This is your brain on electromagnetic pulse

In general, I want to know what the stuff I'm studying really is, and the only way to know that is to try everything myself. I'm sort of the opposite of my old grandma who would say to the doctor "I'll take those pills if I see you take one first!" Anyway, I've had chances to play with the scanner a little bit so far, and probably more will come as time goes on. But one thing that seems very interesting to me is transcranial magnetic stimulation (TMS). This is, literally, a focused electromagnetic pulse directed at a precise area of the brain; the pulse induces electrical current in the neurons in that area, which causes them to fire. Repetitive transcranial magnetic stimulation (rTMS; for some reason brain researchers are fond of the lowercase acronym prefix, like fMRI, even though it's completely stupid) extends this by providing a series of pulses in rapid succession, perhaps 10 per second. This has the effect of making the neurons fire all at once, but then preventing them from firing after that. So, in effect, by varying the pulse timing, you can do either excitation or inhibition. The particular study I volunteered for is using rTMS to try to show that certain areas of the brain, when inhibited, reduce performance on a simple working memory task, remembering the locations of dots on the computer screen. But that is beside the point; I volunteered for the sake of the experience, for my own knowledge.

The grad student running the study is very cool, and very inquisitive himself. I asked if we could play with the equipment after the experiment, and he was all in favor; he scheduled us for a big open slot on the equipment so we'd have plenty of time.

How do you know where in the brain you're pointing the stimulator's paddle? This is addressed with some remarkable technological wizardry. The setup is controlled by a computer system with a pair of infrared cameras mounted a fixed distance apart on a positionable arm. The subject (me) wears a pair of dorky glasses with a triad of retroreflective spheres, and the computer system uses essentially the same technology as Hollywood motion capture for computer special effects. There is also a wand with spheres on it that the operator uses to identify landmarks on the subjects head. The camera position data is combined with a high-resolution MRI scan of the head, including the skin surface as well as the brain; the scan is reconstructed into a bust floating on the screen; the operator touches the tips of the tragi in the ears (the pointy part in the middle that holds earplugs in place) and the bridge of the nose with the wand; and the computer then instantly positions the bust relative to the stimulation wand, which is also tagged with retroreflective spheres. After that, the operator can peel the surface layers off the bust to expose a view of the brain (it's kind of fun watching your own head get peeled down on the computer screen) and the computer shows a color-coded display of magnetic pulse location and intensity overlaid on the surface of the brain, which tracks the motion of the paddle in real time, even if your head moves. Very cool!

The pulses create electrical stimulation within the focus area of the magnetic pulse; since the pulse is coming from outside the head, this also includes whatever is between the stimulator paddle and the brain. This doesn't matter much unless the intervening tissue happens to contain a major nerve, which is rare, or muscle tissue, which is practically unavoidable. The most readily noticeable effect of TMS is the twitching or clenching of the muscles around the area of stimulation. This can be pretty crampy and painful with high-level or highly repeated stimulation, but, frankly, it's not the biggest sacrifice I've ever made in the name of Science. So it's not too bad. I asked the grad student and he said very few people back out because of the discomfort.

The first procedure is calibration for your particular sensitivity to the pulses. The operator uses the navigation system to aim the pulses at the thumb area of the primary motor cortex; the thumb is attached to an electromyograph to measure any muscle activity, and the pulses are turned down to the threshold where motor activation is barely detectable from brain stimulation. Of course, you start at a high enough level that response is guaranteed, so this is the first fun part, because your arm twitches or jerks with the pulses, which is nice confirmation of the idea that the brain is somehow involved in the control of the body, even if sometimes I wonder if my own behavior is consistent with the idea of control by something as clever-sounding as a "brain".

Then there's the long, tedious experiment. The goal of collecting lots of data is kind of in conflict with the goal of making the experiment exciting, so excitement loses out.

At the end, we played around. When I first met the TMS people, they were talking about playing with "speech arrest", where you stimulate Broca's Area, the area responsible for speech generation, and you can't talk anymore. We tried this on me, but nothing happened. I asked to try to visual cortex; you should be able to generate phosphenes, which is a very old general term for flashes of light seen as artifacts of electrical activity, but this didn't work either. So I asked if he knew about Persinger's "God Helmet"; do you know where you are supposed to stimulate my brain so I see God? He said that should be right about here, and we tried that too, but it didn't work either.

He said he'd look into the literature on these things before I came back for the second session. He didn't get around to it, but while I was doing the tedious task again he looked up the parameters for speech arrest and this time it worked. I started counting "One two three four" and hit the "go" button for a 1-second series of pulses and "five skthbl blwwwwwh..." Wow! That's really cool. I kind of wanted to try that again, with longer series of pulses, but it was kind of painful and, well, I got the idea pretty well. So we tried the visual cortex again, with this higher intensity, but nothing. And I didn't see God either, unfortunately. But maybe I'll have another shot at that next week.

Another demonstration he likes to do is to pulse an empty soda can with the paddle. The pulse is strong enough to send the can flying across the room, he says, but I keep forgetting to bring a can so we can try it out. It's a good thing the brain isn't made of aluminum. When I get around to getting a new cell phone, I want to pulse my old one. It will certainly kill it; it might even set it on fire, which he was concerned about, although I'm sure we can manage whatever comes up.

So, that's my brain on electromagnetic pulse.