Figure 3. Basic circuit architecture of adult hippocampus and a model on how new neurons impact the local circuitry.

Entorhinal cortical inputs innervate dentate gyrus granule cells, and dentate granule cells innervate CA3 neurons, which in turn innervate CA1 neurons. New granule cells innervate hilar interneurons, each of which inhibit hundreds of mature dentate granule cells. New granule cells also innervate hilar mossy cells, which activate many granule cells on the contralateral dentate gyrus. Through innervations of local interneurons and mossy cells, a single adult-born granule cell has the capacity to modulate the network activity at the circuitry level.