Neural mechanisms for control of reaching in the monkey parietal cortex

众所周知，顶叶皮层与空间感知有关。然而，最近对清醒猴子的神经生理学研究表明，顶叶皮层的神经元参与了伸手和操纵的控制。在这个项目中，我们首先通过将muscimol微量注射到顶棚内沟外侧的几个区域，确定了控制伸手和手部操作的负责区域，然后记录了这些区域的伸手神经元，以研究伸手的神经机制。我们将muscimol注射到两个区域：1)顶棚内沟外侧前区（Area AIP）， 2)顶棚内外侧区最前部（Area LIP）。在AIP区注射muscimol可造成严重的手部操作缺陷。在注射之前，猴子会调整手指的形状，以便拿起一小块食物，然而，注射后，猴子会伸出手指，直到它们碰到食物。注射muscimol到LIP区前部，导致手未到达，但手的预塑形没有任何缺陷。误差距离小；猴子试着一次又一次地捡起一小块食物，直到它碰到了指尖。这些结果似乎表明，伸手和手操作的神经控制机制在顶骨内沟侧壁的不同区域是分离的。在几乎相同的区域也发现了与到达运动相关的神经元。我们训练猴子进行手部操作任务和伸手任务。我们确定了64个神经元为到达神经元，因为这些神经元在任务的到达期被强烈激活。当猴子伸手到特定形状的物体时，这些神经元中有近60%优先被激活，然而，其余的神经元在猴子伸手时被激活。我们还根据活动的主要成分将到达神经元分为三种类型。在优先激活的到达神经元中，“视觉优势”型神经元的亲代明显高于非选择性激活的到达神经元。优先激活的到达神经元可能参与预成型运动而不是到达运动。我们测试了24个神经元在运动方向上的选择性，但大多数神经元（24个神经元中的19个）在运动方向上没有选择性。只有5个神经元在运动方向上有选择性，但它们的选择性并不那么明显。我们还研究了注视方向对一些神经元的影响，发现当猴子到达注视点时，大约一半的神经元（11个神经元中的5个）更加活跃。我们发现，当猴子安静地把手放在注视点上时，其他一些神经元在注视任务中非常活跃，但当手的视线被遮住时，它们就不活跃了。这些结果表明，该区域的这种类型的到达神经元可能在精细调节到达运动（如指向运动而不是弹道运动）中起关键作用。少

The parietal cortex is well known to be involved in perception of space. However, recent neurophysiological studies in awake monkeys indicated that neurons in the parietal cortex were involved in the control of reaching and manipulation. In this project, first we identified the responsible areas for control of reaching and hand manipulation by micro injection of muscimol into several areas of the lateral bank of intraparietal sulcus, then recorded reaching neurons in these areas to investigate the neural mechanisms of reaching.We injected muscimol into two areas : 1) Anterior part of the lateral bank of the intraparietal sulcus (Area AIP), 2) Most anterior part of lateral intraparietal area (area LIP). The injection of muscimol into area AIP caused sever deficit of hand manipulation. Before the injection the monkey preshaped its fingers to pick up a small piece of food, however, after the injection the monkey extended its finger until they touched the food. The injection of muscimol in … More to anterior part of area LIP caused miss-reaching without any deficits in preshaping of the hand. The distance of error was small ; the monkey tried to pick up a small piece of food again and again until it touched finger tip. These results seem to indicated that the neural control mechanisms for reaching and hand manipulation are segregated into different areas in the lateral bank of the intraparietal sulcus.Neurons related to reaching movements were also identified in almost same area. We trained the monkey to perform the hand manipulation task and the reaching task. We identified sixty four neurons as reaching neurons because these were activated vigorously during reaching period of the task. Almost 60% of these neurons were preferentially activated when the monkey reached to a particular shape of object, however, the rest were activated whenever the monkey reached out. We also classified the reaching neurons into three types by predominant component of activity. In preferentially activated reaching neurons, "visual dominant" type of neurons were significantly higher parentage than in non-selectively activated reaching neurons. Preferentially activated reaching neurons are likely involved in preshaping movement rather than reaching movement. We tested the selectivity in movement direction of 24 neurons, however, most of them (19 of 24) were not selective in movement direction. Only five neurons were selective in movement direction, however, their selectivity was not so sharp. We also investigated the effect of gaze direction in some neurons and found about half of them (5 of 11) were more active when the monkey reached toward the fixation point. We found some other neurons which were very active during the fixation task in which the monkey put its hand on the fixation point quietly but not active when the view of the hand was covered. These results suggest that this type of reaching neurons in this area may play a crucial role in fine adjustment of reaching movement such as pointing rather than ballistic movement. Less