Redgrave P, Dean P, Westby G W
Department of Psychology, University of Sheffield, U.K.
Neuroscience. 1990;37(3):571-84. doi: 10.1016/0306-4522(90)90092-i.
The superior colliculus has been used to study principles of sensorimotor transformation underlying the guidance of orienting movements by multimodal sensory stimuli. We have previously suggested that there may be two different classes of mechanism which can produce orienting-like movements towards a novel event; one that locates a stimulus on the basis of remembered position, and another which uses continuous feedback relating to target velocity. The crossed descending pathway of the superior colliculus is widely considered the projection most likely to relay signals associated with the production of orienting movements. However, if different neural mechanisms are used to produce functionally distinct types of orienting, we might expect this pathway to have separate anatomical components related to function. The purpose of the present experiment was to see if collicular fibres innervating two important pre-motor targets of the crossed descending pathway, the periabducens area and the caudal medulla-spinal cord, come from the same population of tectal cells. One of the retrogradely transported fluorescent tracers (Diamidino Yellow) was injected into the periabducens area, and another (True Blue or Fast Blue) was injected into tectospinal fibres at the level of the ventromedial caudal medulla. Under these conditions we found: (i) less than 10% of labelled cells within the superior colliculus contained both tracers; (ii) the bulk of singly labelled cells projecting to the periabducens area or the caudal medulla were concentrated at different locations within the colliculus, (iii) in regions of the superior colliculus where there was overlap of singly labelled cells, neurons projecting to the periabducens area or the caudal medulla could be distinguished morphologically. These data provide three classes of evidence which indicate that the crossed descending projection in rat can be subdivided into at least two relatively independent anatomical components. This conclusion may, in part, provide an anatomical substrate for the functional dissociations proposed for orienting movements.
上丘已被用于研究多模式感觉刺激引导定向运动背后的感觉运动转换原理。我们之前曾提出，可能存在两种不同类型的机制，它们能够产生针对新事件的类似定向的运动；一种是根据记忆位置定位刺激，另一种则利用与目标速度相关的连续反馈。上丘的交叉下行通路被广泛认为是最有可能传递与定向运动产生相关信号的投射。然而，如果使用不同的神经机制来产生功能上不同类型的定向，我们可能会预期这条通路具有与功能相关的独立解剖成分。本实验的目的是观察支配交叉下行通路的两个重要运动前目标——外展神经周围区域和延髓尾侧脊髓的丘系纤维，是否来自同一群顶盖细胞。将一种逆行运输的荧光示踪剂（双脒基黄）注入外展神经周围区域，另一种（真蓝或快蓝）注入延髓尾侧腹内侧水平的顶盖脊髓纤维。在这些条件下，我们发现：（i）上丘内不到10%的标记细胞同时含有两种示踪剂；（ii）投射到外展神经周围区域或延髓尾侧的单个标记细胞大部分集中在上丘内的不同位置，（iii）在上丘中单个标记细胞重叠的区域，可以从形态上区分投射到外展神经周围区域或延髓尾侧的神经元。这些数据提供了三类证据，表明大鼠的交叉下行投射至少可以细分为两个相对独立的解剖成分。这一结论可能部分为定向运动所提出的功能分离提供了解剖学基础。
