Next Step for BMIs
Brain Signals from One Primate Move Paralyzed Limbs in Another Primate
Researchers from Cornell’s School of Electrical and Computer Engineering and Harvard Medical School’s Department of Neurosurgery have developed a new neural prosthetic that uses neural activity recorded from premotor neurons to control limb movements in functionally paralyzed primates. This is a step toward making brain-machine interfaces for paralyzed humans to control their own limbs using just their brain activity. Previous research has been limited to controlling external devices such as robotic limbs.
The researchers describe a cortical-spinal prosthesis in their paper that directs targeted movement in paralyzed limbs. The research team developed a prosthetic that connects two monkeys, enabling one monkey to send its recorded neural activity to control the limbs in a different monkey that is sedated. When paralyzed patients imagine a movement, neurons in the premotor cortex still activate even though the link between the brain and muscles is broken. Neural activity recorded in these brain areas can be translated to movement using a decoder. Such an interface could allow patients to generate movements just by thinking.
The basis of the brain-machine interface is a set of real-time decoding algorithms that process neural signals by predicting their targeted movements. One monkey acts as the controller of the movement, deciding where to move to, creating specific neural activity. The decoded neural activity is then used to electrically stimulate the spinal cord of the other monkey, controlling its limb movement. The difficulty in accomplishing this task comes from a combination of decoding the recorded neural activity into the intended movement along with correctly stimulating the spinal cord to move the paralyzed limb.
The researchers focused on decoding the target endpoint of the movement rather than the exact sequence of movements. This allowed them to match the decoded target with specific spinal stimulations that generated limb movement toward the target. The results show that the alert monkey could produce two-dimensional movement in the sedated monkey’s limb. Focusing on the target endpoint reduced the complexity of solving the required spinal stimulations. Using two different animals, rather than a single temporarily paralyzed one is a more realistic model of paralysis, since the brain and the limb had no physical connection.