Fig. 3: Challenges of resolution and coverage in BMI and prosthetic applications.

Illustration of functional mapping in human BMI and prostheses. a Schematics of the central nervous system; implant locations of example applications are marked with black rectangle. b For sensory BMI, one Utah MEA only covers a 4 × 4 mm² region, while human brain uses about 2 × 3 cm² to represent a single-hand in the somatosensory cortex¹⁵⁷. Each colored region in the cortical map corresponds to a certain finger from which it receives perception. c Two Utah MEAs implanted at different sites on a visuotopic map of the visual cortex, which is about 15 cm², and the conceptual illustration of their elicited phosphenes in the vision field¹⁵⁸. Although the resolution of a single phosphene can be less than 1 degree, achieving an average resolution equivalent to the threshold for legal blindness (0.16 degrees across a 20-degree visual field) remains a distant goal. d Three spinal cord segments responsible for controlling the lower limb. Currently, standard epidural arrays, such as the Medtronic 5-6-5 paddle lead¹¹⁶ recruit multiple motor pools and generate global movements of a large muscle group. They lack the precision to target individual rootlets and control specific muscles separately. Each colored spinal cord root controls a group of muscle of the human lower limb with the same color. Middle panel adapted from ref. ¹⁵⁸ licensed under CC BY 4.0.