Aglioti S, Berlucchi G, Pallini R, Rossi G F, Tassinari G
Istituto di Fisiologia umana, Università di Verona, Italy.
Exp Brain Res. 1993;95(1):151-65. doi: 10.1007/BF00229664.
Normally, simple digital or manual responses to a light stimulus in the right or left visual hemifields are performed faster with uncrossed hand-field combinations than with crossed hand-field combinations. Because of the organization of visual and motor pathways, the integration of uncrossed responses is assumed to occur within a single hemisphere, whereas a time-consuming interhemispheric transfer via the corpus callosum is considered to be necessary for the integration of crossed responses. However, callosal transfer may be dispensable for those crossed responses which can be controlled through ipsilaterally descending motor pathways by the hemisphere receiving the visual stimulus. We investigated crossed-uncrossed differences (CUDs) in speed of simple visuomotor responses to lateralized flashes in one subject with total section of the corpus callosum and two subjects with complete callosal agenesis. We recorded the reaction times as well as the premotor times, as indicated by the electromyographic latencies of the prime movers, of three types of responses: a distal response involving a thumb flexion, a proximal response chiefly involving a forearm flexion and an axial response involving a shoulder elevation. Further, the three types of responses to a single lateralised flash were performed both unilaterally and bilaterally. The three acallosal subjects showed CUDs greatly exceeding normal values on distal responses, either unilateral or bilateral, and on unilateral proximal responses. These abnormally long CUDs stood in sharp contrast to the insignificant CUDs exhibited by the same subjects on bilateral proximal responses and on unilateral and bilateral axial responses in agreement with correspondingly insignificant CUDs reported for normal subjects. These results confirm that a callosal contribution is important for the execution of fast distal and unilateral proximal responses to a visual stimulus directed to the hemisphere ipsilateral to the responding hand. By contrast, the other types of crossed responses appear to be efficiently coordinated across the midline without the aid of the corpus callosum. This is in keeping with the hypothesis that they are governed by a bilaterally distributed motor system which is preferentially activated for the execution of symmetrical bilateral movements, employing axial and proximal limb muscles.
通常情况下，对于右侧或左侧视野中的光刺激，简单的数字或手动反应在同侧手-视野组合下比交叉手-视野组合下执行得更快。由于视觉和运动通路的组织方式，同侧反应的整合被认为发生在单个半球内，而交叉反应的整合则被认为需要通过胼胝体进行耗时的半球间传递。然而，对于那些可以由接收视觉刺激的半球通过同侧下行运动通路控制的交叉反应，胼胝体传递可能是不必要的。我们研究了一名胼胝体完全切断的受试者和两名胼胝体完全缺失的受试者对侧方闪光的简单视觉运动反应速度的交叉-同侧差异（CUDs）。我们记录了三种类型反应的反应时间以及运动前时间，运动前时间由原动肌的肌电图潜伏期表示：一种是涉及拇指屈曲的远端反应，一种主要涉及前臂屈曲的近端反应，以及一种涉及肩部抬高的轴向反应。此外，对单个侧方闪光的三种类型反应分别以单侧和双侧方式进行。这三名无胼胝体受试者在单侧或双侧远端反应以及单侧近端反应上表现出的CUDs大大超过正常值。这些异常长的CUDs与这些受试者在双侧近端反应以及单侧和双侧轴向反应上表现出的不显著CUDs形成鲜明对比，而正常受试者相应的CUDs也不显著。这些结果证实，胼胝体对执行针对与反应手同侧半球的视觉刺激的快速远端和单侧近端反应很重要。相比之下，其他类型的交叉反应似乎在没有胼胝体帮助的情况下能有效地在中线两侧进行协调。这与以下假设一致，即它们由双侧分布的运动系统控制，该系统在执行对称双侧运动时优先被激活，使用轴向和近端肢体肌肉。
