Elul Deena, McKyton Ayelet, Levin Netta
fMRI unit, Department of Neurology, Hadassah Medical Organization and Faculty of Medicine, The Hebrew University of Jerusalem, Ein Karem, Jerusalem, Israel.
Edmond and Lily Safra Center for Brain Sciences (ELSC), The Hebrew University of Jerusalem, Jerusalem, Israel.
Invest Ophthalmol Vis Sci. 2025 Sep 2;66(12):12. doi: 10.1167/iovs.66.12.12.
Behavioral and electrophysiological studies have shown that vision is slower under scotopic conditions (dark, activating only rods) than photopic conditions (light, activating only cones). However, slower scotopic processing cannot be solely explained by findings that rod signals are slower than cone signals, and it is unknown whether temporal processing differences persist in cortex. Flickering stimuli have previously been used in functional MRI (fMRI) studies to probe photopic cortical temporal sensitivity. This fMRI study investigates flicker sensitivity under photopic and scotopic conditions across the cortical visual hierarchy.
Fourteen participants viewed a stimulus flickering at six frequencies (2-10 Hz) under photopic and scotopic conditions during fMRI scanning. Retinotopic and high-level visual areas were delineated for each subject with population receptive field modeling (using a drifting bar) and a functional localizer (using images of objects).
In most areas, higher mean activation was observed under photopic than under scotopic conditions. However, peak activation was higher only in V1 and ventral retinotopic areas. The pattern of change over frequencies differed between lighting conditions in retinotopic areas, but not in most high-level areas. Under scotopic conditions, the largest BOLD response was observed at low frequencies throughout visual cortex. Under photopic conditions, BOLD responses appeared largely unchanging across frequencies, with a trend towards preferring higher frequencies in V1.
Selectivity for lower frequencies under scotopic conditions was observed throughout visual cortex, in contrast to limited selectivity under photopic conditions. This low-frequency preference could allow more time for extracting information from sparse scotopic stimuli.
行为学和电生理学研究表明，在暗视条件下（黑暗，仅激活视杆细胞）视觉比明视条件下（明亮，仅激活视锥细胞）更慢。然而，暗视处理较慢不能仅用视杆细胞信号比视锥细胞信号慢这一发现来解释，并且尚不清楚时间处理差异在皮层中是否持续存在。闪烁刺激先前已用于功能磁共振成像（fMRI）研究以探究明视皮层的时间敏感性。这项fMRI研究调查了在整个皮层视觉层级中明视和暗视条件下的闪烁敏感性。
14名参与者在fMRI扫描期间，在明视和暗视条件下观看以六种频率（2 - 10赫兹）闪烁的刺激。使用群体感受野建模（使用漂移条）和功能定位器（使用物体图像）为每个受试者描绘视网膜拓扑和高级视觉区域。
在大多数区域，明视条件下观察到的平均激活高于暗视条件下。然而，峰值激活仅在V1和腹侧视网膜拓扑区域更高。视网膜拓扑区域中频率变化模式在光照条件之间有所不同，但在大多数高级区域中并非如此。在暗视条件下，在整个视觉皮层的低频处观察到最大的血氧水平依赖（BOLD）反应。在明视条件下，BOLD反应在各频率上基本不变，在V1中有偏好更高频率的趋势。
与明视条件下有限的选择性相比，在整个视觉皮层中观察到暗视条件下对较低频率的选择性。这种低频偏好可以为从稀疏的暗视刺激中提取信息留出更多时间。
