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J Neural Eng. 2019 Nov 28. doi: 10.1088/1741-2552/ab5cf3. [Epub ahead of print]

Short reaction times in response to multi-electrode intracortical microstimulation may provide a basis for rapid movement-related feedback.

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Biomedical Engineering, Northwestern University, 303 E Chicago Ave, Ward 5-198, Chicago, Illinois, 60611, UNITED STATES.
Physiology, Northwestern University Feinberg School of Medicine, Chicago, Illinois, UNITED STATES.



Tetraplegic patients using brain-machine interfaces (BMIs) can make visually guided reaches with robotic arms. However, restoring proprioceptive feedback to these patients will be critical, as evidenced by the movement deficiencies in patients with proprioceptive loss. Proprioception is critical in large part because it provides faster feedback than vision. Intracortical microstimulation (ICMS) is a promising approach, but the ICMS-evoked reaction time (RT) is typically slower than that to natural proprioceptive and often even visual cues, implying that ICMS feedback may not be fast enough to guide movement.


For most sensory modalities, RT decreases with increased stimulus intensity. Thus, it may be that stimulation intensities beyond what has previously been used will result in faster RTs. To test this, we compared the RT to ICMS applied through multi-electrode arrays in area 2 of somatosensory cortex to that of mechanical and visual cues.


We found that the RT to single-electrode ICMS decreased with increased current, frequency, and train length. For 100 μA, 330 Hz stimulation, the highest single-electrode intensity we tested routinely, most electrodes resulted in RTs slower than the mechanical cue but slightly faster than the visual cue. While increasing the current beyond 100 μA resulted in faster RTs, sustained stimulation at this level may damage tissue. Alternatively, by stimulating through multiple electrodes (mICMS), a large amount of current can be injected while keeping that through each electrode at a safe level. We found that stimulation with at least 480 μA equally distributed over 16 electrodes could produce RTs as much as 20 ms faster than the mechanical cue, roughly the conduction delay to cortex from the periphery.


These results suggest that mICMS may provide a means to supply rapid, movement-related feedback. Future neuroprosthetics may need spatiotemporally patterned mICMS to convey useful somatosensory information.


brain-machine interface; intracortical microstimulation; microelectrode array; somatosensory sensory feedback


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