“A brain implant has allowed paralysed monkeys to move their limbs by tapping into their thoughts and redirecting the signals to their muscles,” The Guardian reported. The newspaper says this is a major development in the search for treatments for people paralysed due to spinal cord injuries or stroke. It said that there is hope that in the future, disabled people will be able to control of their limbs by using the implant. Several newspapers report different timescales for when the treatment might start being used in humans.
This was a letter to a journal, which describes an experiment and its findings. It found that a monkey's paralysed wrist can be controlled by electrical signals artificially routed from the brain. Similar experiments have been carried out in the past. This research is new in that it managed to divert the signal from just one neuron (nerve cell) to a paralysed muscle to produce movement. The researchers say that moving a muscle is one thing, and producing multiple joint and muscle movement to give coordinated action is far more challenging. Nature reports the authors saying that “clinical treatments may still be many years away”. One thing that needs to be overcome is the size of the implant, which is currently unsuitable for humans.
Chet T. Moritz and colleagues from the Department of Physiology and Biophysics and the Washington National Primate Research Center, University of Washington, in the US carried out this research. The work was supported by grants from the National Institutes of Health. The study was published in the peer-reviewed science journal, Nature.
The researchers say that a potential treatment for paralysis caused by spinal cord injury is to route the brain’s control signals around the injury by artificial connections. These signals could then control muscles by electrical stimulation, and restore movements to paralysed limbs. To investigate this, the researchers used two macaque monkeys between four and five years of age.
The researchers first implanted a number of electrodes in the motor cortex (the part of the brain involved with movement) of the two monkeys. Each electrode picked up signals from a single nerve cell, and the signals were routed through an external circuit to a computer. The signals from the nerve-cells controlled a cursor on the screen, and the monkeys were trained to move the cursor around using only their brain activity. They were rewarded for their success. The strength of the monkeys’ wrist movement was also monitored.
After the monkeys had been trained, the scientists temporarily paralysed their wrist muscles using a local anaesthetic injected around the main nerves in the arm. They re-routed the signals from the electrodes to deliver electrical stimulation to the wrist muscles, a technique known as functional electrical stimulation (FES). The electrical stimulation was tuned to ensure that the wrist moved appropriately. The researchers then assessed the peak performance of the monkeys as compared to their performance during two minutes of practice.
The scientists reported several results from their research. They found that the monkeys could control their previously paralysed limbs using the same brain activity that was used to direct a cursor on the screen. The monkeys could perform this task using virtually any part of the motor cortex. When the nerve signals were re-routed so that the muscles in the monkeys’ wrists were stimulated, they learnt to move their wrists in less than an hour. With practice, the monkeys' performance at this also improved.
The researchers comment that “further development of such direct control strategies may lead to implantable devices that could help restore volitional [voluntary] movements to individuals living with paralysis”.
This research further extends the possibilities in this field of research. The researchers say that, compared to the previously investigated way of using signals from whole areas of the brain to control movement, their technique of using direct signals from single cells to individual muscles might be more efficient. This may also provide the brain with more distinguishable information about what happens when the cells activate, which could aid innate “motor learning mechanisms to help optimise control of the new connections”. This means that they thought the feedback, delivered at a finer level of control, might explain how the monkeys learnt motor skills so rapidly.
The scientists are reported as saying that long-term implants are not yet practical for human subjects, and there is a way to go before the coarse movements at the wrist can be turned into useful activities. Studies such as these do illustrate the future possibilities for such technologies, whether robotic arms or implanted chips. The hope is that they may quickly be translated into practical help for people living with paralysis.