transcranial direct current stimulation

[eub]

http://www.nature.com/news/2004/041025/pf/041025-9_pf.html

Connecting a battery across the front of the head can boost verbal skills, says a team from the US National Institutes of Health.

A current of two thousandths of an ampere (a fraction of that needed to power a digital watch) applied for 20 minutes is enough to produce a significant improvement, according to data presented this week at the annual meeting of the Society for Neuroscience, held in San Diego. And apart from an itchy sensation around the scalp electrode, subjects in the trials reported no side-effects.
[...]
The volunteers were asked to name as many words as possible beginning with a particular letter. Given around 90 seconds, most people get around 20 words. But when Iyer administered the current, her volunteers were able to name around 20% more words than controls, who had the electrodes attached but no current delivered. A smaller current of one thousandth of an amp had no effect.

This sounds simpler to implement than transcranial magnetic stimulation. In fact, at work we have several Keithley SMUs that could be set to source 1000 μA, 2000 μA, whatever you like. (YES YES I know several reasons why this is a rotten idea. Even if I turn off the damned broken autoranging mode.)

Transcranial Direct Current Stimulation during Sleep Improves Declarative Memory.

Pharmacological approach to the mechanisms of transcranial DC-stimulation-induced after-effects of human motor cortex excitability.

Excitability changes induced in the human motor cortex by weak transcranial direct current stimulation.

Comments

[hattifattener]

Huh. This is interesting: from your last two links, which seem to have the most info:

Increase of cortical excitability could be selected by anodal stimulation, and decrease by cathodal stimulation.

and

In general, cerebral excitability was diminished by cathodal stimulation, which hyperpolarises neurones. Anodal stimulation caused neuronal depolarisation, leading to an increase in excitability [....] However, in single cortical layers opposite effects were seen [...] underlining the fact that the effects of DC stimulation depend on the interaction of electric flow direction and neuronal geometry.

[eub.livejournal.com]

Yeah, it's interesting that it's not an effect of the electric field itself. I forget my electrochemistry -- the effects near an electrode would be ion traffic, maybe? (I'm actually pretty surprised that the skull doesn't act as a good insulator, channeling current through the scalp.)

With the anodal/cathodal business, my reading of the Nature article was that if they'd swapped the leads, it might have depressed verbal skills instead.

In general accordance with basic neurophysiology, anodal stimulation of the motor cortex enhanced excitability, whilst it was diminished by cathodal stimulation. The reason for this is most probably that anodal stimulation - as so far shown in animals - results in neuronal depolarisation and increasing neuronal excitability while cathodal stimulation has opposite results.

Oh, you and your "basic neurophysiology". Let's see. Anode is positive. Exterior of neuron is positive vs. interior. Anode raises exterior more positive? That would hyperpolarize, depressing excitability, I should think. Anode raises interior potential?

The problem here is I have no idea why it would preferentially raise one vs. the other. I guess it would like to raise the better conductor more. Is that the interior?