The Primary Visual Cortex Is Differentially Modulated by Stimulus-Driven and Top-Down Attention

Selective attention can be focused either volitionally, by top-down signals derived from task demands, or automatically, by bottom-up signals from salient stimuli. Because the brain mechanisms that underlie these two attention processes are poorly understood, we recorded local field potentials (LFPs) from primary visual cortical areas of cats as they performed stimulus-driven and anticipatory discrimination tasks. Consistent with our previous observations, in both tasks, we found enhanced beta activity, which we have postulated may serve as an attention carrier. We characterized the functional organization of task-related beta activity by (i) cortical responses (EPs) evoked by electrical stimulation of the optic chiasm and (ii) intracortical LFP correlations. During the anticipatory task, peripheral stimulation that was preceded by high-amplitude beta oscillations evoked large-amplitude EPs compared with EPs that followed low-amplitude beta. In contrast, during the stimulus-driven task, cortical EPs preceded by high-amplitude beta oscillations were, on average, smaller than those preceded by low-amplitude beta. Analysis of the correlations between the different recording sites revealed that beta activation maps were heterogeneous during the bottom-up task and homogeneous for the top-down task. We conclude that bottom-up attention activates cortical visual areas in a mosaic-like pattern, whereas top-down attentional modulation results in spatially homogeneous excitation.

选择性注意可通过两种途径实现聚焦：其一为依托任务需求产生的自上而下信号进行主动调控，其二为由显著性刺激引发的自下而上信号完成自动捕获。由于目前对这两类注意过程的脑机制尚缺乏深入认知，我们在猫执行刺激驱动型辨别任务与预期型辨别任务时，记录了其初级视觉皮层区域的局部场电位（local field potentials, LFPs）。
与我们此前的观测结果一致，两项任务中均检测到增强的β波段活动，我们推测该活动可作为注意载体发挥功能。我们通过两种方式对任务相关β波段活动的功能组织进行了表征：（i）视交叉电刺激诱发的皮层反应（EPs），以及（ii）皮层内局部场电位相关性分析。
在预期型辨别任务中，相较于低振幅β振荡紧随其后的皮层反应，先行出现高振幅β振荡的外周刺激所诱发的皮层反应振幅显著更高。与之相反，在刺激驱动型任务中，先行出现高振幅β振荡的皮层反应平均振幅要低于先行出现低振幅β振荡的对应情况。
对不同记录位点间相关性的分析结果显示，自下而上任务中的β激活图谱呈异质性分布，而自上而下任务中的β激活图谱则呈现空间均匀一致性。我们据此得出结论：自下而上注意以镶嵌样模式激活视觉皮层区域，而自上而下的注意调控则会引发空间上均匀一致的皮层兴奋。