The dentate gyrus is one of the two gyri that constitute the hyppocampus; the other is the Ammon's horn. The dentate gyrus contains two regions: the fascia dentata and the hilus. It is also composed of three layers of neurons: molecular, granular, and polymorphic. The middle layer is most prominent and contains granule cells that project to the CA3 subfield of the hippocampus. The granule cells axons project mostly to interneurons, but also to pyramidal cells; they are the principal excitatory neurons of the dentate gyrus. The major input to the dentate gyrus is from layer 2 of the entorhinal cortex; the fibers connecting the layer 2 of the entorhinal cortex with dentate gyrus is called perforant pathway. This region of the hippocampus receives no direct inputs from other cortical structures.
The dentate gyrus provides some of the most remarkable examples of plasticity within the nervous system. In addition, it is critical to normal cognitive function, although exactly how and when is still a question that eludes answers. Furthermore, abnormalities within the dentate gyrus appear to play a role in diverse clinical conditions, from depression to epilepsy and traumatic brain injury. It is thought that the dentate gyrus contributes to the formation of new memories as well as other functional roles. It is notable as being one of a select few brain structures currently known to have high rates of neurogenesis, which is the process by which neurons are generated; other sites include the olfactory bulb and cerebellum.