Role in Memory Consolidation
The hippocampus temporarily holds new information and transfers it to the neocortex during sleep through the memory consolidation process. Experiences during wakefulness are initially encoded in hippocampal CA1-CA3 circuits, then reactivated during non-REM sleep via sharp-wave ripple events - high-frequency burst activity patterns. A leading explanatory model holds that when this reactivation synchronizes with cortical slow oscillations, memories become integrated into neocortical networks for long-term storage. Learning effects from cognitive testing are also explained in terms of this model: sleep following a test session is regarded as a factor that supports performance improvements on subsequent days. Without adequate post-learning sleep, consolidation is thought to suffer and skill gains to be smaller.
Neurogenesis and Plasticity
The dentate gyrus of the hippocampus has been studied as a site where new neurons are produced in adulthood (adult neurogenesis). It is clearly observed in rodents, while how much occurs in adult humans remains disputed as of August 2026. These newborn neurons are thought to contribute to pattern separation - the ability to distinguish between similar memories and experiences. Aerobic exercise promotes BDNF secretion and has been reported to push neurogenesis upward in animal models. MRI studies of London taxi drivers are often cited as showing an association between mastery of spatial navigation and the size of the posterior hippocampus. A single study cannot, however, establish the causal direction that training increased the volume. Plasticity of this kind is treated as one of the clues behind the idea of cognitive reserve.
Stress Vulnerability and Protection
The hippocampus expresses glucocorticoid receptors at high density, making it particularly vulnerable to sustained cortisol elevation from chronic stress. Animal studies have repeatedly observed dendritic shrinkage and reduced synaptic density in hippocampal neurons under chronic stress. In humans, reduced hippocampal volume has been documented in PTSD patients and those with chronic depression. Sleep deprivation also impairs hippocampal function, and the day after a night of poor sleep the encoding of new information tends to be at a disadvantage. Day-to-day variability in Bench scores may partly involve these hippocampal state changes. Regular exercise, stress management, and consistent sleep schedules are commonly cited as the central protective strategies for maintaining hippocampal health.