In February 2012, scientists and clinicians based at the University of Pittsburgh in the USA implanted two microelectrode arrays [1] into the left motor cortex [2] of the participant, a 52-year old woman who had been diagnosed with spinocerebellar degeneration [3] thirteen years earlier. Due to the progression of her disease, the participant is now tetraplegic, meaning that she is paralysed from the neck downwards, and cannot voluntarily move her arms or legs.
The electrode arrays in the participant's motor cortex were connected to a robotic hand, with joint and wrist movement comparable to a human hand. After the prosthesis had been connected, 14 weeks of training took place, in order for the participant to learn to use the device. However, although it took several weeks to master performance, the participant was able to move the prosthetic hand freely without the aid of a computer on just the second day of training, two weeks after implantation.
This unprecedented speed of adaption to the prosthesis is partly attributable to an innovative new way of connecting the participant's brain to the prosthesis, as Professor Andrew Schwartz, lead author of the study, explains: "In developing mind-controlled prosthetics, one of the biggest challenges has always been how to translate brain signals that indicate limb movement into computer signals that can reliably and accurately control a robotic prosthesis. Most mind-controlled prosthetics have achieved this by an algorithm which involves working through a complex 'library' of computer-brain connections. However, we've taken a completely different approach here, by using a model-based computer algorithm which closely mimics the way that an unimpaired brain controls limb movement. The result is a prosthetic hand which can be moved far more accurately and naturalistically than previous efforts."*
A comprehensive training and testing programme took place, lasting for over three months, and with the aim that the participant should ultimately be able to complete tasks showing that she could control the prosthesis over seven degrees of freedom [4]. Over time, the participant was able to complete the requested tasks with a success rate of up to 91.6%, and over 30 seconds more quickly than at the start of the trial. For the first time, the researchers used standard tests – called Action Research Arm Tests (ARAT), and usually used to assess limb function after paralysing events such as stroke – to show that the improvement achieved was clinically significant, an important step which will allow future developments in similar prostheses to be objectively evaluated.
According to the authors, the next steps in improving this type of thought-controlled prosthetic include incorporating sensory elements – so that the patient might, for instance, be able to tell the difference between hot and cold, or smooth and coarse, surfaces – and also to incorporate wireless technology, removing the need for connecting wires between the patient's head and their prosthesis.
Writing in a linked Comment, Professor Grégoire Courtine of the Swiss Federal Institute of Technology Lausanne (EPFL) says that, "This bioinspired brain-machine interface is a remarkable technological and biomedical achievement. Though plenty of challenges lie ahead, these sorts of systems are rapidly approaching the point of clinical fruition. Through concerted efforts, and by ensuring that various different strategies available are optimally combined, these kinds of prosthetics might soon become revolutionary treatment models for sensorimotor paralysis."*
NOTES TO EDITORS:
[1] A microelectronic device which connects brain cells (neurons) to electronic circuitry
[2] The motor cortex is the part of the brain which initiates movement
[3] Spinocerebellar degeneration is a genetic disease where structures in the areas of the brain and spinal cord that control coordination degenerate and eventually lose their function
[4] ie, three-dimensional translation (moving from one point to another), three-dimensional orientation, and one-dimensional grasping
* Quotes direct from authors, and cannot be found in text of Article / Comment
Journal
The Lancet