Effects of transcranial direct current stimulation on pain, mood and serum endorphin level in the treatment of fibromyalgia: A double blinded, randomized clinical trial

Frequency‐dependent top‐down modulation of temporal summation by anodal transcranial direct‐current stimulation of the primary motor cortex in healthy adults

“…These lines of evidence have now not only shown a reduction in pain intensity in chronic pain patients, but also distinct changes in the brain regions involved in the top‐down modulation of pain processing. In a recent study, tDCS improved clinical pain and mood ratings in fibromyalgia patients which was correlated with changes in serum endorphin levels (Khedr et al., ). This suggests activation of the opioid system, in part, mediates the analgesic effects of primary motor cortex tDCS and others have shown the release of opioids in the midbrain in both healthy subjects (Dossantos et al., ) and during chronic pain (Dossantos et al., ).…”

“…The results from human mechanistic studies in healthy volunteers have been more contradictory, with a number of authors reporting either weak or nonexistent analgesic effects (Boggio et al., ; Csifcsak et al., ; Hansen et al., ; Jurgens et al., ; Aslaksen et al., ; Ihle et al., ). This could be because tDCS is often delivered over a number of days in chronic pain patients which may result in an accumulation of top‐down analgesia (Khedr et al., ). Additionally, it could be due to the variability in the tDCS montages used in healthy subject studies.…”

“…They may also provide insight into the efficacy of tDCS in both clinical and nonclinical settings. There is a growing body of evidence that suggests tDCS is more effective in patients with chronic pain Borckardt et al, 2011Borckardt et al, , 2017Jurgens et al, 2012;Kim et al, 2013;Hagenacker et al, 2014;Bolognini et al, 2015;Volz et al, 2016;Ahn et al, 2017;Harvey et al, 2017;Khedr et al, 2017a) compared to studies that have attempted to dissect the analgesic mechanisms in healthy subjects (Boggio et al, 2008;Csifcsak et al, 2009;Hansen et al, 2011;Jurgens et al, 2012;Aslaksen et al, 2014;Ihle et al, 2014). These lines of evidence have now not only shown a reduction in pain intensity in chronic pain patients, but also distinct changes in the brain regions involved in the top-down modulation of pain processing.…”

“…Transcranial direct-current stimulation (tDCS) can modulate cortical activity by depolarizing or hyperpolarizing cortical neuronal resting membrane potentials depending on the polarity of current stimulation (Purpura and McMurtry, 1965;Gorman, 1966). There is a growing body of evidence that anodal tDCS applied over the primary motor cortex provides pain relief in a number of neuropathic, visceral and inflammatory chronic pain conditions (Borckardt et al, 2011(Borckardt et al, , 2017Jurgens et al, 2012;Kim et al, 2013;Hagenacker et al, 2014;Bolognini et al, 2015;Volz et al, 2016;Ahn et al, 2017;Harvey et al, 2017;Khedr et al, 2017a). However, the analgesic mechanisms mediating these effects have been more difficult to elucidate.…”

Neurophysiological basis of a new electrode configuration to potentiate the tDCS: Protocols for upper limbs

“…Interestingly, some of these changes in neuronal behavior are correlated with improvement of clinical symptoms in sensorimotor, emotional, and cognitive disorders [3][4][5][6] . On the other hand, a substantial portion of individuals are refractory and/or resistant to tDCS 3,7 .…”