Fig. 1 ∣. Schematic of mechanisms driving each proposed theory of dentate gyrus function.

a, Schematic of anatomical connections and circuitry within the dentate gyrus (DG). Layer II of the entorhinal cortex (EC) sends excitatory projections to the outer two-thirds of the DG molecular layer and directly to CA3. Granule cells (GCs) in the DG GC layer send excitatory projections to CA3. The GC layer of the DG encloses a polymorph layer that contains many cell types, including mossy cells (MCs) that send excitatory projections to the inner one-third of the molecular layer. The subgranular zone is a site of adult neurogenesis. Multiple interneuron types can be found throughout all layers of the DG. b, Pattern separation by expansion recoding: similar patterns of activity in the EC (active pyramidal, stellate and fan cells in red) elicit distinct patterns of activity among a relatively larger number of GCs, which in turn activate distinct populations of cells in CA3. c, Binding: the convergence of inputs from the lateral and medial EC upon DG GCs facilitates the binding of information carried by each stream. d, Novelty detection: enhanced excitability in the DG during novel experiences facilitates the encoding of new information. e, Gate or filter: strong feedforward and feedback inhibition work together to filter inputs such that only the strongest and most consistent inputs pass through the DG. MC projections contribute to feedback inhibition and the potentiation of synapses with coincident entorhinal and MC input. f, Engram: representations of an experience are maintained by a distinct population of GCs, and reactivation of this population facilitates memory recall. g, Indexing (a recent variant that incorporates adult neurogenesis): immature adult-born neurons (blue) maintain activity that is selective for experiences that occurred during their development, and the reactivation of this unique population aids in indexing neocortical representations of those experiences. h, Temporal tagging: the continuous turnover of immature adult-born cells over time gives rise to distinct populations of later mature adult-born cells with activity that is selective to (and re-engaged by) experiences that occurred at a particular time point. LEC, lateral entorhinal cortex; MEC, medial entorhinal cortex.