Effects of transcranial direct current stimulation on pain perception and working memory

Abstract

Previous studies have shown that non-invasive stimulation of the dorsolateral prefrontal cortex (DLPFC) could modulate experimentally induced pain and working memory (WM) in healthy subjects. However, the two aspects have never been assessed concomitantly. The present study was set up to investigate the effects of transcranial direct current stimulation (tDCS) of the DLPFC on thermal pain and WM in the same population of healthy volunteers. In a randomized and balanced order of different sessions separated by 1 week, 20 min of 2 mA anodal, cathodal or sham tDCS were applied to the left or right DLPFC in two separate experiments. Twelve healthy volunteers were enrolled for each stimulated hemisphere. Warm and cold detection thresholds, heat and cold pain thresholds as well as heat pain tolerance thresholds were measured before, during and following tDCS. WM was assessed by a 2-back task applied once during cortical stimulation. Anodal tDCS of the right DLPFC led to an increase of tolerance to heat pain. The 2-back task revealed fewer outliers during cathodal tDCS of the left DLPFC. The present data show an involvement of the DLPFC in the processing of pain and WM. There was no correlation between these findings, suggesting that the analgesic effects of cortical stimulation are not associated with cognitive processing. However, this conclusion is difficult to affirm because of some limitations of the study regarding the parameters of stimulation or a ceiling effect of the 2-back task for instance.

Effects of transcranial direct current stimulation on the working memory of post-stroke people: an integrative review

“…They showed different interventions, which differed in the number of sessions and study design, thus making difficult compare them. Other variables, such as intensity of current, stimulated area, stimulation time and methods used to measure the outcomes were similar, corroborating with protocols used by other authors in different populations that investigated the same outcomes (19,20) . It is known that after stroke may occur a change in synaptic homeostasis, which affects individuals' cognition (21) .…”

Working memory improvement with non-invasive brain stimulation of the dorsolateral prefrontal cortex: A systematic review and meta-analysis

“…We also found that the Egger's test was not significant. Further, the funnel plot revealed that all studies were inside the boundaries of the funnel and symmetrically distributed (Supplementary Figure 3) and no particular study substantially changed the net result according to sensitivity analysis, which ranged from 0.234 to 0.276 after excluding experiments of Boggio et al (2006) and Mylius et al (2012). (Figure 2) …”

“…Two studies reported that a minority of their participants did not complete the study and withdrew because of side effects such as treatment intolerance (Barr et al, 2013) and headache (Mylius et al, 2012). Data of these participants were not analyzed.…”

“…Psychiatric patients were screened using standard questionnaires and/or psychiatric interviews. Only some studies reported that healthy volunteers were not on medication that could affect the central nervous system (Keeser et al, 2013;Mylius et al, 2012), but these subjects were, in most studies, screened to exclude a psychiatric diagnosis (Esslinger et al, 2012;GaudeauBosma et al, 2012;Keeser et al, 2013;Teo et al, 2011). Importantly, tDCS studies enrolled more healthy volunteers and rTMS, more neuropsychiatric patients.…”

“…Finally, sensitivity analysis showed that no study significantly influenced the results, with the net effect size varying from -0.21 to -0.24 when the experiments of the study of Mylius et al (2012)were respectively excluded. (Figure 1 (Figure 2).…”