Temporal-Order-Based Attentional Priority Modulates Mnemonic Representations in Parietal and Frontal Cortices.

The respective roles of occipital, parietal, and frontal cortices in visual working memory maintenance have long been under debate. Previous work on whether parietal and frontal regions convey mnemonic information has yielded mixed findings. One possibility for this variability is that the mnemonic representations in high-level frontoparietal regions are modulated by attentional priority, such as temporal order. To test this hypothesis, we examined whether the most recent item, which has a higher attentional priority in terms of temporal order, is preferentially encoded in frontoparietal regions. On each trial, participants viewed 2 gratings with different orientations in succession, and were cued to remember one of them. Using fMRI and an inverted encoding model, we reconstructed population-level, orientation representations in occipital (V1-V3), parietal (IPS), and frontal (FEF) areas during memory maintenance. Unlike early visual cortex where robust orientation representations were observed regardless of serial order, parietal, and frontal cortices showed stronger representations when participants remembered the second grating. A subsequent experiment using a change detection task on color rings excluded the possibilities of residual stimulus-driven signals or motor preparative signals for responses. These results suggest that mnemonic representations in parietal and frontal cortices are modulated by temporal-order-based attentional priority signals.