Kurata Kiyoshi, Hoshi Eiji
Department of Physiology, Hirosaki University School of Medicine, Hirosaki 036-8562, Sendai 980-8575 Japan.
J Neurophysiol. 2002 Dec;88(6):3118-32. doi: 10.1152/jn.00070.2002.
We examined how the transformation of coordinates from visual to motor space is reflected by neuronal activity in the ventral premotor cortex (PMv) of monkeys. Three monkeys were trained to reach with their right hand for a target that appeared on a screen. While performing the task, the monkeys wore prisms that shifted the image of the target 10 degrees, left or right, or wore no prisms, for a block of 200 trials. The nine targets were located in the same positions in visual space regardless of whether the prisms were present. Wearing the prisms required the monkeys to initiate a movement in a direction that was different from the apparent target location. Thus using the prisms, we could dissociate visual space from motor space. While the monkey performed the behavioral task, we recorded neuronal activity in the left PMv and primary motor cortex (MI), and various kinds of task-related neuronal activity were found in the motor areas. These included neurons that changed their activity during a reaction time (RT) period (the period between target presentation and movement onset), which were called "movement-related neurons" and selected for analysis. In these neurons, activity during a movement time (MT) period was also compared. Using general linear models for our statistical analysis, the neurons were then classified into four types: those whose activity was consistently dependent on location of targets in the visual coordinates regardless of whether the prisms were present or absent (V type); those that were consistently dependent on target location in the motor coordinates only; those that had different activity for both of the motor and visual coordinates; and those that had nondifferential activity for the two types of coordinates. The proportion of the four types of the neurons differed significantly between the PMv and MI. Most remarkably, neurons with V-type activity were almost exclusively recorded in the PMv and were almost exclusively found during the RT period. Such activity was never observed in an electromyogram of the working forelimb. Based on these observations, we postulate that the V and other types may represent the various intermediate stages of the transformation of coordinates and that the PMv plays a crucial role in transforming coordinates from visual to motor space.
我们研究了猴子腹侧运动前区（PMv）的神经元活动是如何反映从视觉空间到运动空间的坐标转换的。三只猴子经过训练，用右手去够屏幕上出现的目标。在执行任务时，猴子佩戴棱镜，使目标图像向左或向右偏移10度，或者不佩戴棱镜，每种情况进行200次试验。无论是否佩戴棱镜，九个目标在视觉空间中的位置相同。佩戴棱镜要求猴子朝着与目标明显位置不同的方向发起运动。因此，通过使用棱镜，我们可以将视觉空间与运动空间区分开来。当猴子执行行为任务时，我们记录了左侧PMv和初级运动皮层（MI）的神经元活动，并在运动区域发现了各种与任务相关的神经元活动。其中包括在反应时间（RT）（从目标呈现到运动开始的时间段）内改变其活动的神经元，这些神经元被称为“运动相关神经元”并被选作分析对象。在这些神经元中，还比较了运动时间（MT）内的活动。然后，我们使用一般线性模型进行统计分析，将这些神经元分为四种类型：无论是否佩戴棱镜，其活动始终依赖于视觉坐标中目标位置的神经元（V型）；仅始终依赖于运动坐标中目标位置的神经元；对运动和视觉坐标都有不同活动的神经元；以及对两种坐标没有差异活动的神经元。这四种类型的神经元在PMv和MI之间的比例有显著差异。最值得注意的是，具有V型活动的神经元几乎只在PMv中记录到，并且几乎只在RT期间出现。在前肢工作的肌电图中从未观察到这种活动。基于这些观察结果，我们推测V型和其他类型可能代表坐标转换的各个中间阶段，并且PMv在将坐标从视觉空间转换到运动空间中起着关键作用。
