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Transcranial Direct Current Stimulation (tDCS)

Publication date: 22 February 2012

Recently New Scientist magazine published an article on Transcranial Direct Current Stimulation (tDCS) reflecting a growing level of interest in the subject. Current research is exploring the therapeutic efficacy of tDCS, but as the article indicates, also its potential in helping all of us access optimal performance, especially in learning. Whilst tDCS must still be regarded as an experimental therapy it clearly has lots of potential, and tDCS and other forms of neurotherapy and neurofeedback are available to clients of York Mind-Body Health.

What exactly is tDCS? It's a very simple form of brain stimulation – indeed it's hard to imagine a much simpler technology. The hardware is little more than a 9V battery together with a means of connecting its positive and negative terminals to the head. One of the poles is applied to a relatively small area of scalp using a salt water soaked sponge to carry the voltage. The other pole is attached to a wider area, either somewhere else on the scalp or on the neck or shoulder. When the device is turned on, a constant voltage is applied, creating a tingling sensation, and a total current of something like 1 milli-amp. A typical session lasts about 20 minutes, and the research suggests repeated sessions numbering of the order of 10 to be efficacious.

There are a couple of choices to make. Firstly, where to place the electrodes, or in effect which part of the brain to stimulate, and secondly whether to apply positive (or anodal) stimulation or negative (cathodal) stimulation. The former is thought to enhance neuronal excitability, while the latter inhibits it. Both are potentially therapeutic, and bear in mind that the brain's internal dynamics mean that stimulating one part of the brain is likely to inhibit other parts not being directly stimulated.

What does it mean to change neuronal excitability? It means making neurons either more or less likely to fire. That's also what neurotransmitters seem to do – and of course much of mainstream therapy for disorders such as anxiety and depression is pharmacotherapy targeted at neurotransmitters. Typically for anxiety you'd want to make neurons less excitable, on the assumption that they're actually over-active. (Incidentally at least one study suggests tDCS may alter dopamine dynamics.)

On what basis do we make these two choices of location and polarity? Because tDCS is an experimental technology there are no hard and fast rules. Speaking personally I take into account firstly the results of brain assessments, most notably a simple form of EEG assessment that I've described in previous blog posts. Secondly, my client's pattern of symptoms (e.g. depression, attention problems), and thirdly knowledge of brain functioning and research findings. An example of the latter is the discovery that emotional positivity correlates with a greater activation of the left prefrontal cortex relative to the right. Depressed people tend to have the opposite, so therefore an obvious protocol for tDCS is to positively stimulate the left side. This is what some of the researchers have tried (e.g. see this paper by Fregni et. al.) apparently with some success. Of course all depressed people may not show this asymmetry, which is why it is useful to do some form of brain assessment.

Research has shown tDCS may be effective for mood problems, cognitive problems such as working memory, chronic pain, stroke and brain injury, alcoholism and sensory perception. The effects seem to be long-lasting.

One of the most interesting ideas is around is that tDCS may enhance learning (e.g. see this tDCS article and tDCS research paper). Perhaps by affecting a type of brain cell structure called the NMDA receptor, which is associated with learning. Related to this is the idea that the New Scientist article explored, that tDCS may facilitate access to flow states.

I haven't come across any research that found safety issues with tDCS, although it is worth saying that the long term effects of repeated stimulation are unknown, and also that anything that is capable of positive effects may also have deleterious consequences if used in the wrong way.

Nonetheless I feel very excited for the future of this technology, not least because unlike many new treatments we hear about in the media, it is amazingly cheap. (I'm using tDCS equipment developed by Mind Alive, Canada.) I look forward to working with more clients using tDCS.

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