Intracortical Somatosensory Stimulation to Elicit Fingertip Sensations in an Individual With Spinal Cord Injury

Abstract

Background and Objectives:The restoration of touch to fingers and fingertips is critical to achieving dexterous neuroprosthetic control for individuals with sensorimotor dysfunction. However, localized fingertip sensations have not been evoked via intracortical microstimulation (ICMS).Methods:Using a novel intraoperative mapping approach, we implanted electrode arrays in the finger areas of left and right somatosensory cortex and delivered ICMS over a 2-year period in a human participant with spinal cord injury.Results:Stimulation evoked tactile sensations in 8 fingers, including fingertips, spanning both hands. Evoked percepts followed expected somatotopic arrangements. The subject was able to reliably identify up to 7 finger-specific sites spanning both hands in a finger discrimination task. The size of the evoked percepts was on average 33% larger than a fingerpad, as assessed via manual markings of a hand image. The size of the evoked percepts increased modestly with increased stimulation intensity, growing 21% as pulse amplitude increased from 20µA to 80µA. Detection thresholds were estimated on a subset of electrodes, with estimates of 9.2-35µA observed, roughly consistent with prior studies.Discussion:These results suggest that ICMS can enable the delivery of consistent and localized fingertip sensations during object manipulation by neuroprostheses for individuals with somatosensory deficits.Clinical Trial Information:This study is registered on ClinicalTrials.gov with identifier NCT03161067.

Perceived Timing of Cutaneous Vibration and Intracortical Microstimulation of Human Somatosensory Cortex

“…The goal of this study was to evaluate the relative latency at which intensity-matched artificial and natural touch sensations are perceived. To this end, we conducted reaction time tests and TOJ tests with a human participant implanted with stimulating microelectrodes in his somatosensory cortex [4], [20]. Consistent with previous studies [10]- [12], we found that the reaction time to vibratory stimuli was 48-90 ms faster than artificial tactile percepts elicited by cortical stimulation, even when the two stimuli were matched in perceived intensity.…”

“…Intracortical microstimulation of somatosensory cortex to elicit tactile percepts in the hand This study involved a human participant who was chronically implanted with microelectrode arrays in the bilateral primary motor cortices and area 1 of the somatosensory cortices (see Fig 1a, and McMullen et al and Fifer et al for additional details on these implants [4], [20]). In the present study, only the stimulating electrodes implanted in somatosensory cortex were used.…”

“…This study involved a human participant who was chronically implanted with microelectrode arrays in the bilateral primary motor cortices and area 1 of the [4], [20]). In the present study, only the stimulating electrodes implanted in somatosensory cortex were used.…”

“…The copyright holder for this this version posted December 31, 2021. ; https://doi.org/10.1101/2021.12.28.21268447 doi: medRxiv preprint verbally report the regions of the hand in which he felt a tactile percept. These electrode mappings are more thoroughly discussed in Fifer et al [4].…”

“…Manual touch plays a critical role in object manipulation and performing activities of daily living [1]. One approach to restoring touch to individuals with somatosensory deficits is electrical activation of neurons in the hand representation of somatosensory cortex [2]- [4]. These artificial tactile signals can be used to support and enhance the use of a prosthetic hand [5].…”