Zeidman Peter, Mullally Sinéad L, Schwarzkopf Dietrich Samuel, Maguire Eleanor A
Wellcome Trust Centre for Neuroimaging, Institute of Neurology, University College London, London, UK.
Neuroreport. 2012 May 30;23(8):503-7. doi: 10.1097/WNR.0b013e328353766a.
The posterior parahippocampal cortex (PHC) supports a range of cognitive functions, in particular scene processing. However, it has recently been suggested that PHC engagement during functional MRI simply reflects the representation of three-dimensional local space. If so, PHC should respond to space in the absence of scenes, geometric layout, objects or contextual associations. It has also been reported that PHC activation may be influenced by low-level visual properties of stimuli such as spatial frequency. Here, we tested whether PHC was responsive to the mere sense of space in highly simplified stimuli, and whether this was affected by their spatial frequency distribution. Participants were scanned using functional MRI while viewing depictions of simple three-dimensional space, and matched control stimuli that did not depict a space. Half the stimuli were low-pass filtered to ascertain the impact of spatial frequency. We observed a significant interaction between space and spatial frequency in bilateral PHC. Specifically, stimuli depicting space (more than nonspatial stimuli) engaged the right PHC when they featured high spatial frequencies. In contrast, the interaction in the left PHC did not show a preferential response to space. We conclude that a simple depiction of three-dimensional space that is devoid of objects, scene layouts or contextual associations is sufficient to robustly engage the right PHC, at least when high spatial frequencies are present. We suggest that coding for the presence of space may be a core function of PHC, and could explain its engagement in a range of tasks, including scene processing, where space is always present.
海马旁回后部皮质（PHC）支持一系列认知功能，尤其是场景处理。然而，最近有人提出，功能磁共振成像（fMRI）期间PHC的参与仅仅反映了三维局部空间的表征。如果是这样，那么在没有场景、几何布局、物体或上下文关联的情况下，PHC应该对空间做出反应。也有报道称，PHC的激活可能会受到刺激的低水平视觉属性（如空间频率）的影响。在这里，我们测试了PHC在高度简化的刺激中是否仅对空间感有反应，以及这是否会受到其空间频率分布的影响。在参与者观看简单三维空间的描绘以及未描绘空间的匹配对照刺激时，使用功能磁共振成像对他们进行扫描。一半的刺激进行了低通滤波，以确定空间频率的影响。我们在双侧PHC中观察到空间和空间频率之间存在显著的相互作用。具体而言，描绘空间的刺激（比非空间刺激更能）在具有高空间频率时会激活右侧PHC。相比之下，左侧PHC中的相互作用并未显示出对空间的优先反应。我们得出结论，至少在存在高空间频率时，一个没有物体、场景布局或上下文关联的简单三维空间描绘足以强烈激活右侧PHC。我们认为，对空间存在的编码可能是PHC的核心功能，并且可以解释它在一系列任务中的参与情况，包括场景处理，在这些任务中空间总是存在的。
