Sequential replay of non-spatial task states in the human hippocampus

Neurophysiological research has found that previously experienced sequences of spatial events are reactivated in the hippocampus of rodents during wakeful rest. This phenomenon has become a cornerstone of modern theories of memory and decision making. Yet, whether hippocampal sequence reactivation at rest is of general importance also for humans and non-spatial tasks has remained unclear. Here, we investigated sequences of fMRI BOLD activation patterns in humans during wakeful rest following a sequential non-spatial decision-making task. We found that pattern reactivations within the human hippocampus reflected the order of previous task state sequences, and that the extent of this offline reactivation was related to the on-task representation of task states in the orbitofrontal cortex. Permutation analyses and fMRI signal simulations confirmed that these results reflected underlying BOLD activity, and showed that our novel statistical analyses are, in principle, sensitive to sequential neural events occurring as fast as one hundred milliseconds apart. Our results support the importance of sequential reactivation in the human hippocampus for decision making, and establish the feasibility of investigating such rapid signals with fMRI, despite its substantial temporal limitations.\n\nHighlightsO_LIWe provide fMRI evidence for sequential pattern reactivation in the human hippocampus\nC_LIO_LISequences of patterns reflect states from a sequential, non-spatial decision-making task\nC_LIO_LISimulations show that our novel fMRI analysis is sensitive to fast sequences of sub-second neural events\nC_LIO_LIResults support the importance of sequential reactivation in the human hippocampus for decision making\nC_LI