Challenges in replicating layer-specificity of working memory processes in human dlPFC

Although working memory reliably activates the dorsolateral prefrontal cortex (dlPFC), the functional significance of its distinct cytoarchitectonic layers is not well understood in humans. A recent functional magnetic resonance (fMRI) study at 7T demonstrated for the first time layer-specific responses in the human dlPFC during working memory. Superficial layers were more active during the delay period when working memory items needed to be manipulated compared to mere maintenance. In contrast, deeper layers were more active during the motor response to a probe compared to non-action. Like many current layer fMRI studies, this study relied on several manual and semi-manual processing steps, including the selection of regions of interest. To test the replicability of these findings, we conducted a pre-registered replication of this study in 21 subjects using a fully automated and reproducible analysis pipeline. Our results do not show the same layer-specific effects. Although we observed higher activity in the superficial layers in response to working memory manipulation during the delay period, we did not find any evidence for stronger deep layer involvement during motor response in the probe period. We argue that our results are biologically plausible in light of previous research as well as methodological considerations inherent in layer fMRI acquisition and analysis. Consequently, we conclude that the evidence regarding the functional role of different layers within the human dlPFC during working memory remains inconclusive. A focus on replicability, reproducibility, and a better understanding of the influence of methodological choices will help layer fMRI become a more routine tool in cognitive neuroscience.