Transcranial Direct Current
Stimulation (tDCS) is a type of neurostimulation where you apply a very small level of
direct current through one electrode (Anode) and it flows through the brain to
another electrode (Cathode).
This has a pronounced physiological
reaction. The direct current creates a condition under the electrode that
affects the neurons: the basement membrane of the neurons at the anode become
more positive making them more likely to fire, and the basement membrane of the
neurons at the cathode become more negative making them less likely to fire.
Through this simple method, tDCS has
been researched to increase insight, improve learning of new things, and also
help treat depression and stroke.
For the cognitive enhancement, it is
necessary to be performing the task you want to learn while you are stimulating
(or inhibiting) with a TDCS device the areas that will be neurologically active
during the learned activity. This way the neurons are more likely to fire, and
hence increasing brain plasticity.
But what is happening
electrically?
(For a more detailed discussion on the Electrical Nature of tDCS go to the blog)
The exact pathways of current from
the anode electrode to the cathode electrode through the brain is not entirely
known. The modeled circuit of the head (including skin, periosteum, skull,
brain..) can be considered a simple design of just a resistor. But in reality
that is not the case at all with so many non uniform materials the current must
flow through.
It is more likely a much more complex
system with some current flowing along the connective tissue in the scalp, and some
flowing through the brain. It is generally known that the current intensities
are highest under the anode and cathode electrodes; but from a bigger picture of
current density to increased positive charges at the basement membrane is a
large step (is it capacitive from the skull, with charge buildup on both
sides?) I imagine we will soon know more.
