Graczyk Emily L, Schiefer Matthew A, Saal Hannes P, Delhaye Benoit P, Bensmaia Sliman J, Tyler Dustin J
Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH 44106, USA.
Louis Stokes Cleveland Veterans Affairs Medical Center, Cleveland, OH 44106, USA.
Sci Transl Med. 2016 Oct 26;8(362):362ra142. doi: 10.1126/scitranslmed.aaf5187.
Electrical stimulation of sensory nerves is a powerful tool for studying neural coding because it can activate neural populations in ways that natural stimulation cannot. Electrical stimulation of the nerve has also been used to restore sensation to patients who have suffered the loss of a limb. We have used long-term implanted electrical interfaces to elucidate the neural basis of perceived intensity in the sense of touch. To this end, we assessed the sensory correlates of neural firing rate and neuronal population recruitment independently by varying two parameters of nerve stimulation: pulse frequency and pulse width. Specifically, two amputees, chronically implanted with peripheral nerve electrodes, performed each of three psychophysical tasks-intensity discrimination, magnitude scaling, and intensity matching-in response to electrical stimulation of their somatosensory nerves. We found that stimulation pulse width and pulse frequency had systematic, cooperative effects on perceived tactile intensity and that the artificial tactile sensations could be reliably matched to skin indentations on the intact limb. We identified a quantity we termed the activation charge rate (ACR), derived from stimulation parameters, that predicted the magnitude of artificial tactile percepts across all testing conditions. On the basis of principles of nerve fiber recruitment, the ACR represents the total population spike count in the activated neural population. Our findings support the hypothesis that population spike count drives the magnitude of tactile percepts and indicate that sensory magnitude can be manipulated systematically by varying a single stimulation quantity.
感觉神经的电刺激是研究神经编码的有力工具，因为它能够以自然刺激无法做到的方式激活神经群体。神经的电刺激也已被用于帮助肢体缺失患者恢复感觉。我们使用长期植入的电接口来阐明触觉中感知强度的神经基础。为此，我们通过改变神经刺激的两个参数：脉冲频率和脉冲宽度，分别评估了神经放电率和神经元群体募集的感觉相关性。具体而言，两名长期植入外周神经电极的截肢者，针对其体感神经的电刺激执行了三项心理物理学任务——强度辨别、量级估计和强度匹配。我们发现，刺激脉冲宽度和脉冲频率对感知到的触觉强度具有系统性的协同作用，并且人工触觉感受能够可靠地与完整肢体上的皮肤压痕相匹配。我们确定了一个从刺激参数得出的量，我们称之为激活电荷率（ACR），它能够预测所有测试条件下人工触觉感知的大小。基于神经纤维募集的原理，ACR代表了被激活神经群体中的总群体尖峰计数。我们的研究结果支持群体尖峰计数驱动触觉感知大小的假设，并表明可以通过改变单个刺激量来系统性地操纵感觉量级。
