Kimmig H, Greenlee M W, Gondan M, Schira M, Kassubek J, Mergner T
Neurologische Universitätsklinik, Breisacher Str. 64, 79106 Freiburg, Germany.
Exp Brain Res. 2001 Nov;141(2):184-94. doi: 10.1007/s002210100844.
We investigated the quantitative relationship between saccadic activity (as reflected in frequency of occurrence and amplitude of saccades) and blood oxygenation level dependent (BOLD) changes in the cerebral cortex using functional magnetic resonance imaging (fMRI). Furthermore, we investigated quantitative changes in cortical activity associated with qualitative changes in the saccade task for comparable levels of saccadic activity. All experiments required the simultaneous acquisition of eye movement and fMRI data. For this purpose we used a new high-resolution limbus-tracking technique for recording eye movements in the magnetic resonance tomograph. In the first two experimental series we varied both frequency and amplitude of saccade stimuli (target jumps). In the third series we varied task difficulty; subjects performed either pro-saccades or anti-saccades. The brain volume investigated comprised the frontal and supplementary eye fields, parietal as well as striate cortex, and the motion sensitive area of the parieto-occipital cortex. All these regions showed saccade-related BOLD responses. The responses in these regions were highly correlated with saccade frequency, indicating that repeated processing of saccades is integrated over time in the BOLD response. In contrast, there was no comparable BOLD change with variation of saccade amplitude. This finding speaks for a topological rather than activity-dependent coding of saccade amplitudes in most cortical regions. In the experiments comparing pro- vs anti-saccades we found higher BOLD activation in the "anti" task than in the "pro" task. A comparison of saccade parameters revealed that saccade frequency and cumulative amplitude were comparable between the two tasks, whereas reaction times were longer in the "anti" task than the pro task. The latter finding is taken to indicate a more demanding cortical processing in the "anti" task than the "pro" task, which could explain the observed difference in BOLD activation. We hold that a quantitative analysis of saccade parameters (especially saccade frequency and latency) is important for the interpretation of the BOLD changes observed with visual stimuli in fMRI.
我们使用功能磁共振成像（fMRI）研究了扫视活动（以扫视的发生频率和幅度反映）与大脑皮层血氧水平依赖（BOLD）变化之间的定量关系。此外，我们还研究了在扫视活动水平相当的情况下，与扫视任务定性变化相关的皮层活动的定量变化。所有实验都需要同时采集眼动和fMRI数据。为此，我们使用了一种新的高分辨率角膜缘追踪技术，用于在磁共振断层扫描仪中记录眼动。在前两个实验系列中，我们改变了扫视刺激（目标跳跃）的频率和幅度。在第三个系列中，我们改变了任务难度；受试者执行顺向扫视或逆向扫视。所研究的脑区包括额叶和辅助眼区、顶叶以及纹状皮层，还有顶枕叶皮层的运动敏感区。所有这些区域都显示出与扫视相关的BOLD反应。这些区域的反应与扫视频率高度相关，表明扫视的重复处理在BOLD反应中随时间整合。相比之下，扫视幅度变化时没有可比的BOLD变化。这一发现表明，在大多数皮层区域，扫视幅度的编码是拓扑性的，而非依赖于活动。在比较顺向扫视与逆向扫视的实验中，我们发现“逆向”任务中的BOLD激活高于“顺向”任务。扫视参数的比较显示，两个任务之间的扫视频率和累积幅度相当，而“逆向”任务中的反应时间比“顺向”任务长。后一个发现表明，“逆向”任务比“顺向”任务需要更复杂的皮层处理，这可以解释观察到的BOLD激活差异。我们认为，对扫视参数（尤其是扫视频率和潜伏期）进行定量分析，对于解释fMRI中视觉刺激时观察到的BOLD变化很重要。
