Laminar Organization of Working Memory Signals in Human Visual Cortex

• Published in: Current biology Vol. 28; no. 21; pp. 3435 - 3440.e4
• Main Authors: Lawrence, Samuel J.D., van Mourik, Tim, Kok, Peter, Koopmans, Peter J., Norris, David G., de Lange, Floris P.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 05.11.2018
• Subjects: feedback; laminar fMRI; visual cortex; visual working memory; feedback; laminar fMRI; visual working memory; visual cortex
• ISSN: 0960-9822; 1879-0445
• DOI: 10.1016/j.cub.2018.08.043

The human primary visual cortex (V1) is not only activated by incoming visual information but is also engaged by top-down cognitive processes, such as visual working memory, even in the absence of visual input [1–3]. This feedback may be critical to our ability to visualize specific visual features, as higher-order regions lack the selectivity to represent such information [4]. Clearly, such internally generated signals do not trigger genuine perception of the remembered stimulus, meaning they must be organized in a manner that is different to bottom-up-driven signals. Internally generated signals may be kept separate from incoming sensory data by virtue of the laminar organization of inter-area cortical connections. Namely, bottom-up driving connections target layer 4, located in the middle of the cortical column, and feedback connections target deep and superficial layers and avoid layer 4 [5–7]. Using lamina-resolved fMRI, we simultaneously measured the activity in three early visual cortical areas (V1–V3) that are recruited to represent stimulus information during visual working memory [8]. We observed item-specific working memory signals in early visual cortex. In V1, this item-specific activity was selectively present at deep and superficial cortical depths, avoiding the middle layers, and working-memory-related activity was present at all depths in V2 and V3. These results show for the first time the laminar organization of internally generated signals during visual working memory in the human visual system and provide new insights into how bottom-up and top-down signals in visual cortex are deployed. •Early visual cortex contains item-specific working memory signals•Working-memory-related activity is strongest in the agranular layers of V1•Working-memory-related activity is present at all depths in V2 and V3 Using high-field MRI, Lawrence et al. show that holding a visual item in working memory leads to top-down activation of the primary visual cortex. This activity is strongest in the agranular layers. These results provide new insights into how bottom-up and top-down signals are deployed in visual cortex.