250 Tactile Edges and Motion Via Spatiotemporal Microstimulation of the Human Cortex

INTRODUCTION: Intracortical microstimulation (ICMS) of the somatosensory cortex can evoke basic tactile sensations in patients with paralysis or limb loss, but traditional ICMS has constrained functionality to the simplicity of induced sensations. In this paper, we demonstrate for the first time that precisely patterned and sequenced ICMS can evoke complex tactile sensations including oriented edges, 3D-indentations, and directed motion across the skin. This discovery significantly enhances the functionality and usability of bionic neuroprosthetic devices. METHODS: We conducted experiments on two participants with spinal cord injury by implanting microelectrode arrays in the hand areas of somatosensory cortex. We designed and tested novel neurostimulation paradigms using spatially and temporally patterned ICMS. Participants performed tasks to discriminate edge orientations, identify shapes, and perceive motion. Statistical significance was assessed using Fisher's Exact Test. RESULTS: Spatially patterned ICMS evoked the sensation of an edge, with participants discriminating edge orientation at 85% accuracy for C1 and 65% for C2 (p<0.05). For complex shapes, C1 identified shapes with 82% accuracy on D2 and 72% on D3 (p<0.05). C1 differentiated between concave, convex, and flat curvatures at 64% accuracy (p<0.05). Sequential ICMS evoked motion sensations, with C1 distinguishing motion direction with 76% accuracy and C2 with 78% accuracy (p<0.05). Speed discrimination was achieved with a Weber Fraction of 0.56 ± 0.09. CONCLUSIONS: Given the complexity of tactile experience and limitations of current neural interfaces, it was previously not thought possible to recreate intricate sensations. Nevertheless, we show that spatiotemporal ICMS can produce complex sensations with existing technology. This demonstrates the potential for neuroprosthetics to restore life-enhancing touch in people with paralysis or limb loss.