Science Interviews


Sun, 15th Jan 2012

Wiring the Brain to Robotic Limbs

Professor Andrew Schwartz, University of Pittsburgh

Listen Now    Download as mp3 from the show Mind Meets Machine

Chris -   Scientists are moving closer to developing ways to interface with the brain and to decode what nerve cells are saying to each other.  Professor Andrew Schwartz is working on this at the University of Pittsburgh and he’s with us now.  Hello, Andrew.

Andrew -   Hello.

Chris -   What sort of signals are you trying to eavesdrop on?

Andrew -   Well, we record from a part of the brain called the motor cortex and this part of the brain is thought to have a lot to do with controlling movements.  We’re particularly interested in arm and hand movements.  So the neurons we record from seem to be related to aspects of moving the hand and arm, and particularly the direction and speed in which the hand moves.

Chris -   In other words, if you were to look at the surface of the brain and specifically the bit of the brain that we know relates to movements, there's a map of a person, or the body, on the surface of the brain and different bits of that map relate to different body parts.

Andrew -   That's right in sort of a coarse way.  That's a general way of looking at it.

Chris -   So when you are recording from different clusters of nerve cells, what does it sound like?  What sorts of conversations do nerve cells have?

Andrew -   So, we can record from individual nerve cells and the message that they send is the rate at which they fire action potentials.  So action potentials are these little impulses of electricity and the time between those impulses carries the information.  And so, what we’ve found is that, when you move your arm in different directions, that each neuron has a direction in which it likes to fire fastest in.  We can take account of that to try to decode the way that you intend to move your hand.  And so, over the years, we’ve built up a rather elaborate decoding mechanism where we can look at the direction and speed of the arm in 3-dimensional space and more recently, the angle of the wrist and now, the shape of the hand and fingers.  So we can get pretty much a complete representation of what you're trying to do with your hand by tapping into these signals.

Chris -   So rather than just turning individual muscles on and off, these motor cells in the motor part of the brain are active when they want to make a part of the body move to a certain position in 3-dimensional space.  So, in other words, if you wanted to hold your hand out at 45 degrees to yourself, there would be a bunch of cells that would fire the most when you're going to do that.

Andrew -   Right and the interesting thing is it’s not just the cells that like to fire in that direction but the other cells will actually stop firing when you move against their preferred direction.  So what we do is we look at the entire population because all the neurons carry some information about that movement.  So one of the critical things about all this is that we look at the large population of cells, not just at a few individual neurons.

Chris -   It’s quite clever, so you're looking at things going off as well as things turning on.  How many nerve cells do you record from?  If you want to decode meaningfully what the brain wants to do, how many electrodes do you need?

Andrew -   Well, we’ve used as few as 30 neurons to get a good representation of X, Y, and Z movement – 3-dimensional movement in space.  But typically, what we do now is record from 100 to 200 neurons and we get a more elaborate decoding.  So now, we can record or decode other aspects of movement as well.

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