Ajemian R, Bullock D, Grossberg S
Department of Cognitive and Neural Systems and Center for Adaptive Systems, Boston University, Boston, Massachusetts 02215, USA.
J Neurophysiol. 2000 Nov;84(5):2191-203. doi: 10.1152/jn.2000.84.5.2191.
During goal-directed reaching in primates, a sensorimotor transformation generates a dynamical pattern of muscle activation. Within the context of this sensorimotor transformation, a fundamental question concerns the coordinate systems in which individual cells in the primary motor cortex (MI) encode movement direction. This article develops a mathematical framework that computes, as a function of the coordinate system in which an individual cell is hypothesized to operate, the spatial preferred direction (pd) of that cell as the arm configuration and hand location vary. Three coordinate systems are explicitly modeled: Cartesian spatial, shoulder-centered, and joint angle. The computed patterns of spatial pds are distinct for each of these three coordinate systems, and experimental approaches are described that can capitalize on these differences to compare the empirical adequacy of each coordinate hypothesis. One particular experiment involving curved motion was analyzed from this perspective. Out of the three coordinate systems tested, the assumption of joint angle coordinates best explained the observed cellular response properties. The mathematical framework developed in this paper can also be used to design new experiments that are capable of disambiguating between a given set of specified coordinate hypotheses.
在灵长类动物进行目标导向的伸手动作时，感觉运动转换会产生肌肉激活的动态模式。在这种感觉运动转换的背景下，一个基本问题涉及到初级运动皮层（MI）中单个细胞编码运动方向所采用的坐标系。本文开发了一个数学框架，该框架根据假设单个细胞所运行的坐标系，计算出随着手臂配置和手部位置的变化该细胞的空间偏好方向（pd）。明确建模了三种坐标系：笛卡尔空间坐标系、肩部中心坐标系和关节角度坐标系。对于这三种坐标系中的每一种，计算出的空间pd模式都是不同的，并且描述了一些实验方法，这些方法可以利用这些差异来比较每个坐标假设在经验上的充分性。从这个角度分析了一个涉及曲线运动的特定实验。在测试的三种坐标系中，关节角度坐标的假设最能解释观察到的细胞反应特性。本文开发的数学框架还可用于设计新的实验，这些实验能够区分给定的一组特定坐标假设。
