This story is from the category The Brain
Date posted: 21/10/2007
A group of researchers at Hebrew University have taken a novel approach to the measurement of brain activity, which is opening possibilities as to how one day a metal-and-plastic limb might operate just as effectively as its flesh-and-blood prototype - and, in the process, teach us more about how the brain interacts with the body.
In an article recently published in The Journal of Neuroscience, neurophysiologists Eran Stark and Prof. Moshe Abeles describe how their new method for measuring and deciphering the electrical activity of nerve cells neatly side steps many of the drawbacks of conventional approaches.
Normally, a mesh of electrodes are placed onto the surface of the scalp, or fine intra-cortical wires are implanted into the brain itself. One of the problems is that the signals produced, are uniform ? the devicescannot differentiate between several neurons immediately adjacent, firing. So, they have to ?guestimate? to a high degree.
This guessing results in a fuzziness of control. The control is there, but fine, precise movement is not possible, and the signals lack any fidelity.
Worse, the intra-cortical implants cause scar tissue to form inside the brain, causing damage, and masking the very activity they aim to measure.
The new approach being undertaken, approach involves measuring the activity of all nerve cells located at an intermediate distance (100-200 micrometers) from a recording electrode. In this way, multiple independent readings can be obtained from many adjacent points, allowing very high fidelity, and the detection of even a single neuron firing amongst hundreds, also firing.
This accuracy makes a virtual, or prosthetic body as accurate as a natural one, a realistic prospect for the first time.
In testing the approach, the researchers trained monkeys to perform what are known as "prehension" movements, reaching and grasping various objects located at different positions. Such actions are complex, requiring the brain to simultaneously regulate direction of reach, performed mainly by the arm, and the type of grasp, performed mainly by the fingers. Using the new techniques, the group found that the upcoming reach direction and grasp type could be predicted at an accuracy of about 90% and, in some cases, at a near-perfect accuracy (above 99%). Overall, the rate of prediction error was two to three times lower than that encountered in existing methods of brain activity measurement.
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