Lo Yu Tung, Maggi Alessandro, Wu Kevin, Zhong Hui, Choi Wooseong, Nguyen Thanh Dat, Abedi Aidin, Agyeman Kofi, Sakellaridi Sofia, Reggie Edgerton Victor, Kreydin Evgeniy, Lee Darrin, Sideris Constantine, Liu Charles Y, Christopoulos Vassilios N
IEEE Trans Neural Syst Rehabil Eng. 2025;33:2004-2012. doi: 10.1109/TNSRE.2025.3570324.
Spinal cord injury (SCI) patients experience long-term deficits in motor and sensory functions. While brain-machine interface (BMI) has shown great promise for restoring neurological functions after SCI, spinal cord-machine interface (SCMI) offers unique advantages, such as more defined somatotopy and the compact organization of neural elements in the spinal cord. In the current study, we aim to demonstrate the feasibility of sensing and evoking compound action potentials (CAPs) via electrode implantation in spinal cord axonal bundles, an essential prerequisite for advancing SCMI development. To do so, we designed microelectrode arrays (MEA) optimized for recording and stimulation in the spinal cord. For sensory mapping, the MEAs were inserted into the lumbar dorsal column (i.e., the fasciculus gracilis) to determine somatotopic representations corresponding to tactile stimulation across lower body regions and assess proprioceptive signals with varying hip positions. For stimulations, at the L3 level, we delivered electrical pulses both rostrally, along ascending afferent tracts (dorsal column), and caudally, down descending corticospinal tract. We successfully captured axonal CAPs from the dorsal columns with high spatial precision that corresponded to known dermatomal somatotopy. Proprioceptive changes produced by abduction at the hip resulted in modulation of discharge frequency in the dorsal column axons. We demonstrated that stimulation pulses emitted by a caudally placed electrode could be propagated up the ascending fibers and be intercepted by a rostrally placed electrode array along the same axonal tracts. We also confirmed that electrical pulses can be directed down descending corticospinal tracts resulting in specific activations of lower limb muscles. These findings set a critical groundwork for developing closed-loop, bidirectional SCMI systems capable of sensing and modulating spinal cord activity.
脊髓损伤（SCI）患者会出现运动和感觉功能的长期缺陷。虽然脑机接口（BMI）在脊髓损伤后恢复神经功能方面显示出巨大潜力，但脊髓机接口（SCMI）具有独特优势，例如更明确的躯体定位以及脊髓中神经元件的紧凑组织。在当前研究中，我们旨在通过将电极植入脊髓轴突束来证明感知和诱发复合动作电位（CAPs）的可行性，这是推进SCMI发展的一个重要前提条件。为此，我们设计了针对脊髓记录和刺激进行优化的微电极阵列（MEA）。对于感觉映射，将MEA插入腰髓背柱（即薄束），以确定与下半身区域触觉刺激相对应的躯体定位表征，并评估不同髋关节位置时的本体感觉信号。对于刺激，在L3水平，我们沿上升的传入束（背柱）向头端以及沿下行的皮质脊髓束向尾端发送电脉冲。我们成功地以高空间精度从背柱捕获了与已知皮节躯体定位相对应的轴突CAPs。髋关节外展产生的本体感觉变化导致背柱轴突放电频率的调制。我们证明，由尾端放置的电极发出的刺激脉冲可以沿上升纤维向上传播，并被沿相同轴突束头端放置的电极阵列拦截。我们还证实，电脉冲可以沿下行的皮质脊髓束向下传导，从而导致下肢肌肉的特定激活。这些发现为开发能够感知和调节脊髓活动的闭环、双向SCMI系统奠定了关键基础。
