A Brain-Machine Interface for Regaining Control of a Paralyzed Arm: A Primate Model of Cortically Controlled Functional Electrical StimulationPublic Deposited
A critical challenge in improving the quality of life for spinal cord injury survivors is to restore the capacity to grasp and manipulate objects. While progress has been made to restore hand function by using functional electrical stimulation (FES) to activate muscles, providing the means to control the multiple degrees of freedom needed for dexterous manipulation of objects remains a serious limitation. Here we use a monkey model to describe a novel FES system which uses information extracted directly from the brain to control implanted muscle stimulating electrodes. We show that multi-electrode recordings from the primary motor cortex can be used to predict arm and hand muscle activity (EMGs) in monkeys during complex reaching tasks. These predictions routinely account for 50-75% of the variance of the EMG signals. Furthermore, the predictions can be made successfully for different types of arm movements, and over time periods as long as two weeks. We also show how grasping FES systems can be studied in rhesus monkeys by using a fully implantable drug delivery assembly. This assembly, which consists of a nerve cuff and a subdermal injection port, is used to temporarily block the median and ulnar nerves, and the resulting motor deficits can be used to test how well the monkeys can control FES in the arm and hand. We then show how two monkey subjects were able to use a brain-machine interface (BMI), based on the cortical-EMG models, to control muscle stimulation and regain voluntary wrist flexion following partial limb paralysis. Using this cortically-controlled FES system, the monkeys were able to approximately double their maximum voluntary wrist force, and could grade the muscle stimulation to match targets at different force levels, at speeds of only one-half to two-thirds normal. These results provide an important proof of concept, demonstrating the feasibility of BMI control of grasping FES prostheses. Such systems would offer a significant advantage to patients with injuries in the mid-cervical spinal cord, and potentially even greater benefits to high-cervical spinal cord injured patients with paralysis of the entire upper limb.