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Published February 2020 | Published
Journal Article Open

Utility and lower limits of frequency detection in surface electrode stimulation for somatosensory brain-computer interface in humans


Objective: Stimulation of the primary somatosensory cortex (S1) has been successful in evoking artificial somatosensation in both humans and animals, but much is unknown about the optimal stimulation parameters needed to generate robust percepts of somatosensation. In this study, the authors investigated frequency as an adjustable stimulation parameter for artificial somatosensation in a closed-loop brain-computer interface (BCI) system. Methods: Three epilepsy patients with subdural mini-electrocorticography grids over the hand area of S1 were asked to compare the percepts elicited with different stimulation frequencies. Amplitude, pulse width, and duration were held constant across all trials. In each trial, subjects experienced 2 stimuli and reported which they thought was given at a higher stimulation frequency. Two paradigms were used: first, 50 versus 100 Hz to establish the utility of comparing frequencies, and then 2, 5, 10, 20, 50, or 100 Hz were pseudorandomly compared. Results: As the magnitude of the stimulation frequency was increased, subjects described percepts that were "more intense" or "faster." Cumulatively, the participants achieved 98.0% accuracy when comparing stimulation at 50 and 100 Hz. In the second paradigm, the corresponding overall accuracy was 73.3%. If both tested frequencies were less than or equal to 10 Hz, accuracy was 41.7% and increased to 79.4% when one frequency was greater than 10 Hz (p = 0.01). When both stimulation frequencies were 20 Hz or less, accuracy was 40.7% compared with 91.7% when one frequency was greater than 20 Hz (p < 0.001). Accuracy was 85% in trials in which 50 Hz was the higher stimulation frequency. Therefore, the lower limit of detection occurred at 20 Hz, and accuracy decreased significantly when lower frequencies were tested. In trials testing 10 Hz versus 20 Hz, accuracy was 16.7% compared with 85.7% in trials testing 20 Hz versus 50 Hz (p < 0.05). Accuracy was greater than chance at frequency differences greater than or equal to 30 Hz. Conclusions: Frequencies greater than 20 Hz may be used as an adjustable parameter to elicit distinguishable percepts. These findings may be useful in informing the settings and the degrees of freedom achievable in future BCI systems.

Additional Information

© 2020 American Association of Neurological Surgeons. SUBMITTED September 14, 2019. ACCEPTED November 4, 2019. This study was funded by a grant awarded to D.R.K. through the National Institutes of Health (grant no. R25 NS099008-01). This study was also supported by Cal-BRAIN: A Neurotechnology Program for California, National Center for Advancing Translational Science (NCATS) of the National Institutes of Health (grant no. KL2TR001854), 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. The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper. Author Contributions: Conception and design: Kramer, Liu, Kellis, Lee. Acquisition of data: Kramer. Analysis and interpretation of data: Kramer, Lamorie-Foote. Drafting the article: Kramer, Lamorie-Foote. Critically revising the article: all authors. Reviewed submitted version of manuscript: all authors. Statistical analysis: all authors. Study supervision: Kramer, Nune, Liu, Kellis, Lee. Supplemental Information: Previous Presentations: Portions of this work were presented in abstract form at the 2016 North American Neuromodulation Society Meeting, Baltimore, Maryland, June 25–29, 2016.

Attached Files

Published - _10920684_-_Neurosurgical_Focus__Utility_and_lower_limits_of_frequency_detection_in_surface_electrode_stimulation_for_somatosensory_brain-computer_interface_in_humans.pdf



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August 22, 2023
October 19, 2023