THE ROLE OF THE DENTATE GYRUS IN THE IMPLEMENTATION OF THE HIPPOCAMPAL FUNCTIONS: HEALTHY BRAIN

The dentate gyrus (DG), part of the hippocampal formation, is the main target of the neocortical and subcortical afferents received by the hippocampus; these afferents constitute the anatomical basis for the involvement of the hippocampus in cognitive processes such as attention and memory. Namely in the DG a long-term potentiation was first discovered, - plastic changes in synapses, similar to those that occur when information memorizing. DG is a unique region of the brain, one of the few where neurogenesis is found in adult mammals, including humans. Another feature of the DG, which distinguishes it from the hippocampus, is the presence of two types of glutamatergic neurons, granular and mossy cells. Granular cells, normally having low excitability, restrict the activation of pyramidal neurons of the hippocampus and effectively restrain the flow of information passing through the hippocampal network. This property of granular neurons underlies the protective function of DG, which counteracts overexcitation of the hippocampal network. The functions of the mossy neurons of the DG are the least clear; these cells, innervating both glutamatergic and GABAergic neurons, are likely to participate in the organization of complex network activity both in the DG itself and in the hippocampus. Despite intensive investigation of the DG, its role in the activity of the hippocampus is still largely unclear. This review examines the anatomical, histochemical, and functional DG features, the activity of individual cellular elements, as well as its role in hippocampal functions of normal brain. Special attention is paid to unresolved issues in these aspects.