The goal of this study is to identify the cortical area maximally active over the primary sensorimotor cortex (SM1) and characterize the cortical encoding for force production by wrist muscles in the human brain. The technique of functional near-infrared spectroscopy (fNIRS) was used to continuously monitor the changes in hemoglobin concentrations from the left hemisphere during isometric contractions of wrist flexion muscles over a broad range of load forces (0 ∼ 8 kgf) on the right hand. As previously shown in primate studies, this action produced hemodynamic activity predominantly in the wrist area localized dorsally to the finger region over SM1 and the hemodynamic response was systematically related to the level of load intensity. The coding scheme for force production in terms of hemodynamic signals was characterized defining eight trajectory parameters (four for amplitude coding and four for temporal coding) and analyzed for the area maximally activated over SM1. The trajectory parameter representing the oxygenated hemoglobin concentration change at the end of motor task (amplitude coding) and the timing of maximum change in oxygenated hemoglobin concentration (temporal coding) was most strongly correlated with the load variation in a superliner manner. All these results indicate the applicability of fNIRS to monitor and decode cortical activity that is correlated with low-level motor control such as isometric muscle contractions. This study may provide not only insights into cortical neural control of muscle force but also predictors of muscle force in clinical diagnostics and neural interfaces for the human brain.

本研究的目的是确定初级感觉运动皮层 (SM1) 上最活跃的皮层区域，并表征人类大脑中腕部肌肉产生力的皮层编码。功能性近红外光谱 (fNIRS) 技术用于连续监测在右手手腕屈曲肌肉在宽范围负载力 (0 ~ 8 kgf) 下等长收缩期间左半球血红蛋白浓度的变化。正如先前在灵长类动物研究中所显示的那样，该动作主要在位于 SM1 上手指区域背侧的腕部区域产生血流动力学活动，并且血流动力学响应与负荷强度水平系统相关。根据血液动力学信号产生力的编码方案的特征在于定义了八个轨迹参数（四个用于幅度编码，四个用于时间编码）并分析了 SM1 上最大激活的区域。代表运动任务结束时氧合血红蛋白浓度变化（幅度编码）和氧合血红蛋白浓度最大变化时间（时间编码）的轨迹参数与超线性方式的负荷变化最密切相关。所有这些结果表明 fNIRS 适用于监测和解码与低水平运动控制（如等长肌肉收缩）相关的皮层活动。