Bisley J W, Pasternak T
Department of Neurobiology & Anatomy and Center for Visual Science, University of Rochester, Rochester, NY 14642, USA.
Cereb Cortex. 2000 Nov;10(11):1053-65. doi: 10.1093/cercor/10.11.1053.
Although the role of cortical areas MT and MST (MT/MST) in the processing of directional motion information is well established, little is known about the way these areas contribute to the execution of complex behavioral tasks requiring the use of such information. We tested monkeys with unilateral lesions of these areas on a visual working memory task in which motion signals not only had to be encoded, but also stored for brief periods of time and then retrieved. The monkeys compared the directions of motion of two random-dot stimuli, sample and test, separated by a temporal delay. By increasing the temporal delay and spatially separating the two stimuli, placing one in the affected visual field and the other in the intact visual field, we were able to assess the contribution of MT/MST to specific components of the task: encoding (sample), retention (delay) and encoding/retrieval/comparison (test). We found that the effects of MT/MST lesions on specific components depended upon the demands of the task and the nature of the visual motion stimuli. Whenever stimuli consisted of random dots moving in a broad range of directions, MT/MST lesions appeared to affect encoding. Furthermore, when the lesions affected encoding of the sample, retention of the direction of stimulus motion was also affected. However, when the stimulus was coherent and the emphasis of the task was on the comparison of small direction differences, the absence of MT/MST had major impact on the retrieval/comparison component of the task and not on encoding or storage.
尽管大脑皮层MT区和MST区（MT/MST）在定向运动信息处理中的作用已得到充分证实，但对于这些区域如何促成需要利用此类信息的复杂行为任务的执行，我们却知之甚少。我们对这些区域单侧受损的猴子进行了一项视觉工作记忆任务测试，在该任务中，运动信号不仅要被编码，而且要短暂存储然后提取。猴子要比较两个随机点刺激（样本和测试刺激）的运动方向，这两个刺激之间有时间延迟。通过增加时间延迟并在空间上分离这两个刺激，将一个置于受影响视野，另一个置于未受损视野，我们能够评估MT/MST对任务特定组成部分的贡献：编码（样本）、保持（延迟）以及编码/提取/比较（测试）。我们发现，MT/MST损伤对特定组成部分的影响取决于任务要求和视觉运动刺激的性质。只要刺激由在广泛方向上移动的随机点组成，MT/MST损伤似乎就会影响编码。此外，当损伤影响样本的编码时，刺激运动方向的保持也会受到影响。然而，当刺激是连贯的且任务重点在于小方向差异的比较时，MT/MST的缺失对任务的提取/比较组成部分有重大影响，而对编码或存储没有影响。
