Brain-Machine Interface or Brain-Body Interface? How to Best Exploit the Remarkable Adaptive Competence of the Brain
Neural prostheses and other devices containing brain-machine interfaces have attracted significant public attention in recent years. This level of interest is beneficial, but people should be careful lest the hype exceed the underlying science. Exploring brain-machine interfaces has become a popular area of research among those attempting to treat paralysis, but some scientists are beginning to consider alternative strategies such as artificial brain-body interfaces.
Today’s state-of-the-art brain-machine interfaces detect cortical activity using electrodes implanted in the skull and then convey this information to a decoding device connected to an artificial actuator. The artificial actuator might be a robotic arm or the cursor on a computer screen. The decoding device is essentially an interpreter that translates brain activity into some sort of action. This decoding is difficult to accomplish, and its usefulness is inherently limited for a number of reasons. First, the brain is not directly controlling anything, and all “learning” over time takes place in the decoding device. Second, the decoding device can only do what it has been programmed to do. In short, brain-machine interfaces cannot be easily generalized to new tasks.
An alternative to the brain-machine interface is the brain-body interface. The idea of a brain-body interface is relatively simple. Instead of passing brain signals to an artificial actuator, brain signals are passed through an amplifier to an electrode capable of directly stimulating muscle contraction. Unlike a brain-machine interface, a brain-body interface uses natural actuators and allows the brain to plastically adapt to the interface over time. Potential problems with this approach involve the fact that muscles are “messy” actuators, but the benefits of building a functional brain-body interface would be substantial. Instead of controlling a robot or cursor, a paralyzed patient would gradually be able to regain control over his or her body.
Functional electrical stimulation (FES) is a technique that could be a useful part of a brain-body interface. The technique involves electrodes that deliver electrical impulses to nerves attached to paralyzed muscles. Connecting an FES electrode in the arm to an array of cortical electrodes in the brain would allow signals from the brain to bypass damaged nerves in the spine. Evidence from other forms of neurological surgery suggests that the motor cortex would quickly learn to control the muscles connected to the brain-body interface.
Researchers such as Robert Ajemian, PhD, and Jonathan Winograd, MD, are currently exploring brain-body interfaces. They have developed a reversible primate model of paralysis, and they plan to use this model to examine the effectiveness of a brain-body interface featuring functional electrical stimulation.
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