After a spinal cord injury the brain still makes the command to walk, but it cannot reach the circuits below the injury. A brain-spine interface carries it around the gap: read the intention from the cortex, decode it, and stimulate the lumbosacral cord. Step through how the 2023 system worked (Lorach et al. 2023).
Two implants sit on the surface of the brain, over the sensorimotor cortex, inside the skull. Each records from a grid of electrodes.
“WIMAGINE implants consist of an 8-by-8 grid of 64 electrodes (4 mm × 4.5 mm pitch in anteroposterior and mediolateral axes, respectively) and recording electronics that are embedded within a 50 mm diameter, circular-shaped titanium case that has the same thickness as the skull.” Lorach et al. 2023
Compare the natural route: a command from the cortex reaches a leg muscle in tens of milliseconds (see the Signal journey). The bridge adds hundreds of milliseconds, yet the participant reported natural control: “The participant reports that the BSI enables natural control over the movements of his legs to stand, walk, climb stairs and even traverse complex terrains.” Lorach et al. 2023