The application of novel brain stimulation techniques to treat depression, and possibly other neuropsychiatric disorders, is a new and rapidly growing field. Among these techniques, transcranial direct current stimulation (tDCS) is emerging as one of the most promising approaches because of its relative ease of use, safety and neurobiological effects. tDCS involves the use of weak electric currents (1–2 mA), passed through brain tissue via electrodes placed on the scalp. The stimulation is too weak to directly cause neuronal firing, but is thought to interact with the neuronal membrane and background neural activity, resulting in modification of synaptic strength.
One of the most promising therapeutic applications of tDCS has been in the treatment of depression. A recent meta-analysis suggested that tDCS may have robust and clinically meaningful effects in treating depression. Active stimulation was more effective than sham stimulation, and 48% of subjects who received 30 treatments of tDCS (given every weekday over a period of 6 weeks) responded to treatment.
In the course of conducting this trial, it has been observed that tDCS may induce additional benefits that appeared to be independent of mood improvement. Several subjects spontaneously reported improved attention and concentration during the weeks when they were receiving active stimulation (given under double-blind conditions). One subject found that tDCS relieved her from neuropathic pain to the same extent as spinal block anesthesia,
These observations are consistent with reports in the literature of cognitive enhancement and pain relief with tDCS.
The use of tDCS to treat pain syndromes is another area of research that has attracted much interest, Therapeutic effects in pain syndromes have been shown with stimulation of motor and frontal areas.
From an understanding of the physics of tDCS, it is conceivable that stimulation administered primarily to frontal brain areas to treat depression may also have other clinical effects, as the stimulation is relatively diffuse. In recent depression trials conducted since 2000, tDCS was administered between widely spaced electrodes as this approach increases the amount of current entering the cranium (as opposed to being shunted over the scalp).
tDCS is a rediscovery of an old technology, and many studies are now exploring its therapeutic potential in a range of disorders. The therapeutic effects of a treatment are often weighed against side effects in a cost–benefit analysis. A treatment that has beneficial ‘side effects’ would be welcome indeed. It may even be possible that future stimulation paradigms are designed to utilize the diffuse nature of the stimulation to treat more than one set of symptoms at a time, for example, improving cognition while lifting mood in depression.