Pain Treatment by tDCS of the Human Primary Motor Cortex
Authors: Niels Hansen
Abstract: Chronic pain is an intractable clinical condition often resistant to therapeutic pharmacologic approaches. Alternative therapeutic strategies are therefore needed, i.e., non-invasive brain stimulation such as transcranial direct current stimulation (tDCS). tDCS of the human primary motor cortex (M1) is easy to perform and an inexpensive method to achieve pain reduction in patients and healthy subjects. Depending on the polarity, tDCS of M1 induces either an increase (anodal tDCS) or a drop (cathodal tDCS) in motor cortex excitability. This article addresses the antinociceptive effect of tDCS over M1 (M1-tDCS) and its underlying mechanisms. Pain relief after tDCS has been demonstrated in various clinical and experimental pain trials with tDCS. Anodal tDCS is efficient in chronic pain states comprising chronic pelvic pain, fibromyalgia, neuropathic pain in multiple sclerosis, post-stroke pain, spinal cord injury and trigeminal neuralgia.
Possible underlying mechanisms of beneficial M1-tDCS are modulation of neuronal activity in pain-related structures as a network-driven effect including structures such as the anterior gyrus cinguli, insula cortex, somatosensory cortex and thalamic nuclei, normalization of defective inhibitory mechanisms in chronic pain, and the changes in M1-reorganization often associated with chronic pain conditions. In conclusion, tDCS over M1 is a simple method to reduce pain in diverse clinical conditions.