This story is from the category The Brain
Date posted: 30/05/2008
Caltech researchers are working on developing a MEMS-based (Micro-Electro-Mechanical System) brain-computer interface, with initial designs proving promising, and they already claim that the software side is essentially complete.
Currently, brain-computer interfaces connect to the surface of the brain, and the individual electrodes of the prosthetic chip seek out the strongest electrical signals in the area. Only those electrodes close to a functioning neuron, bind with them.
There is a problem with this method, in addition to the waste that occurs when a large number of electrodes cannot bind due to lack of a strong signal at the implantation site. The brain tolerates the invasion into its network by the electrodes, but the body does not. Over time, a layer of new scar tissue forms around the electrodes, blocking them off from interfacing with neurons.
Over a course of months, once strong electrical signals become deadened as increasing layers of scar tissue build up.
With the MEMEs interface, as the electrodes are driven into the tissue, the software starts monitoring electrical conductivity in the vicinity of each electrode. When a spike is detected, that individual electrode is extended in micron increments, until the signal starts to deteriorate. This ensures each electrode has access to thre strongest signal possible, as each plunges to a different depth.
Continual monitoring also determines which neuron-firings are dampening out, as in covered with scar tissue over time. As the signals fade, the software commands individual electrodes to push deeper once more, punching trough the scar tissue to regain connection.
A side effect of this is obviously that even more scar tissue will form over time, as the implant slowly squirrels its way deeper into the brain. However, the scale is small enough, that even over a lifetime, the amount of scar tissue in comparison to the size of the brain would be extremely tiny, and any loss of brain function entirely negligable. It is doubtful the area affected would be as much as a single millimetre thick, given the scale involved.
The neuron-tracking algorithm was inspired by software the U.S. military uses to track planes, demonstrating a clear example of a breakthrough in one industry being used to assist an entirely separate field.
There is still considerable work to be done, as the prototype pictured above, is close to two centimetres across, for just one single electrode. This immense scale is clearly unworkable, with existing brain-computer interface chips having up to 12,000 electrodes per square centimetre.
It is only a prototype, and much work still needs to be done, notably on shrinking the control hardware, whilst ensuring reliability is maintained. Still, given the pace of neuroprosthetic electrode development to date, and the rapid shrinkage already possible with other designs - in some cases halving in size within a year - it should only be a few years before this design is compact enough to be tested in mice. After that, humans are only a short step away.
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