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.
What kind of currents and voltages does it involve?
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.
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?
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 and humps, does that make you think of a specific object? When camel pops into your head, we mapped out with fMRI, EEG depth, and electrodes this sort of electrical pattern of that retrieval circuit to effectively pull up that memory. So the way we've been doing it, we came up with this circuit in normal people, and we've seen certain disease states where it's dysfunctional, and MS happens to be one of them. So we're directing, right now, our current to the pre-SMA and trying to stimulate that circuit to hopefully have a less functional circuit become more functional, where it can pull out the signal to noise and fire off the right rhythms or get their rhythms in a correct pattern that are not there.
Psychiatry's done a lot better in terms of treatments, because a lot of the disorders are based on neurotransmitters and neurotransmitter states, that a drug will affect those neurotransmitters, and it hits all the areas, because it's more the transmitter than the place. Cognition has a lot to do with place and connectivity. Drugs, we've not got a ton of them as the primary cognitive treatment because they don't go to a specific place, and they don't effectively change that specific area's connectivity and/or its links.
I have a big study we just finished with RTMS [repetitive transcranial magnet stimulation] in PTSD [posttraumatic stress disorder]. I look at the fact that having worked as an electrician of cognition for years, that that's what the circuit is, and the best way for me to change cognitive status in the way that it's lined up its focal networks is probably not showering a brain with drug that won’t go to specific areas but maybe targeting things like electrical and magnetic current.
In terms of MS or other diseases, have you done any clinical studies so far?
So we're right in the middle of doing some MS patients preliminarily. And I don't get excited easily – I'm normally a pessimist, I think, at heart for these things. We've had some encouraging results in having people not on meds or who have failed meds or not had a response to meds that we've looked at retrieving memory in both word retrieval and in episodic memory retrieval and seen some improvements that have been relatively reasonably long-lasting from my point of view, lasting over months. But we've only at this point done about 5 or 6 people and we're enrolling more folks. We had a grant proposal in and we needed to get more folks to do a bigger trial. We're doing some placebo and then add people later to also see how much of this is a fair sort of setup as a placebo effect versus not. So we're advancing getting more and more folks into those stages now. And we've tried a few folks with TBI [traumatic brain injury].
How long do you apply the treatment. Is it a one-shot deal and what's the residual effect? You said you've had benefit up to months, is that from a series or from just once?
We're doing one-shot now as a way of figuring out dosing and effectiveness, since it's a relatively new device. The way we're doing the treatments for folks is to do 20-minute sessions and 10 of those over a 2-week period. So once a day, 20 minutes, for a total of 10 sessions. And that has seem to have been from animal studies and some other folks in the literature reasonable time and reasonable number of sessions at this point. We're going to figure out and look at more about adjusting dose, dose response, will we need boosters if it starts fading, and things like that. Its affect fades, because in essence these folks are not treated with modafinil or stimulants that we're doing this, so we're not doing it in conjunction with that. So they're not receiving what are typical cognitive treating medications in MS. So that's a plus side, and that we haven't had any serious any sort of residual side effect things at this point.
So if it lasted several months and you had to reapply a booster thing, compared to taking amphetamines or some of the other pro-amphetamine drugs, I think the upside is reasonable enough to say that compared to that, it would be a reasonable issue if you came in 4 times a year if that's what we need to do. But we'll see as we keep following folks.
If it works as you said, kind of separates out the signal from noise, essentially boosts the signal, the signal is gone when you turn it off or when someone leaves the treatment room. So what do you think, something's happening biochemically, or what's it doing that gives you a long-lasting effect?
When we just finish our RTMS trial for post-traumatic stress disorder, one of our interesting findings was the length of time, or the time when the effect lasts, or how long it lasts and continues. So there are some studies on electrical stimulation in animal models that suggests that what it does is set up a state called meta-plasticity. And the meta-plasticity in the animal models support the fact that long-term potentiation and synaptic potentials that can be set up down the road are actually benefited from the electrical stimulation. And that's what's encouraged us a little bit looking at stuff to see why these things last, because the first thing always like a single-shot, it fades off, it fades away.
Luckily, for some of this stuff we have some guidance from animal models. And this meta-plasticity phenomena has been noted for a continue – or delayed almost – effect of when you see improvement because of this. I think it's a state potential change that long-term potentiation can occur down the road. That's our best guess at this point.
You said besides direct current stimulation, you're also trying alternating current. With a direct current, you probably would not get anything analogous to a magnetic stimulation because you wouldn’t set up a magnetic field. Do you see differences between your direct current stimulation and your alternating current stimulation?
We sure have – and I must admit none of this has been published yet because we're trying to set parameters. Initially, the enthusiasm for alternate current stimulation waned a lot, I think, for folks for any of these things, because it didn't seem to be nearly as effective as direct current. And I think as a lot of this stuff initially was done in normals. And I'm not so sure that when you have patients with a disease state, depending on what the disease state is, that I'm willing to sort of say that alternating current is not necessarily going to be useful or not. Also, this is very directional, so here's anode and cathode. So you can take the same current, same electrodes, change the directionality and get different effects. And typically people that found those things in the motor system were pretty noticeable.
In cognitive systems, we haven't seen that as much, that when we flip the direction of the current, that we're getting the opposite effects—so instead of enhancing a performance in something, that we're knocking it out. So I think once we look at sort of these things, every new approach has to be taken really as a start from scratch, do the hard work of just what we're doing, change the amplitudes, change the parameters, change the direction in a nice, safe way in single shots, and which we've been doing, and then record pre- and post.
We do a lot of electophys measures, but also cognitive measures and other sorts of measures to see how each one of these effects things, and do we have something that I would hope one day I'll be writing electrical prescriptions. And I'll say you should get F4 to CZ current at 1 milliamp or 0.5 milliamps, or whatever I wind up doing, for 10 sessions, 20 minutes. Or, no, my god, look at this, we've got to go from here to here at a different milliamp. Once we start looking at that, I think to me also frequencies are very important; can I send different frequencies instead of milliamps. We're going to discover a lot of different things work differently, especially in diseases that are not a homogeneous thing.
Brain disease is not like liver cancer. Hepatocytes, it's like how many hepatocytes are not working and how big is the tumor? No, not having a good thalamus is very different than not having a functional motor cortex, you just see entirely different results. So I think it's going to be a lot more complicated, but I think doing it in a systematic way in normals, and then applying it to certain disease states gives us our best chance at coming up with primary or as adjunct treatments to other ways we're going to be treating diseases that have cognitive problems.
It doesn't seem surprising that the polarity wouldn't matter, because not all the neurons, dendrites, and synapses are lined up in one direction; they're going in all different directions, so even their polarity is different. It seems like zapping it in one direction for one, but the opposite direction for the other anyway.
We've actually done stuff with EEG measures and fMRI measures, and done these things called Granger causality models. So how much does, say, one time point predict an activation or a change in the other time point? And in an area that we thought was really this guy is telling that guy what to do, we found that most of those were predominantly a lot of two-way interactions that are constantly going on, and there's a lot of feedback between these systems.
And I always try to think like neurons and think electrically, and I can do it for about a couple hours and then my head starts really hurting. And in reality, I think the simplistic: Turn this light switch on and that you have a serial processing circuit is not really how electrically two neurons are always working together, or talking to each other, or keeping a tone or a level up. So I think you're right, I learn a lot every day. It's been sort of a cool job to figure out, yeah, that makes sense, because really it's an interactive set of neuronal firings.
Do you see any role for combining it with drugs that have ionotropic effects?
Yeah, I do. And the other part of that is going to be really, to me, which I think has been a problem with a lot of approaches to cognition and treating them, the timing of when and how you add different therapies together are going to be very, very important. Even now to say, all right, let's say I want to do a behavioral therapy with HD [high definition?] tDCS, well do you do it during it, do you do the HD tDCS continually? Do you pre-prep the brain by doing that first, and then doing cognitive rehabilitation strategies and therapies? I think we glibly just put things together without thinking that there might be an order to this. So right now we're looking at what's called state changes. We're not the first folks to do this, but some people say before you do tDCS, and that's before this HD stuff, you do a little RTMS first to set the state of the neurons in that area so they're more receptive to whatever you're going to do with the tDCS.
Just to be clear on it, RTMS is repetitive transcranial magnet stimulation.
So I think we're looking at kind of like, you know what, you get your pre-meds before you get your chemo so you don't vomit or do this or that. We might be finding ways that electrically how we're going to, or even you use meds prior to a treatment electrically, or vice versa, that that timing is going to be where the money is in terms of working out what are going to be the most effective therapies.
What have we missed? I realize it's still pretty early, but is there anything important to add?
I think the way we've done it is not going to always be available, in that we came from a circuit that we worked out, and we have an idea as to what we were trying to do. And we're measuring all these brain rhythms as outcome measures, so I know when I'm supposed to see alpha and beta rhythms to do that. And I think what's going to happen is we're not always going to have these circuits, we're going to have a spot. Like we've talked a little bit, shall we try to hit the hippocampus? And what other diseases would you do these things in? And the question's going to be when you're doing that, or doing that as a general approach, how do you smartly do it, when you really are not sure about the circuit?
We don't have a ton of really well worked out cognitive circuits in an active state of doing things. We have a lot of functional connectivity rest states, and you say I'd like to amp up that connectivity. I don't know what that does functionally, if you electrically take a rest state that normally is when your eyes close and add current to it. So I think while we've targeted this in the two areas that we're using electrical therapy in, post-traumatic stress disorder and this, and the things we've chosen, we built it off of normal studies.
The things we've got to be careful about, thoughtful about, and open-minded to at the same time about, is what if we want to treat something different than this? We want to do working memory, we want to do episodic memory, we want to do frontal behavioral problems. And if we don't have a circuit, try our best to get the most reasonable pre/post measures. Do single shots just to see what it does in a transient state, and then sort of work our way through the fact that at least a reasonable pre/post model and start thinking of this not as one-size-fits-all, but may be 0.5 milliamps, maybe TACS, maybe pink noise, maybe whatever sort of way you want to deal with it. It's going to take a lot more thought, I think, than people might casually say, hey, got some electrodes?
I mean, what bugs me right now is you can set up your own tDCS device off the internet, one of them using a car battery – 2 pieces of metal and some wire. And I highly would tell all those out there, which I know none of your listeners, don't do that. So when people started sort of exploring around in what they're going to do, I hope as we take this field further that we need to do it in a systematized fashion and a thoughtful way, because there's a lot of information you can get when something doesn't work. So you know what, I didn't change a thing here when I did this.
Well, I would like to know that, you know, is somebody else trying to do it, and try to collect this information that might be useful to other people trying to do things. Saying, you know what, we did this electrodes, these are these things in normals or whatevers and didn't get a response, to try to come up with a way that we've got to take it for the fact that it's like a med. It's going to have schedules, it's going to have doses. So if you're taking it twice a day at 5 mg or 6 times a day at 40 mg, working all that out is going to clearly need to be done in a reasonable, thoughtful way.
I appreciate it, thanks.
Oh, thank you so much, I really appreciate your interest.
Thank you for listening to Episode Eighty-eight of Multiple Sclerosis Discovery. This podcast was produced by the MS Discovery Forum, MSDF, the premier source of independent news and information on MS research. MSDF’s executive editor is Carol Cruzan Morton. Msdiscovery.org is part of the nonprofit Accelerated Cure Project for Multiple Sclerosis. Robert McBurney is our President and CEO, and Hollie Schmidt is Vice President of Scientific Operations.
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For Multiple Sclerosis Discovery, I'm Dan Keller.