Department of Neurophysiology, Max Planck Institute for Brain Research, Deutschordenstrasse 46, Frankfurt am Main, Germany.
Neuroimage. 2010 Jan 1;49(1):794-804. doi: 10.1016/j.neuroimage.2009.07.055. Epub 2009 Jul 29.
Visual imagery--similar to visual perception--activates feature-specific and category-specific visual areas. This is frequently observed in experiments where the instruction is to imagine stimuli that have been shown immediately before the imagery task. Hence, feature-specific activation could be related to the short-term memory retrieval of previously presented sensory information. Here, we investigated mental imagery of stimuli that subjects had not seen before, eliminating the effects of short-term memory. We recorded brain activation using fMRI while subjects performed a behaviourally controlled guided imagery task in predefined retinotopic coordinates to optimize sensitivity in early visual areas. Whole brain analyses revealed activation in a parieto-frontal network and lateral-occipital cortex. Region of interest (ROI) based analyses showed activation in left hMT/V5+. Granger causality mapping taking left hMT/V5+ as source revealed an imagery-specific directed influence from the left inferior parietal lobule (IPL). Interestingly, we observed a negative BOLD response in V1-3 during imagery, modulated by the retinotopic location of the imagined motion trace. Our results indicate that rule-based motion imagery can activate higher-order visual areas involved in motion perception, with a role for top-down directed influences originating in IPL. Lower-order visual areas (V1, V2 and V3) were down-regulated during this type of imagery, possibly reflecting inhibition to avoid visual input from interfering with the imagery construction. This suggests that the activation in early visual areas observed in previous studies might be related to short- or long-term memory retrieval of specific sensory experiences.
视觉意象——类似于视觉感知——激活了具有特定特征和类别特异性的视觉区域。这在实验中经常观察到，实验指令是想象之前立即呈现的刺激。因此，特征特异性激活可能与先前呈现的感觉信息的短期记忆检索有关。在这里，我们研究了受试者以前从未见过的刺激的心理意象，消除了短期记忆的影响。我们使用 fMRI 记录大脑激活，同时受试者在预定义的视网膜坐标中执行行为控制的引导意象任务，以优化早期视觉区域的灵敏度。全脑分析显示在顶叶-额叶网络和外侧枕叶皮层中存在激活。基于感兴趣区域 (ROI) 的分析显示左侧 hMT/V5+ 有激活。有趣的是，我们观察到在想象时 V1-3 中出现了负的 BOLD 反应，其被想象运动轨迹的视网膜位置调制。我们的结果表明，基于规则的运动意象可以激活参与运动感知的高阶视觉区域，并且 IPL 中的自上而下的定向影响起着作用。在这种类型的意象中，较低阶的视觉区域（V1、V2 和 V3）被下调，可能反映了抑制作用，以避免视觉输入干扰意象的构建。这表明，以前研究中观察到的早期视觉区域的激活可能与特定感觉体验的短期或长期记忆检索有关。
