Widener G L, Cheney P D
Department of Physiology and Smith Mental Retardation and Human Development Research Center, University of Kansas Medical Center, Kansas City 66160, USA.
J Neurophysiol. 1997 May;77(5):2446-65. doi: 10.1152/jn.1997.77.5.2446.
It is well known that electrical stimulation of primary somatosensory cortex (SI) evokes movements that resemble those evoked from primary motor cortex. These findings have led to the concept that SI may possess motor capabilities paralleling those of motor cortex and speculation that SI could function as a robust relay mediating motor responses from central and peripheral inputs. The purpose of this study was to rigorously examine the motor output capabilities of SI areas with the use of the techniques of spike- and stimulus-triggered averaging of electromyographic (EMG) activity in awake monkeys. Unit recordings were obtained from primary motor cortex and SI areas 3a, 3b, 1, and 2 in three rhesus monkeys. Spike-triggered averaging was used to assess the output linkage between individual cells and motoneurons of the recorded muscles. Cells in motor cortex producing postspike facilitation (PSpF) in spike-triggered averages of rectified EMG activity were designated corticomotoneuronal (CM) cells. Motor output efficacy was also assessed by applying stimuli through the microelectrode and computing stimulus-triggered averages of rectified EMG activity. One hundred seventy-one sites in motor cortex and 68 sites in SI were characterized functionally and tested for motor output effects on muscle activity. The incidence, character, and magnitude of motor output effects from SI areas were in sharp contrast to effects from CM cell sites in primary motor cortex. Of 68 SI cells tested with spike-triggered averaging, only one area 3a cell produced significant PSpF in spike-triggered averages of EMG activity. In comparison, 20 of 171 (12%) motor cortex cells tested produced significant postspike effects. Single-pulse intracortical microstimulation produced effects at all CM cell sites in motor cortex but at only 14% of SI sites. The large fraction of SI effects that was inhibitory represented yet another marked difference between CM cell sites in motor cortex and SI sites (25% vs 93%). The fact that motor output effects from SI were frequently absent or very weak and predominantly inhibitory emphasizes the differing motor capabilities of SI compared with primary motor cortex.
众所周知，对初级体感皮层（SI）进行电刺激会引发类似于从初级运动皮层引发的运动。这些发现导致了这样一种概念，即SI可能具有与运动皮层平行的运动能力，并且有人推测SI可以作为一个强大的中继站，介导来自中枢和外周输入的运动反应。本研究的目的是利用清醒猴子的肌电图（EMG）活动的尖峰触发和刺激触发平均技术，严格检查SI区域的运动输出能力。从三只恒河猴的初级运动皮层以及SI区域3a、3b、1和2获得了单位记录。尖峰触发平均法用于评估单个细胞与所记录肌肉的运动神经元之间的输出联系。在整流EMG活动的尖峰触发平均值中产生尖峰后易化（PSpF）的运动皮层细胞被指定为皮质运动神经元（CM）细胞。还通过微电极施加刺激并计算整流EMG活动的刺激触发平均值来评估运动输出效能。对运动皮层中的171个位点和SI中的68个位点进行了功能表征，并测试了其对肌肉活动的运动输出影响。SI区域的运动输出影响的发生率、特征和大小与初级运动皮层中CM细胞位点的影响形成鲜明对比。在用尖峰触发平均法测试的68个SI细胞中，只有一个3a区域的细胞在EMG活动的尖峰触发平均值中产生了显著的PSpF。相比之下，在测试的171个（12%）运动皮层细胞中，有20个产生了显著的尖峰后效应。单脉冲皮质内微刺激在运动皮层的所有CM细胞位点都产生了效应，但在SI位点中只有14%产生了效应。SI效应中很大一部分是抑制性的，这代表了运动皮层中的CM细胞位点与SI位点之间的另一个显著差异（25%对93%）。SI的运动输出效应经常不存在或非常微弱且主要是抑制性的，这一事实强调了SI与初级运动皮层相比具有不同的运动能力。
