findings indicate that tDCS stimulation affects both pain reports and spinal nociceptive modulation, and highlights the importance of the dorsolateral prefrontal cortex in descending inhibition of pain and nociception. Transcranial direct current stimulation (tDCS) is a form of noninvasive brain stimulation that can either enhance (via anodal stimulation) or depress (via cathodal stimulation) neural excitability in focal areas of the cortex through application of a low-intensity direct current. Although prior studies indicate that cortical application of tDCS is associated with modulation of experimental pain, the present study provides the first test of the simultaneous effect of tDCS on both pain ratings and modulation of nociceptive flexion reflex (NFR). Thirty-two healthy participants (15 female) completed three days of NFR testing, each separated by at least one week. On each testing day, participants received 15 minutes of either anodal, cathodal, or sham tDCS over the dorsolateral prefrontal cortex (order counterbalanced across participants). Active stimulation was delivered at 2mA. tDCS was immediately followed by 24 discrete noxious electrical stimuli delivered over the sural nerve, immediately posterior to the ankle, to elicit NFR. NFR was evoked concurrently with presentation of pleasant, unpleasant, or neutral images. Following each stimulation participants rated pain intensity using a 0-100 rating scale. Mixed linear modeling was used to analyze tDCS effects on pain and NFR magnitude while controlling for image content and within-session habituation. Results indicated that tDCS had a significant effect on both pain, F(2, 2169) = 4.37, p = .01, and NFR, F(2, 2169) = 36.39, p < .001. Pain was higher after cathodal versus sham stimulation, p < 0.001, d = 0.10, but did not differ in any other comparison. NFR magnitude was higher after cathodal versus anodal (p < 0.001, d = 0.43) and sham (p < 0.001, d = 0.48) stimulation. These findings indicate that tDCS stimulation affects both pain reports and spinal nociceptive modulation, and highlights the importance of the dorsolateral prefrontal cortex in descending inhibition of pain and nociception.