Source: Economist
Date: 2 May 2002
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(MP4, 7.3MG)

The brain-in-a-rat problem

Nefarious neuroscientists compel rats to do their evil bidding

IMAGINE robots that can scale stairs, climb walls and jump off trees. Not only can they fuel themselves and clean themselves; they can reproduce themselves to boot. It takes about ten minutes a day, for about ten days, to make one. Most of the hardware is available off-the-shelf, and the total bill comes to about $50. Oh, and one more thing: they're alive.

The "robots" in question are really rats with electrodes implanted into their brains to tell them what to do. An operator sitting at a laptop computer can control the movement of the rats via a transmitter that activates the electrodes. Up to a point, a "roborat" will do whatever its operator instructs - even things that are instinctively repellent to it, such as hanging around in brightly-lit open spaces.

Although the idea sounds shocking, the principle behind the experiment is not new. Three years ago, John Chapin, Sanjiv Talwar and their colleagues at the State University of New York, in Brooklyn, developed a "neural interface" that allowed an animal to manipulate a robotic arm simply by thinking about it. An implant would record the signature of the electrical firing of the subject's nerve cells and relay the information to the arm. Their latest experiment, described in this week's Nature, simply reverses this process. Rather than extracting information from the firing of nerve cells, the new system feeds stimulation to certain cells in a rat's brain in a pattern that coaxes it to move as desired.

The trick lies in getting the right nerve cells to fire at the right time. The researchers trained a rat to move by stimulating part of the brain known as the somato-sensory cortex (this is the region responsible for bodily sensation). When electrodes stimulate a certain patch of this cortex, a rat feels a nudge on its left whiskers. When another patch is stimulated, the nudge is to the right whiskers.

Since rats rely on signals from their whiskers to detect obstacles, Dr Talwar and Dr Chapin were able to use the electrodes to persuade a rat to move one way or the other. To reinforce their false signals, they also sent pulses to a part of the brain known as the medial forebrain bundle (MFB) whenever a rat obeyed. The MFB is the so-called "pleasure pathway" that is thought to be responsible for both the sense of motivation and the sense of reward. Rats worked out that obeying the nudges would produce pleasurable feelings, and quickly fell into line.

Despite appearances, Dr Talwar says that his rats are "not zombies". They retain their native intelligence and when guided towards an obvious threat or a difficult obstacle, they flinch and recoil. With enough MFB stimulation, this hesitation can sometimes be overcome, but occasionally cannot. Of course, he admits, the experimenters never actually tried very hard to push a rat to do something self-destructive or uncomfortable. So the strength of a rat's willpower remains untested.

So, too, does the limit of a human's. In all probability, a similar device could be installed in a human being tomorrow, though Dr Talwar thinks it should be illegal to do so. Whether anybody else will want to have a go - and whether any ethics committee would allow them to try -remains to be seen.

picture of a pair of rats

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