Cyborg Monkeys and How the Brain Controls the Body

May 29th, 2008 | By | Category: Lit Round-up

Thanks to our continuing success in Iraq, you might have noticed distinctly fewer limbs in today’s America. Hence this recent work published in the journal Nature is quite encouraging:

Here we describe a system that permits embodied prosthetic control; we show how monkeys (Macaca mulatta) use their motor cortical activity to control a mechanized arm replica in a self-feeding task. In addition to the three dimensions of movement, the subjects’ cortical signals also proportionally controlled a gripper on the end of the arm. Owing to the physical interaction between the monkey, the robotic arm and objects in the workspace, this new task presented a higher level of difficulty than previous virtual (cursor-control) experiments. Apart from an example of simple one-dimensional control, previous experiments have lacked physical interaction even in cases where a robotic arm or hand was included in the control loop, because the subjects did not use it to interact with physical objects—an interaction that cannot be fully simulated. This demonstration of multi-degree-of-freedom embodied prosthetic control paves the way towards the development of dexterous prosthetic devices that could ultimately achieve arm and hand function at a near-natural level.

The big plan here? Brain cells make electrical currents when doing their jobs. By listening for these electrical spikes with electrodes, we can eavesdrop. Using a map of the brain, giving us a clue which part of the brain controls (or controlled) the limb, we can put the electrodes over the right spot. When we detect a change in the brain cells in this spot, we can move a robot arm. Enjoy your new cyborg limb!
Well, Meel Velliste et al got a monkey to move a robotic arm just by thinking. Nifty. Many groups, including my buddy Kai Miller right here in Seattle, have gotten people to play video games just by thinking. This brings us one step closer to replacing all those lost limbs.
Still, we really don’t have the best idea of exactly what these brain cells must say to one another when they want to move a limb or a finger. The better we understand this language, the better we can program the computer sitting between the electrodes on the brain and the robotic limb. Back to my friend’s thesis defense this week.
Listening to the brain with these electrodes, that read millions of brain cells at a time, is a bit like listening to the crowd at a stadium. You can hear large groups chanting in unison, horns or general roar; trying to pick out an individual conversation in all of this is next to impossible.

Still, we can figure a lot out at this level. When parts of the brain are at rest, they’re subject to regular gonging. The idea is somewhat like the best scene in Blazing Saddles (“Dag namit. The sheriff is a n{GONG}…”) Every time the part of the brain starts getting an idea to activate out of turn, the gonging from deeper levels interrupts the planning. So, the absence of this gonging is one way to detect when a part of the brain is activated. The problem is, this happens over a huge area of the brain. We need to figure a way to listen in on the planning among the brain cells that can now proceed uninhibited. A good old-fashioned scientific knife fight emerged in the field. One camp figured this planning would be synchronized–like a section in the stadium starting to chant, “Wave! Wave! Wave!” The other camp figured it’s hard to plan anything by only chanting in unison. Any meaningful planning would be the brain cells taking to one another, out of sync, and thus just sound like a bit louder roar from a small section. Screw listening for chants, listen for an increase in crowd noise and you’ll figure out when the brain is trying to, say, wiggle a finger.

My friend, sifting through recordings from human brains and using complex mathematical earplugs to separate the raw data from the electrodes into manageable pieces, figured out the second camp is probably right. Listen for the roar!
Two fun advances in science at a timely moment.