The post on Bionics and Brain Machine Interfacing will be divided into two parts. Part of this it's because of my ongoing difficulties with carpal tunnel syndrome, any other part is to accommodate some professional travel in which I will actually be working on a related project.
In the previous blog, we discussed the state-of-the-art in visual and auditory prosthetics. Were still a long way from the ideal of The Six Million Dollar Man, and that these prosthetic devices are not yet fully integrated with brain inputs, and cannot completely replace the role of the natural sensory organs. In many ways the science of Bionics, or more accurately neural prosthetics, is still quite primitive and will remain so until several very important factors are resolved. These problems are, in no particular order, complexity of the signals that have to be interfaced with the brain, longevity of the electrodes then need to interface with the brain, complexity of the prosthetic (such as number of pixels in the visual field, or the multitude of movement possible at a single joint), powering the prosthetic, and weight of the prosthetic.
The issue of complexity is made rather obvious from the fact that current visual and auditory prosthetics are unable to render the rich diversity of sight and sound – however this is primarily an issue for density of receptor and stimulation electrode. However when it comes to artificial limbs, there are many factors that must be considered: how many joints, the directions those joints can move, movement of joints in synchrony, and coordinating all of those movements. The problem of appropriate electrodes to interface a prosthetic with the brain is one that will actually be covered in Part Two of this blog which will specifically involve interfacing the brain with external devices.
|"The Six Million Dollar Man", Harve Bennett Productions, 1974|
Some rather astounding work has been accomplished in the past five years that address the remaining factors, particularly with respect to developing a brain operated upper limb prosthetic – in other words, a bionic arm. I have previously mentioned the defense research agency DARPA, which is considered by many to essentially fund "science fiction". In 2007 DARPA funded a project called Revolutionizing Prosthetics. The goal of the program was to develop a brain interfaced upper arm prosthetic, essentially similar to the Six Million Dollar Man prosthetic shown in this picture. One of the principal goals of this project was to develop a "bionic" limb that was capable of complex emotions such as flexing fingers and rotating the wrist, yet was no heavier than a limb made of flesh and blood. The original project in 2007 funded a company by the name of DEKA, founded by Dean Kamen, inventor of the Segway. The project was quite successful, and resulted in a follow-up program which began in 2009, to begin the first tests of interfacing the prosthetic with the brain, culminating in the first patients by 2013. This is a multi-institutional research project, spearheaded by Johns Hopkins University, and involving at least 10 other universities and a similar number of foundations and private companies. The following website provides a short summary of the program (http://www.neurotechreports.com/pages/darpaprosthetics.html), and many of the reports from DARPA can be found in a Google search. Just used keywords "revolutionizing prosthetics".
One question that may be asked at this point, is why the prosthetics program is concentrating on an upper limb or arm and hand prosthetic, and not a lower limb leg and foot prosthetic. A major reason is that at present brain control is not necessary for effective prosthetics for lower limbs. Biomechanical devices that utilize springs and pistons are quite capable of mimicking lower limb function provided some residual portion of the leg below the hip is present. Note that even these biomechanical limbs still meet the definition of "bionic" or lifelike as first defined by Dr. Jack E Steele in the 1950s. The next revolution in lower limb prosthetics will be to provide self motivating legs to replace total amputation from the hip. However the complex motions required to lift, twist, handle, and manipulate objects as required by fingers, wrists, and elbows has placed current emphasis for bioelectronic prosthetics on the upper limb.
With all of the wonderful progress that's being made on prosthetics with this program, a major hurdle is still providing sensory feedback from the limb to the brain. In many ways this becomes a problem very similar to advanced visual and auditory prosthetics. Several of the teams funded by the Revolutionizing Prosthetics program are working on precisely the issue of providing both tactile and proprioceptive feedback. Again, this is largely an issue of interfacing with the brain, which I will address in the next blog.
Until next time, keep humming that Steve Austin theme!