Human brain implants with a sheet rather than an electrode

Here is a different approach to measuring brain activity in humans. Researchers in Japan are placing a sheet of electrodes inside the skull but on top of the cortex.

Researchers at Osaka University are stepping up efforts to develop robotic body parts controlled by thought, by placing electrode sheets directly on the surface of the brain. Led by Osaka University Medical School neurosurgery professor Toshiki Yoshimine, the research marks Japan's first foray into invasive (i.e. requiring open-skull surgery) brain-machine interface research on human test subjects. The aim of the research is to develop real-time mind-controlled robotic limbs for the disabled, according to an announcement made at an April 16 symposium in Aichi prefecture.

Although brain waves can be measured from outside the scalp, a stronger, more accurate signal can be obtained by placing sensors directly on the brain -- but that requires open-skull surgery, making it more difficult to recruit volunteer test subjects.

The researchers, who have filed a license application with the Osaka University Hospital ethics board, are working to enlist willing subjects already scheduled to have brain electrodes implanted for the purpose of monitoring epilepsy or other conditions. The procedure, which does not involve puncturing the cortex, places an electrode sheet at the central sulcus, a fold across the center of the brain near the primary motor cortex (which is responsible for planning and executing movements).

These are not the first researchers to implants devices directly into the human brain. The Donoghue lab at Brown has done electrode implants into the human motor cortex and published results. However, their electrode arrays are much smaller than the sheet of electrodes that we are dealing with here.

There appears to be a degree of trade-off involved. You can sample more brain if you use the sheet, but you can get more cellular resolution if you use the electrodes. The sheet is probably slightly less invasive because you don't have to pierce the pial or subarachnoid layer of meninges. (I don't know this for sure, but it doesn't sound like it.)

There are also researchers who are attempt to use recordings from outside the brain to drive machines. Mo posted about using what is in effect an EEG to drive a character in Second Life.

I am happy to see that there are a plurality of strategies being employed to form brain-machine interfaces. If we could get away with just recording from outside the skull -- if that would provide enough information to run a prosthetic arm for instance -- that would be great. Neurosurgery is a risky thing. On the other hand, such recordings may just not carry the necessary information. It could be that we just have to get really good at doing superficial neurosurgery safely.

The researchers are trying to balance invasiveness with information content. We'll see how successful their attempt is.

(I have to say that I am a bit skeptical that this will provide a lot of useful information. The problem is that you are trying to measure the relative amount of activity in different parts of the motor cortex (and somatosensory cortex). To get the best resolution, you have to get different parts active at different times, not general activity. This works better if you are dealing with a motor cortex that discretely represents each muscle -- the so-called motor homunculus. However, some research suggests that the motor homunculus doesn't exist. Muscles are not discretely represented, so it remains to be seen whether useful information can be gathered in the absence of cellular resolution. A lot will depend on how dense their electrodes are.)

Hat-tip: Slashdot