Neurogenesis

Neurogenesis is the process by which new neurons are born from neural stem cells. While it dominates fetal development, a more limited form continues in the adult brain — concentrated in the hippocampus, a structure central to memory, learning, and emotional regulation.

The extent of adult neurogenesis in humans remains an active area of research, and some aspects are still contested. What is well established is that the dentate gyrus of the hippocampus generates new neurons throughout life, and that this process is sensitive to both internal physiological conditions and external substances.

How it works · its role

New neurons arise from stem cells in the subgranular zone of the hippocampal dentate gyrus. These cells divide, differentiate, and gradually migrate into surrounding tissue, developing the synaptic connections needed to become functionally integrated — a process that unfolds over several weeks.

A number of molecular signals regulate whether this happens. Brain-derived neurotrophic factor (BDNF) is a key promoter, supporting cell survival and integration into existing circuits. Stress hormones, particularly glucocorticoids such as cortisol, tend to suppress the process. Physical exercise, sleep, and cognitively enriched environments are among the factors that support it.

Relevance to substances & effects

Antidepressants — SSRIs in particular — are among the most studied pharmacological promoters of hippocampal neurogenesis in animal models. Their neurogenic effect builds over weeks, roughly paralleling the delayed onset of clinical antidepressant action. This has led to the hypothesis that new neuron growth may contribute to mood recovery, though whether it is necessary, sufficient, or incidental is still debated.

Ketamine produces a much faster antidepressant response and is associated with rapid upregulation of BDNF and broad neuroplasticity in the hippocampus. Whether this extends meaningfully to new neuron formation in humans is less clear.

Classic psychedelics such as psilocybin and LSD promote neuroplasticity more broadly — including dendritic growth and synaptogenesis — and some preclinical evidence points toward neurogenic effects. Human data remain limited. These overlapping plasticity mechanisms are part of the rationale behind ongoing therapeutic research into this class.

Chronically heavy alcohol use, by contrast, is associated with suppression of hippocampal neurogenesis in animal studies. Recovery of this process during sustained abstinence is thought to contribute, in part, to the gradual cognitive improvements some people experience.