Debowy D J, Ghosh S, Ro J Y, Gardner E P
Department of Physiology and Neuroscience, New York University School of Medicine, 550 First Avenue, MSB 442, New York, NY 10016, USA.
Exp Brain Res. 2001 Apr;137(3-4):269-91. doi: 10.1007/s002210000660.
To evaluate their functional roles during prehension, single-unit recordings were made in the hand area of primary somatosensory areas 3b, 1 and 2 (S-I) and posterior parietal areas 5 and 7 (PPC) of the same animal. Response profiles of mean firing rate during performance of a multistage reach, grasp, and lift task were analyzed to determine the period(s) of peak firing and to measure statistically significant rises or falls in rate compared with baseline. We used the peak firing stage(s) to subdivide the population into classes tuned to single actions or two successive stages, or into multiaction groups that had sustained facilitation (BT) or inhibition (GI) during hand-object interactions. Four times as many neurons fired at peak rates during acquisition stages (approach, contact, grasp) than upon release, and their firing rates were higher. Grasping evoked the strongest responses, as grasp-tuned neurons had the highest peak rates in the population; BT, contact-grasp, and grasp-lift cells also fired maximally in the grasp stage. Grasping also coincided with maximal inhibition of GI cells, as well as of neurons tuned to approach or relaxation of grasp. Holding evoked the lowest mean rates, and had the fewest tuned cells. S-I and PPC showed significant differences in behaviors evoking peak firing as well as facilitation and inhibition; these correlated with input modalities in each area. Hand contact with the object and positioning of the fingers for grasp was the most strongly represented behavior in anterior S-I, where 61% received tactile inputs from glabrous skin. Nearly 60% were facilitated at contact, 38% fired at peak rates, and 10% were inhibited; release of grasp evoked peak firing in only 5% of 3b-1 neurons. In posterior S-I, where proportions of tactile and deep inputs were similar, positioning and grasping elicited peak responses in 38% and 31%, respectively; 80% were facilitated or inhibited during grasping. During lift and hold, inhibition rose to 43%, while excitation declined under 10%. PPC had the highest proportions firing at peak rates during hand preshaping before contact (28%) and had the most facilitated responses (38%) in this stage. Only 10% fired at peak rates during grasping. During later manipulatory actions, proportions of facilitated and inhibited responses in PPC were similar to those in posterior S-I. The data support models in which PPC plans hand movements during prehension rather than guiding their execution. Sensory monitoring of hand-object interaction occurs in S-I, where cells sense specific hand behaviors, signal stage completion, enable error correction, and may update grasp programs formulated in PPC. The results are discussed in relation to those obtained from lesion studies in humans.
为了评估它们在抓握过程中的功能作用，在同一只动物的初级躯体感觉区3b、1和2（S-I）的手部区域以及顶叶后区5和7（PPC）进行了单单位记录。分析了在多阶段伸手、抓握和提起任务执行过程中平均放电率的反应曲线，以确定峰值放电期，并测量与基线相比放电率在统计学上的显著上升或下降。我们使用峰值放电阶段将神经元群体细分为针对单个动作或两个连续阶段进行调谐的类别，或细分为在手部与物体相互作用期间具有持续易化（BT）或抑制（GI）的多动作组。在获取阶段（接近、接触、抓握）以峰值速率放电的神经元数量是释放时的四倍，并且它们的放电率更高。抓握引发最强的反应，因为针对抓握进行调谐的神经元在群体中具有最高的峰值速率；BT、接触-抓握和抓握-提起细胞在抓握阶段也最大程度地放电。抓握还与GI细胞以及针对接近或抓握放松进行调谐的神经元的最大抑制同时发生。握持引发的平均放电率最低，并且调谐细胞最少。S-I和PPC在引发峰值放电以及易化和抑制的行为方面表现出显著差异；这些差异与每个区域的输入模式相关。手部与物体的接触以及手指抓握的定位在前S-I中是最强烈代表的行为，其中61%的神经元接收来自无毛皮肤的触觉输入。近60%的神经元在接触时易化，38%的神经元以峰值速率放电，10%的神经元受到抑制；抓握的释放仅在3b-1神经元的5%中引发峰值放电。在后S-I中，触觉和深部输入的比例相似，定位和抓握分别在38%和31%的神经元中引发峰值反应；80%的神经元在抓握期间易化或受到抑制。在提起和握持期间，抑制率上升至43%，而兴奋率下降至10%以下。PPC在接触前手部预塑形期间以峰值速率放电的比例最高（28%），并且在该阶段具有最多的易化反应（38%）。在抓握期间只有10%的神经元以峰值速率放电。在后期的操作动作中，PPC中易化和抑制反应的比例与后S-I中的相似。这些数据支持了这样的模型，即PPC在抓握过程中规划手部动作而不是指导其执行。手部与物体相互作用的感觉监测发生在S-I中，其中细胞感知特定的手部行为，发出阶段完成信号，实现错误纠正，并可能更新在PPC中制定的抓握程序。将结合从人类病变研究中获得的结果对这些结果进行讨论。
