Le T H, Pardo J V, Hu X
Department of Radiology and Center for Magnetic Resonance Research, University of Minnesota, Minneapolis 55455, USA.
J Neurophysiol. 1998 Mar;79(3):1535-48. doi: 10.1152/jn.1998.79.3.1535.
Regional blood oxygenation in the cerebellum and posterior cerebral cortices was monitored with functional magnetic resonance imaging (fMRI) at four Tesla while 16 normal subjects performed three tasks with identical visual stimulation: fixation; attention focused upon either stimulus shape or color and sustained during blocks of trials (sustained attention); and rapid, serial shifts in attention between stimulus shape or color within blocks of trials (shifting attention). The stimuli were displayed centrally for 100 ms followed by a central fixation mark for 900 ms. Each stimulus was either a circle or a square displayed in either red or green. Attention shifting required switching between color and shape information after each target detection and occurred on average once every three seconds. Subjects pressed a response key upon detecting the target; reaction time and response accuracy were recorded. Two protocols for T2*-weighted echo-planar imaging were optimized, one with a surface coil for the cerebellum alone and the other with a volume coil for imaging both cerebellum and posterior brain structures (parietal, occipital, and part of temporal cortices). Because fMRI of the cerebellum is particularly susceptible to cardiac and respiratory fluctuations, novel techniques were applied to isolate brain activation signals from physiological noise. Functional activation maps were generated for contrasts of 1) sustained attention to color minus fixation; 2) sustained attention to shape minus fixation; and 3) shifting attention minus sustained attention (to color and shape; i.e., summed across blocks of trials). Consistent with the ease of these tasks, subjects performed with >80% accuracy during both sustained attention and shifting attention. Analysis of variance did not show significant differences in false alarms or true hits across either attentional condition. A subgroup of subjects whose performance data were recorded during ten minutes of continuous practice did not show significant changes over time. Both contrasts between the conditions of sustained attention to color or to shape as compared with the fixation condition showed significant bilateral activation in occipital and inferior temporal regions (Brodmann areas 18, 19, and 37). The anterior medial cerebellum was also significantly activated ipsilateral to the finger used for responding. The principal comparison of interest, the contrast between the condition of shifting attention and the condition of sustained attention produced significant and reproducible activation: lateral cerebellar hemisphere (ansiform lobule: Crus I Anterior and Crus I Posterior; left Crus I Posterior); cerebellar folium; posterior superior parietal lobule (R and L); and cuneus and precuneus (R and L).
在4特斯拉的磁场强度下，利用功能磁共振成像（fMRI）对16名正常受试者在进行三项具有相同视觉刺激的任务时小脑和大脑后皮质的局部血氧合情况进行监测：注视；注意力集中于刺激形状或颜色并在试验组中持续保持（持续注意力）；以及在试验组内快速、连续地在刺激形状或颜色之间转移注意力（转移注意力）。刺激物在中央显示100毫秒，随后是中央注视标记900毫秒。每个刺激物要么是红色或绿色显示的圆形，要么是方形。注意力转移要求在每次目标检测后在颜色和形状信息之间切换，平均每三秒发生一次。受试者在检测到目标时按下反应键；记录反应时间和反应准确性。优化了两种用于T2 *加权回波平面成像的方案，一种使用仅针对小脑的表面线圈，另一种使用针对小脑和后脑结构（顶叶、枕叶和部分颞叶皮质）成像的容积线圈。由于小脑的功能磁共振成像特别容易受到心脏和呼吸波动的影响，因此应用了新技术来从生理噪声中分离出大脑激活信号。生成了功能激活图，用于对比以下情况：1）对颜色的持续注意力减去注视；2）对形状的持续注意力减去注视；以及3）转移注意力减去持续注意力（对颜色和形状；即跨试验组求和）。与这些任务的简易程度一致，受试者在持续注意力和转移注意力期间的准确率均超过80%。方差分析未显示在任何注意力条件下虚报或正确命中方面存在显著差异。在连续练习十分钟期间记录了表现数据的一组受试者，其表现未随时间显示出显著变化。与注视条件相比，对颜色或形状的持续注意力条件之间的两种对比均显示枕叶和颞下回区域（布罗德曼区18、19和37）出现显著的双侧激活。小脑前内侧也在用于反应的手指同侧显著激活。主要感兴趣的对比，即转移注意力条件与持续注意力条件之间的对比产生了显著且可重复的激活：小脑外侧半球（半月小叶：I小叶前部和I小叶后部；左侧I小叶后部）；小脑小叶；顶叶后上小叶（右侧和左侧）；以及楔叶和楔前叶（右侧和左侧）。
