Synthetic Touch for Brain-Controlled Bionic Hands: Tactile Edges and Motion via Patterned Microstimulation of the Human Somatosensory Cortex

Book chapter, 2026

RATIONALE: Intracortical microstimulation (ICMS) of the primary somatosensory cortex (S1) can generate distinct tactile sensations, with their characteristics and spatial locations modifiable through adjustments to the stimulation site and parameters. Although this technique has been employed to provide sensory feedback in brain-controlled prosthetic limbs, the resulting touch experience remains limited, restricting fine motor control. To overcome these constraints, we aimed to enrich artificial tactile feedback by encoding additional sensory dimensions—specifically, object geometry and motion—drawing on established principles of somatosensory encoding and stimulation techniques used in other sensory systems.METHODS: We began by applying spatially structured ICMS across multiple electrodes whose projected fields (PFs)—the perceived locations on the skin—were aligned. We then extended this approach to include patterns representing complex two-dimensional, curved, and three-dimensional shapes. Additionally, we introduced temporal dynamics by stimulating spatially separated PFs in sequence, mimicking the sensation of movement. These strategies were integrated into a brain-machine interface controlling a bionic arm to assess their practical application.Results When stimulation was applied through electrodes with linearly arranged PFs, participants spontaneously perceived an edge. With more elaborate spatial patterns, users reported intuitive recognition of various geometric shapes. Temporal stimulation across adjacent PFs induced vivid sensations of motion, with direction and speed modifiable by electrode selection. Importantly, in a functional setting, a participant using a neurally-controlled prosthetic arm successfully utilized these patterned stimulations to perform an active task, guided by artificial sensory feedback. Conclusion Carefully designed spatiotemporal ICMS patterns can evoke complex and nuanced tactile percepts, including shape and movement, greatly expanding the scope of artificial touch. These advancements pave the way for more natural and effective sensory feedback in neuroprosthetic systems.