Departments of1Neurosurgery and.
2Neurorestoration Center, and.
Neurosurg Focus. 2020 Feb 1;48(2):E2. doi: 10.3171/2019.11.FOCUS19696.
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.
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.
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.
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.
刺激初级躯体感觉皮层（S1）已成功地在人类和动物中诱发出人工躯体感觉，但对于产生强烈的躯体感觉知觉所需的最佳刺激参数仍知之甚少。在这项研究中，作者研究了频率作为闭环脑-机接口（BCI）系统中人工躯体感觉的可调刺激参数。
三名在手区有硬膜下微电极网格的癫痫患者被要求比较不同刺激频率引起的知觉。在所有试验中，幅度、脉冲宽度和持续时间保持不变。在每个试验中，受试者体验 2 次刺激，并报告他们认为哪一次刺激的频率更高。使用了两种范式：首先是 50 Hz 与 100 Hz 比较，以确定比较频率的有效性，然后是 2、5、10、20、50 或 100 Hz 的随机比较。
随着刺激频率的增加，受试者描述的感觉是“更强烈”或“更快”。总的来说，当比较 50 Hz 和 100 Hz 刺激时，参与者的准确率达到 98.0%。在第二个范式中，总体准确率为 73.3%。如果两个测试频率都小于或等于 10 Hz，则准确率为 41.7%，当一个频率大于 10 Hz 时准确率增加到 79.4%（p = 0.01）。当两个刺激频率都小于或等于 20 Hz 时，准确率为 40.7%，而当一个频率大于 20 Hz 时准确率为 91.7%（p < 0.001）。当刺激频率为 50 Hz 时，准确率为 85%。因此，检测下限出现在 20 Hz，当测试较低频率时，准确率显著下降。在测试 10 Hz 与 20 Hz 的试验中，准确率为 16.7%，而在测试 20 Hz 与 50 Hz 的试验中，准确率为 85.7%（p < 0.05）。在频率差异大于或等于 30 Hz 的情况下，准确率大于偶然水平。
大于 20 Hz 的频率可作为可调节参数，以产生可区分的感觉。这些发现可能有助于为未来的 BCI 系统提供设置和实现的自由度信息。
