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    How Deep Brain Stimulation Works, as Explained by a Neurologist

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    Lex Berko

    Contributor

    Diagnosed with early onset Parkinson’s disease at the age of thirty-five, Andrew Johnson of Auckland, New Zealand chose to undergo a surgical treatment called deep brain stimulation (DBS) to keep his symptoms at bay. The video he released documents the drastic improvement in his quality of life since the surgery about four months ago. As he turns the DBS off, his whole body is immediately wracked with the trademark debilitating shakiness of his condition. When he turns it back on, his hand tremors dissipate, his voice stops quavering, and he is able to sit still.

    Many other people have documented the effects of DBS via YouTube and it’s easy to inadvertently spend an hour watching these glimpses of neuroscience improving people’s lives in real time. But what exactly is going on here? How does it all work?

    DBS is a FDA-approved surgical treatment for the movement disorders of Parkinson’s disease, essential tremor, and dystonia. Sometimes, with what’s called the humanitarian device exemption, it can also be used in severe cases of other neurological or psychiatric conditions where a patient is suffering tremendously and not responding to medication.

    Essentially, DBS is a brain pacemaker. Its job is to ameliorate the abnormal firing of neurons that underlies Parkinson’s, essential tremor, and so on. In preparation for surgery, a neurologist uses imaging technology to locate the problematic brain structure, which in the case of Parkinson’s is the subthalamic nucleus (STN). A dime-sized hole is then drilled into the skull and an electrode is affixed to the appropriate target in the brain. The electrode is then connected to a wire that is threaded under the skin down towards the chest where a programmable battery is implanted. Once the two connect, it is possible to normalize neurological activity by delivering electrical impulses directly to the brain.

    The whole setup can be controlled by the patient or doctor via a handheld remote. The remote can turn the DBS on and off, which is how you get the dramatic effects you see in Johnson’s clip.

    To find out more, I reached out to Barbara Kelly Changizi, MD, co-director of the Center for Neuromodulation at Mount Sinai Medical Center.

    MOTHERBOARD: With many medicines, you reach a point where you need more and more and more to feel the effects. Is there anything similar with DBS where you might need to have a higher amplitude or voltage for it to work?

    Barbara Kelly Changizi: It depends on the condition. For Parkinson’s disease, you might go up a little bit on the stim, but generally, you hold steady. Once it's implanted, certain conditions are held at bay for five years, eight years, even ten years. It’s not a cure for the disease, but it holds tremor, stiffness, and slowness really well for long periods of time with maybe only minor increase in amplitude.

    Essential tremor, once that worsens, that’s a little different. You might require higher amplitudes and that’s something that’s under investigation. There’s different questions of why that’s so. Is that because you become refractory? Do you become resistant to the DBS or is it because the disease is just so bad underneath that the DBS is still working really well, but it just reaches its limits? Or maybe we should have a different target?

    I have seen the some of the worst of the worst cases with essential tremor and sometimes, the tremor does break through and you have to go up on the amplitude.

    Is it possible for the body to reject the parts of the DBS setup, like your body could if you did body modification or had an organ donated?

    No, it’s very different. I’ve never seen it rejected. The big risks with implanting DBS that you worry about is getting a stroke because you are putting a big wire into somebody’s head. With an experienced surgeon, the risks are low. A risk of a major bleed is less than one percent, but it is there. The other thing would be an infection because now you’ve got this thing screwed down to your skull and you got a wire going into the brain.

    A pair of DBS leads entering the brain, via Hellerhoff/Wikipedia

    If that gets infected, like if people pick at their scabs at the site of the screw, it can track into the brain. It’s got a little train path in. Again, that’s extremely rare, though we screen for it. You make sure the wounds are well healed, but those are the two major complications more than something like rejecting the metal.

    I’m familiar with cranial electrotherapy stimulation for depression, anxiety, and chronic pain. To a layman like me, it sounded kind of similar in that it involves electrical activity to work with the brain on some level. Do they operate on any of the same principles? Are they similar at all?

    It depends on whether you’re stimulating superficially or deep. The whole principle with the deep brain stimulation is that you got a wire and it’s going into the brain. You’re not going outside the skull. I guess the idea of altering abnormal firing is similar. That idea is fine, but which targets you’re going for and how you’re going about it… one is with a fine tip electrode really targeting specific structures inside. It’s different.

    Could other sorts of electrical activity alter the activity of the DBS? The first thing that comes to my brain is an airport scanner. Is there anything else you wouldn’t necessarily think of, like cell phones or other medical devices?

    We counsel people on certain rules they have once they get the DBS. One is that you can get MRIs of the brain, but only under certain conditions. You can’t get an MRI from the neck down. DBS is a closed loop wire inside the head so you can actually induce current with the MRI magnet. The current then goes up and you can actually lesion the brain if you have inappropriate use of MRIs from the neck down. But you can do it under the brain under certain circumstances if precautions are done.

    General household appliances should be fine. The only thing I’ve seen is that certain things, either with magnets or high electrical fields, can sometimes turn the DBS off. I had one child who had DBS for a condition called dystonia and she had a Nook with a magnetic case. She had a battery on each side of her chest for each side of the brain. She was sleeping on the Nook and she was sleeping on one side. We couldn’t figure out why that DBS was always getting turned off every time she saw me in the office. And finally, we pieced together that she was holding the Nook against her chest and falling asleep in bed on top of it. Also, if you stand next to a refrigerator with a big open door, I’ve had patients turn their DBS off that way inadvertently.

    And the other thing is, yeah, you want to be careful with airport security. It can either turn the DBS off or affect the settings. It tends to be more so with older batteries, not so much with the new ones. But yeah, you have to be patted down in the airport instead of going through the airport security.

    I heard that you can hack heart pacemakers. Could you conceivably hack a brain pacemaker?

    Not that I know of. I’d have to look into this because I’m not a cardiologist, but I’ve been told that cardiologist can influence the settings remotely. We currently cannot do that. So I would say, at present, you can’t hack in because the only way I can program the brain DBS is that the patient has to physically come into my office, I have to hold this little device that communicates on top of their chest so that there’s skin-to-skin contact, and that’s the only way I can interact with it.

    Whether they would ever change that technology, and then you would have the potential to hack, is an interesting question, but right now, I would say you can’t do it.

    Do leads every detach or start misfiring with DBS?

    Yeah, there are mechanical issues that you can have. There is a chance of lead fractures. If you have a bad fall or something, could you crack one of the wires or could you have some sort of damage to the device? Yeah, it’s a machine with components, like anything else, and the wires can break. It’s very unusual, but it can happen.

    "If you have an accident, think of your brain like a big Jello mold and think of the lead as suspended fruit in the Jello mold—it all moves at the same velocity."

    If it does, it’s rare to have it break in the head, if that makes sense. It’s anchored down in the skull and the wire is going into the brain. If you have an accident, think of your brain like a big Jello mold and think of the lead as suspended fruit in the Jello mold—it all moves at the same velocity.

    The wire doesn’t move within the brain—that’s a question I get asked all the time. But the stuff that’s hooked from the skull on out is usually where the breaks occur. You take the other stuff in the neck going into the chest out and then put a new wire in and you’re good to go. You don’t have to undergo brain surgery again.

    With heart pacemakers and internal defibrillators, it seems like major heart surgery every single time something comes loose. If the battery needs replacement, that’s major surgery as well.

    [Battery replacement] is a same day surgery. The batteries last somewhere between three to five years, but you could be asleep for that. What happens is the patient comes in in the morning and you cut a little slit about three to four centimeters long. You pop the battery out while they’re asleep. You put a new battery into the chest. You hook it up to the wires that are dangling down, that are coming from the neck.

    It’s kind of like when you’re putting in drywall: you’re putting in the electrical wiring, you put a hole in one end of the drywall, you pass the wire behind the wall, and then it pops out the other side. That’s what you do in the brain: you have the wire up in the head and you have another hole down in the chest, and you feed it under the skin until the wire pops out of the chest. You’ve got a battery stitched down into the pectoralis muscle, their chest wall muscle, and you just hook up the dangling cable into that battery. You could be asleep for that. That’s different than brain surgery.

    So you have to be awake for the brain part of the surgery?

    Yeah, usually I have to tell people that. That’s something that may change in the future. There are some trials that are going on to test that. But right now, what you do is you take really good pictures to figure out where to go by planning with a CT/MRI. But even after, there’s still room for error. You could still be off by a couple millimeters because we’re talking about structures like the STN, which is five to seven millimeters long. These are really tiny things in your brain.

    You really want to make sure you’re putting this lead in the right place because it’s going to be there the rest of their lives. So what you do is, you’ve got the lead and you’re suspended above the head. You drill a little hole the size of a dime and it’s like ice-fishing. You anchor your wire to your coordinates from your MRI and you put it, like a protractor, at a certain angle and start driving it down. It slowly goes down bit by bit by bit until the tip of it would eventually hit your target brain structure.

    But the whole way down, that wire can read electrical activity. Your brain is an electrical organ and the neurons are firing. You can hear the patterns of firing on a little machine and you can hear the brain activity of the different targets. They all have a different signature, a different static-y kind of noise. So as you go through the targets one by one, you can identify what structure you’re in by how it’s sounding and looking on this machine.

    We’re testing the patients too and having them do something while they’re awake in the OR. If they move their arm, you can hear the brain firing as they move their arm. Plus, you actually test them once you put the electrode in. You can watch some of the features of Parkinson’s right there on the operating table. You can actually see it get better.

    When I’m awake during dental procedures and I can hear them grinding at my teeth, it freaks me out, let alone if I can hear someone opening a hole in my brain.

    Yeah, so your brain is interesting. Your brain receives all the input from pain elsewhere in the body. So when you hurt your hand, your brain is processing the pain and telling you its unpleasant. But your brain itself, believe it or not, does not feel pain. The structures around it do.

    Your skull will feel pain; the dura, which are these linings of the brain, they feel pain—that’s part of the reason you can have headaches. What you’ve got to do is kind of like the dentist: when you go to the dentist, they numb up the surrounding structures and then they do the root canal. So when you get brain surgery like DBS, they give you all these local injections that numb up your skull and the skin so all you do is you feel pressure.

    "You turn the stimulator on and I have them write or hold something right there in the OR and the tremor dissipates right in front of us. The patients are actually tearing in the OR because they know they’ve finally been fixed."

    We make sure that the team is there talking to you so you feel calm and not scared. We’re saying, “This is what we’re doing, now we’re listening to your brain activity, now I’m going to move your hand.” You’d be surprised. It’s scary, but patients aren’t hurting, they’re not in pain. They’re listening to the brain activity, they’re participating, they’re realizing that we’re going to make sure they feel better.

    Sometimes people are in tears on the operating table because they’ve had this lifelong tremor. You turn the stimulator on and I have them write or hold something right there in the OR and the tremor dissipates right in front of us. The patients are actually tearing in the OR because they know they’ve finally been fixed. It’s an interesting experience.

    There’s a reason you go into neurology. It doesn’t get much cooler than this. We do a lot of great things and you treat people who are sick and you make them well. I mean, that’s why you go into medicine. But if you’re going to do medicine, you could do medicine and then you could do medicine, when you’re actually stimulating the brain, like on Star Trek, you know?

    After they get the DBS, they come by for an office visit. You program them in the office and I can do all sorts of things just by holding this machine in my hand. You are really affecting brain activity with a device in your hand that’s plugged up to a wire that’s in their brain.

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