Abstract
<title>Abstract</title> <p> The dentate gyrus (DG) transforms similar inputs into more distinct representations, a computation termed patternseparation, and is one of the few brain regions that generate new neurons throughout adulthood. These adult-born granule cells(GCs) pass through an immature, highly excitable stage, and activating them <italic>in vivo</italic> recruits inhibitory interneurons andincreases population sparsity across both the DG and CA3 (Cornu Ammonis area 3). Whether this circuit-wide effect follows from theknown DG--CA3 microcircuitry has not been examined in a biophysically detailed model, and existing models of neurogenesis andpattern separation are confined to the DG. Here, a spiking model of the DG--CA3 network was built from the Hippocampome.orgknowledge base and extended with a population of immature GCs (iGCs). Pattern separation and population sparsity were measuredwhile the level of neurogenesis and iGC excitability was varied, and the iGCs were then activated directly. Neurogenesis enhancedpattern separation in the mature GCs (mGCs) and pushed CA3 in the same direction, mainly by making population activity sparser;direct activation of the iGCs recruited inhibitory interneurons throughout the DG and CA3 and increased population sparsity,reproducing the effect observed <italic>in vivo</italic> . The sparsifying influence of adult neurogenesis can therefore emerge from theknown DG--CA3 circuitry and reaches beyond the DG, consistent with a modulatory rather than an encoding role for iGCs. </p>