Dum R P, Strick P L
Research Service, Veterans Administration Medical Center, Syracuse, New York 13210.
J Neurosci. 1991 Mar;11(3):667-89. doi: 10.1523/JNEUROSCI.11-03-00667.1991.
We determined the origin of corticospinal neurons in the frontal lobe. These neurons were labeled by retrograde transport of tracers after injections into either the dorsolateral funiculus at the second cervical segment or the gray matter of the spinal cord throughout the cervical enlargement. Using retrograde transport of tracer from the arm area of the primary motor cortex, we defined the arm representation in each premotor area in another set of animals. We found that corticospinal projections to cervical segments of the spinal cord originate from the primary motor cortex and from the 6 premotor areas in the frontal lobe. These are the same premotor areas that project directly to the arm area of the primary motor cortex. The premotor areas are located in parts of cytoarchitectonic area 6 on the lateral surface and medial wall of the hemisphere, as well as in subfields of areas 23 and 24 in the cingulate sulcus. The total number of corticospinal neurons in the arm representations of the premotor areas equals or exceeds the total number in the arm representation of the primary motor cortex. The premotor areas collectively comprise more than 60% of the cortical area in the frontal lobe that projects to the spinal cord. Like the primary motor cortex, each of the premotor areas contains local regions that have a high density of corticospinal neurons. These observations indicate that a substantial component of the corticospinal system originates from the premotor areas in the frontal lobe. Each of the premotor areas has direct access to the spinal cord, and as a consequence, each has the potential to influence the generation and control of movement independently of the primary motor cortex. These findings raise serious questions about the utility of viewing the primary motor cortex as the "upper motoneuron" or "final common pathway" for the central control of movement.
我们确定了额叶皮质脊髓神经元的起源。在将示踪剂注射到第二颈椎节段的背外侧索或整个颈膨大脊髓灰质后，这些神经元通过示踪剂的逆行运输进行标记。在另一组动物中，利用示踪剂从初级运动皮层的手臂区域进行逆行运输，我们确定了每个运动前区的手臂代表区。我们发现，投射到脊髓颈段的皮质脊髓束起源于初级运动皮层和额叶的6个运动前区。这些运动前区与直接投射到初级运动皮层手臂区域的区域相同。运动前区位于半球外侧表面和内侧壁的细胞构筑区6的部分区域，以及扣带沟中23区和24区的子区域。运动前区手臂代表区的皮质脊髓神经元总数等于或超过初级运动皮层手臂代表区的总数。运动前区共同构成了额叶中投射到脊髓的皮质区域的60%以上。与初级运动皮层一样，每个运动前区都包含皮质脊髓神经元高密度的局部区域。这些观察结果表明，皮质脊髓系统的一个重要组成部分起源于额叶的运动前区。每个运动前区都可直接与脊髓相连，因此，每个运动前区都有可能独立于初级运动皮层影响运动的产生和控制。这些发现对将初级运动皮层视为运动中枢控制的“上运动神经元”或“最后公路”的实用性提出了严重质疑。
