Enabling Advanced Interactions through Closed-loop Control of Motor Unit Activity After Tetraplegia

Studies have shown that most individuals with motor complete spinal cord injuries (SCIs) can activate motor units (MUs) below the injury level, potentially enabling the use of myoelectric controllers for computer tasks. We present a novel wearable neuromotor interface driven by surface electromyography (sEMG). This wearable sEMG interface detects motor unit action potentials (MUAPs) from an array of sensors on the forearm. The MU event rate is translated (i.e. decoded) into discrete or continuous inputs for emulating button presses or joystick inputs. Our study demonstrates real-time detection and decoding of MUAPs in two individuals with tetraplegia, enabling computer task control via a non-invasive interface. Participants calibrated a spike sorting model through periods of rest and tonic activation, mapping MUAP firing rates to various degrees of freedom (DOF) for cursor or character control in tasks and 2D games. Each MUAP was mapped to a separate DOF axis, which we utilized in a Fitts’ Law target acquisition task to evaluate device throughput rate and other performance metrics such as completion rate, initiation time, time to target acquisition, and dial-in time. Our findings highlight MU firing as an effective control input, enabling gaming and social interaction for individuals with tetraplegia. This device’s wearability and ease of use offer an innovative human-computer interaction solution that may enable people with SCI to interact freely with computers and other digital devices.