Weber B, Treyer V, Oberholzer N, Jaermann T, Boesiger P, Brugger P, Regard M, Buck A, Savazzi S, Marzi C A
University Hospital Zurich.
J Cogn Neurosci. 2005 Jan;17(1):113-23. doi: 10.1162/0898929052880002.
When both detections and responses to visual stimuli are performed within one and the same hemisphere, manual reaction times (RTs) are faster than when the two operations are carried out in different hemispheres. A widely accepted explanation for this difference is that it reflects the time lost in callosal transmission. Interhemispheric transfer time can be estimated by subtracting RTs for uncrossed from RTs for crossed responses (crossed-uncrossed difference, or CUD). In the present study, we wanted to ascertain the role of spatial attention in affecting the CUD and to chart the brain areas whose activity is related to these attentional effects on interhemispheric transfer. To accomplish this, we varied the proportion of crossed and uncrossed trials in different blocks. With this paradigm subjects are likely to focus attention either on the hemifield contralateral to the responding hand (blocks with 80% crossed trials) or on the ipsilateral hemifield (blocks with 80% uncrossed trials). We found an inverse correlation between the proportion of crossed trials in a block and the CUD and this effect can be attributed to spatial attention. As to the imaging results, we found that in the crossed minus uncrossed subtraction, an operation that highlights the neural processes underlying interhemispheric transfer, there was an activation of the genu of the corpus callosum as well as of a series of cortical areas. In a further commonality analysis, we assessed those areas which were activated specifically during focusing of attention onto one hemifield either contra- or ipsilateral to the responding hand. We found an activation of a number of cortical and subcortical areas, notably, parietal area BA 7 and the superior colliculi. We believe that the main thrust of the present study is to have teased apart areas important in interhemispheric transmission from those involved in spatial attention.
当对视觉刺激的检测和反应在同一半球内进行时，手动反应时间（RTs）比在不同半球进行这两种操作时要快。对此差异的一种广泛接受的解释是，它反映了胼胝体传递中损失的时间。半球间传递时间可以通过交叉反应的RTs减去非交叉反应的RTs来估计（交叉 - 非交叉差异，或CUD）。在本研究中，我们想确定空间注意力在影响CUD中的作用，并绘制出其活动与这些对半球间传递的注意力效应相关的脑区。为了实现这一点，我们在不同的组块中改变交叉和非交叉试验的比例。使用这种范式，受试者可能会将注意力集中在与反应手对侧的半视野（80%交叉试验的组块）或同侧半视野（80%非交叉试验的组块）上。我们发现组块中交叉试验的比例与CUD之间存在负相关，这种效应可归因于空间注意力。关于成像结果，我们发现在交叉减去非交叉的减法运算中，这一突出半球间传递潜在神经过程的操作，胼胝体膝部以及一系列皮质区域有激活。在进一步的共性分析中，我们评估了那些在将注意力集中到与反应手对侧或同侧的一个半视野期间特异性激活的区域。我们发现一些皮质和皮质下区域有激活，特别是顶叶BA 7区和上丘。我们认为本研究的主要重点是区分在半球间传递中重要的区域与参与空间注意力的区域。
