What's the deal with Anode and Cathode in tDCS?
tDCS always has an anode electrode and a cathode electrode, so what?
Well, one of the first things you learn about Transcranial Direct Current Stimulation (tDCS) is that you put the anode electrode over the part of the brain you wish to excite and the cathode electrode over the part of the brain you wish to inhibit. This idea seems as old as the original modern tDCS paper by German scientists Dr. Nitsche and Dr. Paulus. But newer papers from these same labs seems to suggest it's not that simple after all. For example, increasing the current at the cathode can make it excitatory while increasing duration at the anode can make it inhibitory. Plus—it’s really unclear if when you’re dealing with more complicated brain functions like learning a language or playing a video game, if the brain can really just be thought as simply acting like a knob that you wind up and down. It’s important to realize that you always have to have both the anode electrode and the cathode electrode on together—if you put just one electrode on the head, tDCS won’t work at all, behaving in the same way as needing to complete a circuit to actually light a light bulb.
So, what could you do if you only wanted the effect of one electrode, but not the other? For example, you may want the anode to boost a specific area or function of your brain, but may not want to deal with the other electrode—say you don't want any possible cathodal inhibition.
One approach is to assume both electrodes act as effective brain boosters—which could be the idea behind the Halo TDCS device since you’d want to boost both sides of your body.
Another approach is to stick to proven montages that have already been shown to work for whatever brain function it is you wish to boost. Check out our montage guide.
If you got the resources, High-Definition tDCS lets you pick and choose just anode or cathode.
Finally, you can leverage the fact that you indeed have anodal and cathodal influences, and try an approach where you boost one area and inhibit another area at the same time, which researchers have tried.