Hippocampal subfields integrate information about past temporal and cognitive contexts

The hippocampus plays a critical role in supporting episodic memory. Although we know that temporal context is a defining feature of episodic memory, we understand relatively little about how this information may be represented by the hippocampus. Research in rodents has suggested that the hippocampus represents temporal information on an absolute scale or in terms of relative temporal intervals, but cognitive models of memory have argued that temporal context in episodic memory is a consequence of changes in cognitive states and experiences. Here, we combined high-resolution fMRI imaging with voxel pattern similarity analyses to answer the question of how human hippocampal subfields represent retrieved information about cognitive states and the time at which a past event took place. As participants recollected previously presented items, activity patterns in the CA23DG subregion carried information about prior cognitive states, along with coarse-grained information about when the item was previously encountered. These findings are consistent with the idea that CA23DG supports temporal context in episodic memory by encoding an integrated representation of discrete and gradually-changing cognitive states.