Effects of multifocal transcranial direct current stimulation targeting the motor network during prolonged experimental pain

Abstract

Background Antinociceptive effects of transcranial direct current stimulation (tDCS) over the primary motor cortex (M1) have been extensively studied in the past years. However, M1 does not work in isolation, but it rather interacts within a network, the so‐called resting‐state motor network. Objective To explore the anti‐nociceptive effects of a new multifocal tDCS approach administered to regions linked to the resting state motor network (network‐tDCS) compared to sham tDCS. Methods Healthy individuals were included in this randomized, parallel and double‐blinded study comprising two consecutive interventions with 24‐hr interval of either active (n = 19) or sham (n = 19) network‐tDCS. Prolonged pain was induced by application of topical capsaicin on the dorsum of the hand during a 24‐hr period. Assessments of corticomotor excitability (transcranial magnetic stimulation), pain ratings (numerical rating scale, NRS), skin pain sensitivity on the arm (heat and mechanical), temporal summation of pain (TSP) and conditioned pain modulation (CPM) were performed at baseline (Day1‐baseline), after 25 min of capsaicin application and before the first tDCS session (Day1‐post‐cap), and after the second tDCS session (Day2). Results Comparing Day2 to Day1‐baseline measures, there was reduced corticomotor excitability (p < .05) and impaired CPM‐effect (p < .05) after sham but not after active network‐tDCS. Pain NRS ratings increased at Day2 compared to Day1‐post‐cap (p < .01) in both groups whereas no significant changes were found in pain sensitivity and TSP. Conclusions Present findings demonstrate that tDCS applied over regions linked to the resting state motor network reverts the inhibition of corticomotor excitability and CPM impairment both provoked by prolonged experimental pain for 24 hr. Significance These findings highlight that the stimulation of the resting state motor network with multifocal tDCS may represent a potential cortical target to treat chronic pain, particularly in patients exhibiting maladaptive corticomotor excitability and impaired conditioned pain modulation effects.

Multitarget high-definition transcranial direct current stimulation improves response inhibition more than single-target high-definition transcranial direct current stimulation in healthy participants

“…The results seemed contradictory because of the assumption that electric field intensity in a brain area directly associates with the behavioral effect of tDCS (Evans et al, 2020). One highly possible explanation may lie in that efficient execution of brain function is based on networks of brain areas rather than individual brain regions (Hoogman et al, 2017;Ester and Kullmann, 2021); and multitarget stimulation tries to modulate the associated brain network and may result in additive effects of tDCS on performance compared with singletarget stimulation (Brem et al, 2018;Ester and Kullmann, 2021;Friehs et al, 2021a;Gregoret et al, 2021). Additionally, there is some evidence for the potentially inverted U-shaped nature of tDCS interactions with behavior performance, in which an intensity may lead to better performance when it lies closer to the peak of the inverted-U curve (Ehrhardt et al, 2021).…”

“…It is well known that the normally effective execution of brain function is based on neural networks rather than on isolated brain regions (Ester and Kullmann, 2021). Simultaneous HD-tDCS with identical polarity on multiple functionally related brain regions -in other words, multitarget stimulation -can regulate cortical excitability more efficiently and enhance tDCS effects more prominently than singletarget stimulation (Fischer et al, 2017;Hill et al, 2018; 10.3389/fnins.2022.905247 Ester and Kullmann, 2021;Gregoret et al, 2021). Multitarget HD-tDCS has been applied to studies of motor ability and working memory and the results have demonstrated that multitarget stimulation is more effective (Dagan et al, 2018;Hill et al, 2018).…”

During capsaicin‐induced central sensitization, brush allodynia is associated with baseline warmth sensitivity, whereas mechanical hyperalgesia is associated with painful mechanical sensibility, anxiety and somatization

“…Specifically, state anxiety enhances attentional capture of painful stimuli and brief cognitive behavioural interventions have been shown to decrease the area of secondary hyperalgesia after capsaicin exposure. Furthermore, noninvasive brain stimulation of the cortex in healthy subjects ameliorates capsaicin-driven secondary hyperalgesia (Gregoret et al, 2021;Hughes et al, 2020;Meeker et al, 2019;Seifert et al, 2010). Also of note, there was no correlation between PCS and mechanical hyperalgesic magnitude.…”

The Concept, Development, and Application of a Home-Based High-Definition tDCS for Bilateral Motor Cortex Modulation in Migraine and Pain

“…For instance, bilateral anodal tDCS over the tongue M1 in healthy individuals induced more enhanced cortical excitability and tongue motor function than unilateral stimulation ( 84 ). Also, in a later study with healthy individuals, multifocal tDCS with bilateral M1 as anodes reverted an inhibited corticomotor excitability and impaired conditioned pain modulation that had been induced by topical experimental pain ( 85 ).…”