Recurrent code for working memory maintenance in the human frontal cortex

Despite accumulating evidence for the involvement of frontal cortex in working memory, it remains debated whether frontal cortex stores stimulus-specific mnemonic information or coordinates mnemonic representations in sensory areas. Neurophysiological non-human primate studies at microcircuit level largely support the former view, while human neuroimaging findings at macroscale level remain inconsistent. Here, we leverage ultra-high-field (7T) functional magnetic resonance imaging (fMRI) to interrogate the nature of working memory representations in human frontal cortex at submillimeter resolution. Our results reveal decodable working memory contents in the superficial layers of superior precentral sulcus (sPCS), indicating recurrent working memory mechanisms. These mnemonic contents are represented in a continuous format, resembling those observed during encoding. Their fidelity depends on the spatial selectivity of individual voxels and the strength of persistent activity, and closely tracks working memory performance. Our findings highlight the recurrent code for working memory in human frontal cortex, reconciling cross-species controversy into a shared mechanistic framework of working memory.