Kakei Shinji, Hoffman Donna S, Strick Peter L
Systems Neuroscience, Graduate School of Life Science, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
Neurosci Res. 2003 May;46(1):1-10. doi: 10.1016/s0168-0102(03)00031-2.
A central problem in motor research has been to understand how sensory signals are transformed to generate a goal-directed movement. This problem has been formulated as a set of coordinate transformations that begins with an extrinsic coordinate frame representing the spatial location of a target and ends with an intrinsic coordinate frame describing muscle activation patterns. Insight into this process of sensorimotor transformation can be gained by examining the coordinate frames of neuronal activity in interconnected regions of the brain. We recorded the activity of neurons in primary motor cortex (M1) and ventral premotor cortex (PMv) in a monkey trained to perform a task which dissociates three major coordinate frames of wrist movement: muscle, wrist joint, and an extrinsic coordinate frame. We found three major types of neurons in M1 and PMv. The first type was termed 'extrinsic-like'. The activity of these neurons appeared to encode the direction of movement in space independent of the patterns of wrist muscle activity or joint movement that produced the movements. The second type was termed 'extrinsic-like with gain modulation'. The activity of these neurons appeared to encode the direction of movement in space, but the magnitude (gain) of neuronal activity depended on the posture of the forearm. The third type was termed 'muscle-like' since their activity co-varied with muscle activity. The great majority of the directionally-tuned neurons in the PMv were classified as 'extrinsic-like' (48/59, 81%). A smaller group was classified as 'extrinsic-like with gain modulation' (7/59, 12%). In M1, the three types of neurons were more equally represented. Our results raise the possibility that cortical processing between M1 and PMv may contribute to a sensorimotor transformation between extrinsic and intrinsic coordinate frames. Recent modeling studies have demonstrated the computational plausibility of such a process.
运动研究中的一个核心问题一直是理解感觉信号如何被转换以产生目标导向的运动。这个问题已被表述为一组坐标变换，它始于表示目标空间位置的外在坐标框架，终于描述肌肉激活模式的内在坐标框架。通过检查大脑相互连接区域中神经元活动的坐标框架，可以深入了解这种感觉运动转换过程。我们记录了一只经过训练执行一项任务的猴子的初级运动皮层（M1）和腹侧运动前皮层（PMv）中神经元的活动，该任务区分了手腕运动的三个主要坐标框架：肌肉、腕关节和外在坐标框架。我们在M1和PMv中发现了三种主要类型的神经元。第一种类型被称为“类外在型”。这些神经元的活动似乎编码了空间中的运动方向，而与产生运动的手腕肌肉活动模式或关节运动无关。第二种类型被称为“具有增益调制的类外在型”。这些神经元的活动似乎也编码了空间中的运动方向，但神经元活动的幅度（增益）取决于前臂的姿势。第三种类型被称为“类肌肉型”，因为它们的活动与肌肉活动共同变化。PMv中绝大多数方向调谐神经元被归类为“类外在型”（48/59，81%）。一小部分被归类为“具有增益调制的类外在型”（7/59，12%）。在M1中，这三种类型的神经元分布更为均衡。我们的结果提出了一种可能性，即M1和PMv之间的皮层处理可能有助于外在和内在坐标框架之间的感觉运动转换。最近的建模研究已经证明了这一过程在计算上的合理性。
