He S Q, Dum R P, Strick P L
Research Service, Veterans Affairs Medical Center, Syracuse, New York 13210.
J Neurosci. 1993 Mar;13(3):952-80. doi: 10.1523/JNEUROSCI.13-03-00952.1993.
We examined the topographic organization of corticospinal neurons in the primary motor cortex and in the two premotor areas on the lateral surface of the hemisphere [i.e., the dorsal premotor area (PMd) and the ventral premotor area (PMv)]. In two macaques, we labeled corticospinal neurons that project beyond T7 or S2 by placing crystals of HRP into the dorsolateral funiculus at these segmental levels. In another seven macaques, we labeled corticospinal neurons that project to specific segmental levels of the spinal cord by injecting the fluorescent tracers fast blue and diamidino yellow into the gray matter of the cervical and lumbosacral segments. In one set of experiments (n = 2), we defined the representations of the arm and leg in each cortical motor area by injecting one of the two fluorescent tracers into lower cervical segments (C7-T1) and the other fluorescent tracer into lower lumbosacral segments (L6-S1) of the same animal. In another set of experiments (n = 5), we defined the representations of distal and proximal parts of the forelimb in each cortical motor area by injecting one of the two fluorescent tracers into lower cervical segments (C7-T1) and the other tracer into upper cervical segments (C2-C4) of the same animal. In the primary motor cortex and the PMd, cortical regions that project to lower cervical segments were largely separate from those that project to lower lumbosacral segments. In the PMv, few neurons were labeled after tracer injections into lower cervical segments or lower lumbosacral segments. However, corticospinal neurons were labeled in the PMv after tracer injections into upper cervical segments and after HRP placement in the dorsolateral funiculus at T7. The region of the PMv that projects to upper cervical segments was separate from that which projects below T7. Cortical regions that project to upper and lower cervical segments of the spinal cord overlapped considerably in the primary motor cortex and in the PMd. Despite this overlap, we found that the regions of the primary motor cortex and PMd that project most densely to upper cervical segments were largely separate from those that project most densely to lower cervical segments. Furthermore, we found two separate regions within area 4 that send corticospinal projections primarily to the lower cervical segments. One of these regions was located within the classical "hand" area of the primary motor cortex. The other was located at the medial edge of arm representation in the primary motor cortex.(ABSTRACT TRUNCATED AT 400 WORDS)
我们研究了初级运动皮层以及半球外侧表面的两个运动前区[即背侧运动前区（PMd）和腹侧运动前区（PMv）]中皮质脊髓神经元的拓扑组织。在两只猕猴中，我们通过将HRP晶体置于T7或S2节段水平的背外侧索，标记了投射至T7或S2节段以上的皮质脊髓神经元。在另外七只猕猴中，我们通过将荧光示踪剂快蓝和双脒基黄注入颈段和腰骶段的灰质，标记了投射至脊髓特定节段水平的皮质脊髓神经元。在一组实验（n = 2）中，我们通过将两种荧光示踪剂之一注入同一只动物的下颈段（C7 - T1），另一种荧光示踪剂注入下腰骶段（L6 - S1），来确定每个皮质运动区中手臂和腿部代表区。在另一组实验（n = 5）中，我们通过将两种荧光示踪剂之一注入同一只动物的下颈段（C7 - T1），另一种示踪剂注入上颈段（C2 - C4），来确定每个皮质运动区中前肢远端和近端部分的代表区。在初级运动皮层和PMd中，投射至下颈段的皮质区域与投射至下腰骶段的区域在很大程度上是分开的。在PMv中，向下颈段或下腰骶段注射示踪剂后，很少有神经元被标记。然而，向上颈段注射示踪剂以及将HRP置于T7节段的背外侧索后，PMv中的皮质脊髓神经元被标记。PMv中投射至上颈段的区域与投射至T7以下的区域是分开的。投射至脊髓上颈段和下颈段的皮质区域在初级运动皮层和PMd中存在相当程度的重叠。尽管存在这种重叠，我们发现初级运动皮层和PMd中最密集地投射至上颈段的区域与最密集地投射至下颈段的区域在很大程度上是分开的。此外，我们在4区发现了两个分开的区域，它们主要将皮质脊髓投射发送至下颈段。其中一个区域位于初级运动皮层的经典 “手部” 区域内。另一个位于初级运动皮层中手臂代表区的内侧边缘。（摘要截断于400字）
