Somatosensory ICMS (touch restoration)
Microstimulation of primary somatosensory cortex (Brodmann areas 1 and 3b), delivered through electrodes in the hand representation, evokes tactile sensations that a person refers to specific parts of their own (often insensate) hand. In human participants with spinal cord injury, ICMS produces focal percepts on individual fingers, most commonly described as pressure, touch or tingling, with perceived intensity increasing monotonically as pulse amplitude or frequency rise.
The clinical significance is that these percepts are stable over months and somatotopically organized, so electrode identity can serve as a place code for finger identity. When integrated as feedback in a bidirectional grasp task, ICMS touch cues roughly halved object-transfer times, demonstrating functional benefit rather than mere sensation.
The honest limitation is that evoked percepts are not yet fully naturalistic: many are paresthetic, the achievable range of qualities (texture, edges, slip) is narrow, and coverage of the hand is limited by the number and placement of electrodes.
A participant reports that stimulating one electrode feels like pressure on the tip of the index finger, while a neighbouring electrode projects to the base of the same finger; the map stays consistent across sessions.
Stable projected fields let a fixed electrode act as a labelled line for one skin location.