He S Q, Dum R P, Strick P L
Department of Physiology, SUNY Health Science Center, Syracuse 13210, USA.
J Neurosci. 1995 May;15(5 Pt 1):3284-306. doi: 10.1523/JNEUROSCI.15-05-03284.1995.
We examined the topographic organization of corticospinal neurons in the four premotor areas on the medial wall of the hemisphere of macaques. These motor areas include the supplementary motor area (SMA) and three areas buried within the cingulate sulcus: the caudal cingulate motor area on the dorsal bank (CMAd), the caudal cingulate motor area on the ventral bank (CMAv), and the rostral cingulate motor area (CMAr). In one set of animals, we injected one fluorescent tracer into lower cervical segments of the spinal cord and another fluorescent tracer into lower lumbosacral segments to define the topographic organization of arm and leg representation within each premotor area. Similarly, in another set of animals, we injected different tracers into upper cervical and lower cervical segments to provide an indication of the topographic organization of proximal and distal arm representation within the arm representation of each premotor area. We found that all four of the premotor areas on the medial wall project to cervical and lumbosacral segments of the spinal cord. Three of these areas (SMA, CMAd, and CMAv) are like the primary motor cortex in having distinct arm and leg representations. The arm representation in each of the four motor areas on the medial wall contains separate regions that project densely to upper or to lower cervical segments. This observation suggests that each motor area contains distinct proximal and distal representations of the arm. Surprisingly, the size of the distal representation is comparable to or larger than the size of the proximal representation in each motor area. Thus, contrary to some previous hypotheses, the anatomical substrate exists for the premotor areas on the medial wall to be involved in the control of distal, as well as proximal arm movements. Our results provide a new map for guiding the exploration of the motor functions of the medial wall of the hemisphere. Furthermore, the observations of the present study support our suggestion that each of the premotor areas may be an important source of descending commands for the generation and control of movement.
我们研究了猕猴大脑半球内侧壁四个运动前区中皮质脊髓神经元的拓扑组织。这些运动区包括辅助运动区（SMA）以及扣带沟内的三个区域：背侧缘的尾侧扣带运动区（CMAd）、腹侧缘的尾侧扣带运动区（CMAv）和吻侧扣带运动区（CMAr）。在一组动物中，我们将一种荧光示踪剂注入脊髓颈下段，另一种荧光示踪剂注入腰骶下段，以确定每个运动前区内臂部和腿部代表区的拓扑组织。同样，在另一组动物中，我们将不同的示踪剂注入颈上段和颈下段，以显示每个运动前区内臂部代表区内近端和远端代表区的拓扑组织。我们发现，内侧壁上的所有四个运动前区都投射到脊髓的颈段和腰骶段。其中三个区域（SMA、CMAd和CMAv）与初级运动皮层相似，具有明显不同的臂部和腿部代表区。内侧壁上四个运动区中的每一个区的臂部代表区都包含分别密集投射到颈上段或颈下段的不同区域。这一观察结果表明，每个运动区都包含臂部不同的近端和远端代表区。令人惊讶的是，每个运动区内远端代表区的大小与近端代表区的大小相当或更大。因此，与之前的一些假设相反，内侧壁上的运动前区存在参与控制远端以及近端臂部运动的解剖学基础。我们的研究结果为指导探索大脑半球内侧壁的运动功能提供了一张新的图谱。此外，本研究的观察结果支持了我们的观点，即每个运动前区可能是运动产生和控制过程中下行指令的重要来源。
