Full transcript: [intro music] Host – Dan Keller Hello, and welcome to Episode Eighty-eight of Multiple Sclerosis Discovery, the podcast of the MS Discovery Forum. I’m Dan Keller. You may have heard of transcranial magnetic stimulation, a treatment for migraine, neuropathic pain, and treatment-resistant depression using an electromagnet positioned on the scalp. Dr. John Hart, a professor of neurology and neurotherapeutics at the University of Texas Southwestern Medical Center in Dallas, is now testing another electrical technique called transcranial direct current stimulation, or tDCS, as well as alternating current to improve cognition in brain disorders, potentially including MS. An even more directed form, called high definition tDCS, allows more precise targeting of brain areas. The experimental procedure involves placing electrodes strategically on the outside of the head. We spoke in his office about how he's going about developing the technique and how it may eventually be combined with other therapeutic modalities. Interviewer – Dan Keller You're working in transcranial direct current stimulation. Basically, what is it; how does it work or be applied? Interviewee – John Hart tDCS is short for that. You'll have an electrode – actually it's a sort of small doughnut, so it's not such electrodes that people think of tiny little electrodes – and you place one on one part of the scalp area, and then another part, and you're basically going to pass current through the head in a sort of diffuse, generalized way, not very specific, from that one electrode to the other. Recently, a new sort of area has been developed, a new cap system approach called high definition transcranial direct current stimulation. It's an EEG cap with EEG electrodes on them, and you can pass current out one electrode and draw it in a variety of other electrodes. So you can target it to specific areas where it's coming out, and you can also direct it as to where it goes through to multiple, depending on how specific or not, brain regions that you're going to have the electrode come out. So if you want to hit one spot, you can go out one and bring it in its surrounders and keep all the current there, or you can go from one place to another. And in some instances, we're able to throw it – sort of like throwing your voice – down the deep structures and sort of hit those as a way of stimulating. The other part about it is the direct current part. We also do alternating currents, or HD TACS, and we can do frequencies and other things, too. So I feel that this has got a fair amount of promise and flexibility as a way to externally stimulate brain areas pretty safely. It does a little tingling to your scalp kind of side effects in terms of application. MSDF What kind of currents and voltages does it involve? Dr. Hart Right now normally in tDCS in the big things, we do 2 milliamps ballpark. We find that 1 milliamp is about where we're functioning now at the high definition, and right now we're doing studies with it where we're playing around with the amps and different frequencies to see – since it's relatively a new technique – what sort of effects you get. So … it's so new there's not a ton of papers out about it for me to tell you where we're going to land, will there be a dose-response curve? We're doing those studies right now.   MSDF You've said that you’re interested, in general, in cognition across all sorts of brain disorders—Alzheimer's, MS, others. What's the hypothesis for using this kind of stimulation? Dr. Hart Well, in my primary research area I do word retrieval and knowledge retrieval and storage, so we've mapped out in that example a circuit of the pre-SMA, the pre-supplementary motor area, and the caudate and the thalamus that's involved in retrieving a memory. So when I say desert a