article written by Melissa Walmesley for andreacollo.wordpress.com
Late last year a woman sat in a wheelchair she had been bound to since a stroke 15 years earlier left her quadriplegic, with no use of her body below the neck. She then reached out, grabbed a cup of coffee and put it to her mouth, taking a sip. This was no miracle, just another step in the growing body of research into neuroprosthetics, a revolutionary technology which can work alongside functional rehabilitation robotics and that will allow paralyzed people the ability to move, feel and communicate again in the very near future.
Brain-Machine Interfaces (BMIs) and Brain-Computer Interfaces (BCIs) are devices that use a neural implant to record and process electrical information from the brain into actions that a computer, robot or virtual avatar can perform. Each implant picks up minute electrical impulses from hundreds of neurons around it. Each time a neuron fires, that is, sends an impulse, that impulse is recorded. The timing of these impulses and the rate at which they occur is correlated to the actions or sensations we want to perform or that we feel. For instance, as you move your eyes to read this sentence, certain cells in your brain increase their firing rate which will signal the muscles surrounding your eyes to produce the correct movement to move your eyes from left to right. These firing rates are then used as inputs into mathematical algorithms developed over many years which try to work out what the intended movement associated with the rate is. Researchers do this by training the algorithm, giving it a set of firing rates of all these hundreds of neurons and a sample of the corresponding movement the firing produced (by simultaneously recoding the position of a joystick a research animal might be moving or recording its position using motion capture software). The algorithm then works out how the firing correlates to the movement. Once the algorithm is trained they give it new data and it can predict what is supposed to happen. This output can then be used to produce a movement, such as a cursor moving on the screen, or the robotic arm moving to pick up the cup.
A symphony of activity – This technique has only recently been made possible by advances in technology that allow the researchers to record from many brain cells at once. The human brain is nothing but a connection of billions and billions of cells and no single cell is responsible for a single action or thought, rather thoughts, actions, feelings are all the combination of ensemble of neurons, all increasing or decreasing their firing at once. Some researchers are already starting to look at ways to record from thousands or tens of thousands of cells simultaneously, even though this is still a tiny fraction of the amount in the brain. It is only when we get to such numbers that we truly start to see how the human brain works as a symphony. There is a number of hypotheses about how the brain is compartmentalized into areas of specialization and some researchers spend their entire lives dedicated to a single square millimeter of brain real estate. However, the brain is a mass of interconnection, so you have to look everywhere to get a feel for how it works. Though most BMI-related work has concentrated so far on movements, researchers want to get a deeper understanding of the entire structure. Areas such as those associated with movement planning and feeling incoming sensations are the most investigated, as well as deeper structures such as basal ganglia and the thalamus (they play a key role in producing body movements and are damaged in such diseases as Parkinson’s disease). Others are looking at implanting devices in memory areas of the brain, addiction centers or pain centers to try and help with memory loss and addiction, or work as painkillers.
Though the field is moving quickly, some advise caution. The pioneering implants in humans have so far all been ‘wired’ implants. That is, they all have a direct connection from the brain to the outside world. For such a technology to really be able to be used in humans it has to be wireless – the chip in the brain has to be able to be sealed in and then communicate wirelessly with any computer or robot in the outside world. The brain exists within its own cocoon within the body, sealed off to prevent infection as much as possible – a direct link through the skin to the outside world would have a strong likelihood of leading to an infection for the patient, who, being in a paralyzed state or injured or having a disease, may well already be in a compromised state.
Feeling as well as moving – The next step in BMI is to use these implants not only for recording the brain activity associated with different movements, but also to try and mimic sensation. If you imagine a person using a neuroprosthetic arm to pick up a coffee cup, not only they have to produce the movement, they also need to feel the cup so they can exert the correct pressure, know how heavy it is and know how hot the coffee inside is. Ideally you would want to be able to send all this information directly back into the brain so the person can use the arm as naturally as possible. Researchers have been able to use such feedback to mimic textures, so that an animal moved a computer avatar arm between different objects and felt them to decide which is the correct object to pick up with the arm. All movements require sensory feedback to be able to be performed correctly and it is a great challenge nowadays to allow people who will eventually use this technology to be able to live lives as rich as possible. Stimulation can be used in other brain areas to produce other body sensations or even emotional feelings.
Neuroprosthetics open up an entirely new field of not only medicine, but possible human experience as implants could be produced to change the way you think, how you remember or what you remember. Caution will be needed, as with any new technology, but currently the benefits have started outweighing the possible downsides of such technology.