Hippocampal Neurogenesis: Effects of Psychedelic Drugs

Abstract Neurogenesis, or the birth of new neurons, occurs throughout the human life span in the hippocampus, a structural node in the neural circuitry responsible for memory and learning. The process of neurogenesis involves proliferation of neural stem/progenitor cells and their differentiation into mature neurons, followed by integration into hippocampal circuitry. The function of new neurons in the hippocampus is not completely understood. The formation of new synaptic connections (and pruning of synapses) between neurons in the hippocampal dentate gyrus and fibers to and from the cerebral cortex is important in the acquisition of new associations (learning), recall of those associations (memory), and extinction of associations (forgetting). Very likely, the new neurons play a role in encoding temporal aspects of episodic memory. Neurogenesis is influenced by many factors, including physical activity, stress, depression, seizures, irradiation, aging, and a variety of psychoactive drugs. Many psychedelic drugs are shown to have an impact on hippocampal neurogenesis in a dose-dependent manner and to alter some aspects of memory and learning. Drug-induced alterations in hippocampal neurogenesis have been shown to alleviate depression and to have beneficial effects on conditioned fear. In light of abundant preclinical data and the loosening of governmental restrictions on psychedelic drug research, these agents should be explored for their therapeutic potential in depression, posttraumatic stress disorders, and drug dependence.