Multi-channel intra-cortical micro-stimulation yields quick reaction times and evokes natural somatosensations in a human participant

Somatosensory brain-machine-interfaces (BMIs) can create naturalistic sensations by modulating activity of neural populations in the brain. By utilizing different spatial or temporal patterns of intra-cortical micro-stimulation (ICMS) in primary sensory cortex (S1), human patients suffering somatosensory loss can experience both cutaneous and proprioceptive sensory feedback. As evidenced by motor deficits in deafferented patients, rapid somatosensory feedback is critical for dexterous motor ability, in part because visual feedback is much slower than naturally occurring somatosensory input. However, somatosensory BMI studies typically report significantly longer cognitive processing latencies for cortical electrical stimulation than for naturally occurring somatosensations or visual sensations. In this study, we show that multi-channel electrical stimulation patterns elicit naturalistic somatosensory percepts in a human tetraplegic participant. Crucially, somatosensations evoked by multi-channel ICMS are cognitively processed at comparable latencies to naturally evoked sensations and significantly faster than visual sensations, as measured via a simple reaction time test. Further investigation demonstrated multi-channel stimulation could significantly reduce minimum amplitude detection thresholds and such reductions in charge density resulted in more frequent “natural” sensation descriptors reported by the human participant. Multi-channel ICMS patterns also evoked percepts with highly stable somatotopic locations. While some single-channel ICMS patterns evoked sensations 20-80% of the time, most multi-channel patterns could evoke sensations with 100% repeatability, an important step in demonstrating BCI device reliability. These improvements are all significant advances towards state-of-the-art sensory BMIs. The addition of such low-latency artificial sensory feedback to motor BMIs is expected to improve movement accuracy and increase embodiment for human users. ### Competing Interest Statement The authors have declared no competing interest. ### Clinical Trial NCT01964261 ### Funding Statement Boswell Foundation T&C Chen Brain-machine Interface Center NIH/NINDS Grant U01NS098975 NIH/NINDS Grant U01NS123127 Craig F. Neilson Foundation ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: All human subject research, experimental design and biomedical devices used in this study were approved by the Institutional Review Boards (IRB) of the California Institute of Technology, University of Southern California, and Rancho Los Amigos National Rehabilitation Hospital for collection of this data. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes All data produced in the present study are available upon reasonable request to the authors