Stopping A Seizure in its Tracks
Chris - Now this week, scientists have come up with a way to use pulses of electricity to stop certain forms of epileptic seizure. György Buzsaki from New York University led this work. It's published this week in the journal Science and he's with us now. Hello, György.
György - Hello.
Chris - First of all, what actually is happening when someone is having an epileptic seizure?
György - There are many kinds of epilepsies. The ones that we use as a model is associated with loss of consciousness, so you're driving in a car and you have an epileptic seizure and you lose complete control of your ability to drive a car.
Chris - Okay, so if we were to record from the brain itself when these seizures are happening, what's going on electrically?
György - In this case, it's very easy to recognise because what happens is, many neurons all of the sudden are enslaved into a common chorus. They just beat together in various synchronised discharges, these signal discharges correspond to the signal as a membrane potential change and this membrane potential change produces very large currents that can be measured even outside the skull.
Chris - And so, once one little group of nerve cells is firing abnormally, this can then spill over onto other adjacent regions of the brain and propagate or reverberate around the brain, disrupting the normal function.
György - Exactly. Reverberation is very appropriate in this form of absence or generalised seizures because what happens is that there's a Ping-Pong mechanism between the thalamus and neocortex. The thalamus sends out a signal discharge, enslaves neurons in the neocortex which in turn send back a reinforcing pattern and it goes on and on, and on and on.
Chris - Until something breaks the cycle. So when people take anti-epileptic medication, what does that do to stop that happening normally?
György - Well, that's the reason why we did this study, is because in order to stop the seizures, you have to do something drastic to prevent this pattern from occurring. The magic drug would,of course, have an impact only when this super-synchronous event occurs.
Chris - So effectively, you've got to damp down the activity of nerve cells to stop the seizure activity, but this is going to have consequences for people when they're not actually having a fit. So the ideal situation would be a way to have a way of arresting the seizure when it's going to happen but not really having it on all the time, and that's really where your paper comes in, isn't it?
György - That's right. So we use an animal model. Luckily, this particular form of epilepsy has an excellent rodent model and so, we were able to record these epileptic patterns that occur hundreds and hundreds of times a day so we could do many experiments. And we've not only detected these seizures, but we detected every single cycle of the seizure. And that's a critical point, becuase the way you can break up a vicious cycle is to interfere, cycle by cycle. So for example, a seizure in the rhythmic pattern is an oscillation just like a swing. You can stop the swing by grabbing the person and that requires a lot of energy, or you can interfere with the swing cycle every single time when the person is up for example. In this case, it's very small amount of energy. You can achieve the same action that eventually, the rhythm that is the swinging will stop.
Chris - So you put a little bit of electricity into the brain when there are signs that a fit is about to happen.
György - So we used transcranial electrical stimulation which are electrodes placed outside the skull and applied currents at the time when we knew that the brain does not have neurons firing, that means we can interfere with this reverberating self-sustaining patterns.
Chris - But do you only turn that signal on when the person is going to have a fit or the animal in this case so that you don't interfere with brain function normally?
György - So we applied the electrical stimulations only during the few seconds of episode when the seizures occurred and never outside.
Chris - In other words, if you only switch this on when the animals having a fit, does this appear to block the progression of that seizure so the animals spend less time fitting?
György - We have to wait until the seizure occurs and this is when we start the stimulation. So, our method doesn't prevent epileptic seizure. It shortens it.
Chris - And so, if you were to translate this to a human, would it work?
György - I would be very surprised if it wouldn't because the principles are exactly the same. There are a couple of technical challenges that have to be applied because the signals that you carry across from outside the human brain to inside the skull are much smaller in the case of in the case of human. So, the technical problems, the electronic problems are larger, but it's solvable.