Lawrence D G, Hopkins D A
Brain. 1976 Jun;99(2):235-54. doi: 10.1093/brain/99.2.235.
Corticospinal fibres terminate in three areas in the spinal grey matter of the rhesus monkey: the nucleus proprius of the dorsal horn, the intermediate zone and directly upon motoneurons, particularly those inervating limb muscles. It was suggested at their earliest discovery that direct corticomotoneuronal (CM) connections might constitute a critical anatomical substrate for the type of fractionated movement exemplified by relatively independent finger movements (RIFM). The present study was undertaken in an attempt to provide further evidence in support of this idea. The evidence is based upon the anatomical finding that few CM connections are present at birth in the monkey, the bulk being formed postnatally to reach an adult density at approximately 8 months of age. There were two experimental approaches: in the first it was argued that if RIFM are dependent upon the presence of CM connections it would be expected that such movements would appear only gradually postnatally, developing in parallel with the development of the connections. In 2 normal monkeys studied from this point of view discrete distal movements did develop only gradually with RIFM reaching an adult level at 7 to 8 months of age. The second experimental appraoch was based upon the fact that pyramidal lesions in newborn animals interrupt corticospinal fibres before CM connections are formed. It was argued that such a situation might provide a better opportunity for other descending pathways to establish the connections necessary for RIFM. Five infant monkeys had bilateral pyramidal tract lesions made from 5 days to 4 weeks after birth and were observed for a period of three years. In the 4 animals in which the lesions were complete, RIFM failed to develop. In the fifth animal, in which the lesions were incomplete, there was development of some degree of RIFM. It was concluded that the development of RIFM is dependent upon fibres passing in the pyramidal tracts and that in infant monkeys, as well as in adults, other descending pathways are unable to form the connections necessary for these movements. The possible contribution to RIFM of the corticospinal fibres arise in the somatosensory cortex and terminate in the dorsal horn was studied by bilateral removal of the arm and leg area of the somatosensory cortex in one animal. Since RIFM were only minimally and transiently altered, it was concluded that such movements are not dependent upon these fibres. The different lines of evidence presented in the study are interpreted as giving further support to the idea that corticomotoneuronal connections constitute an essential anatomical substrate for fractionated movements such as RIFM. Observations were also made of the development of general locomotor activity in normal and pyramidotomized infant monkeys.
背角固有核、中间带以及直接作用于运动神经元，尤其是那些支配肢体肌肉的运动神经元。在它们最早被发现时就有人提出，直接的皮质运动神经元（CM）连接可能构成了以相对独立的手指运动（RIFM）为代表的精细运动类型的关键解剖学基础。本研究旨在为这一观点提供进一步的证据。证据基于解剖学发现，即猴子出生时几乎没有CM连接，大部分是在出生后形成的，在大约8个月大时达到成年密度。有两种实验方法：第一种方法认为，如果RIFM依赖于CM连接的存在，那么可以预期这种运动只会在出生后逐渐出现，并与连接的发育同步发展。从这个角度研究的2只正常猴子中，离散的远端运动确实是逐渐发展的，RIFM在7到8个月大时达到成年水平。第二种实验方法基于这样一个事实，即新生动物的锥体束损伤会在CM连接形成之前中断皮质脊髓纤维。有人认为，这种情况可能为其他下行通路提供了一个更好的机会来建立RIFM所需的连接。5只幼猴在出生后5天到4周进行了双侧锥体束损伤，并观察了三年。在4只损伤完全的动物中，RIFM未能发育。在第5只动物中，损伤不完全，出现了一定程度的RIFM发育。得出的结论是，RIFM的发育依赖于通过锥体束的纤维，并且在幼猴以及成年猴中，其他下行通路无法形成这些运动所需的连接。通过在一只动物中双侧切除体感皮层的手臂和腿部区域，研究了起源于体感皮层并终止于背角的皮质脊髓纤维对RIFM的可能贡献。由于RIFM只是轻微且短暂地改变，得出的结论是这种运动不依赖于这些纤维。该研究中提出的不同证据线被解释为进一步支持了这样一种观点，即皮质运动神经元连接构成了诸如RIFM等精细运动的重要解剖学基础。还对正常和锥体束切断的幼猴的一般运动活动发育进行了观察。
