Task-specific representational spaces for memory formation in the medial temporal lobe

Adaptive behavior requires stimuli to be processed in a way that meets the requirements of the current task. This is especially relevant for natural concepts that comprise a multitude of representational formats. The medial temporal lobe (MTL) has been proposed to support such flexibility by organizing stimuli within relational representational spaces serving as cognitive maps. However, while various studies investigated the formation of novel cognitive maps based on abstract features, it remains unclear how our vast existing conceptual knowledge is recruited into task-relevant representational spaces and whether these spaces influence the formation of novel episodic memories. Here we show that neural representations of natural concepts in the MTL and neocortex are embedded in low-dimensional representational spaces of task-relevant features that flexibly reorganize when task demands change. Crucially, hippocampal pattern similarity reflects task-relevant, but not task-irrelevant conceptual feature dimensions of the same set of natural concepts, indicating context-dependent reconfiguration of representational spaces. Euclidean distances within and across these spaces predicted subsequent memory confidence for individual items, suggesting a putative metric of task-dependent neural distinctiveness for the formation of memory traces. Finally, we dissociate task- and stimulus-dependent formats in neocortex, demonstrating complementary representations of natural stimuli that differentially contribute to memory formation. Our findings suggest that relational coding of task-relevant features in the MTL may serve as an index of representational distinctiveness that contributes to the formation of novel episodic memories and integrate MTL accounts based on spatial coding and episodic memory.