Preserved stimulus representations in frontal cortex as a potential neural mechanism for flexible control in working memory

Summary The nature and functions of stimulus-specific representations in different cortical regions have remained debatable in working memory research. Here we tested the account that high-dimensional stimulus representations emerge and persist in frontal cortex to facilitate flexible control in working memory. During functional magnetic resonance imaging, human participants flexibly switched between memorizing an orientation (maintenance) and categorizing an orientation following different learned rules (control) on a trial-by-trial basis. Our results demonstrated increased stimulus representations in frontal cortex that tracked demands on control, and increased stimulus representations in early visual cortex that tracked demands on precise maintenance. Simulations from two-module recurrent neural network models replicated human neural patterns, when stimulus information was preserved for readout at the output stage. Altogether, these findings provide empirical and computational evidence that preserved stimulus representations in higher-order cortex for output selection might serve as a possible coding scheme for the brain to accommodate the ever-changing environment.