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Published August 2019 | Published
Journal Article Open

Functional Frequency Discrimination From Cortical Somatosensory Stimulation in Humans


Recently, efforts to produce artificial sensation through cortical stimulation of primary somatosensory cortex (PSC) in humans have proven safe and reliable. Changes in stimulation parameters like frequency and amplitude have been shown to elicit different percepts, but without clearly defined psychometric profiles. This study investigates the functionally useful limits of frequency changes on the percepts felt by three epilepsy patients with subdural electrocorticography (ECoG) grids. Subjects performing a hidden target task were stimulated with parameters of constant amplitude, pulse-width, and pulse-duration, and a randomly selected set of two frequencies (20, 30, 40, 50, 60, and 100 Hz). They were asked to decide which target had the "higher" frequency. Objectively, an increase in frequency differences was associated with an increase in perceived intensity. Reliable detection of stimulation occurred at and above 40 Hz with a lower limit of detection around 20 Hz and a just-noticeable difference estimated at less than 10 Hz. These findings suggest that frequency can be used as a reliable, adjustable parameter and may be useful in establishing settings and thresholds of functionality in future BCI systems.

Additional Information

© 2019 Kramer, Lamorie-Foote, Barbaro, Lee, Peng, Gogia, Liu, Kellis and Lee. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms. Received: 31 January 2019; Accepted: 25 July 2019; Published: 07 August 2019. This study was carried out in accordance with the recommendations of the University of Southern California Health Sciences Campus Institutional Review Board with written informed consent from all subjects. All subjects gave written informed consent in accordance with the Declaration of Helsinki. The protocol was approved by the University of Southern California Health Sciences Campus Institutional Review Board. Author Contributions: DK, BL, SK, and CL conceived the original ideas and experiments. BL and DK carried out the experiments. All authors interpreted the data, edited the manuscript, provided critical feedback, and helped to shape the research and analysis. DK, KL-F, CL, BK, and SK led the writing of the manuscript. We wish to acknowledge the generous support of Cal-BRAIN: A Neurotechnology Program for California, National Center for Advancing Translational Science (NCATS) of the U.S. National Institutes of Health (KL2TR001854), National Institutes of Health (R25 NS099008-01), the Neurosurgery Research and Education Foundation (NREF), the Tianqiao and Chrissy Chen Brain-Machine Interface Center at Caltech, the Boswell Foundation and the Della Martin Foundation, and the University of Southern California Neurorestoration Center. None of the listed sources of funding had a role in study design, collection, analysis, and interpretation of data, or writing of the manuscript. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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August 19, 2023
October 18, 2023