What is hippocampus?
The hippocampus is a structure in the medial temporal lobe critical for memory formation, spatial navigation, and the imagination of future scenarios. It is part of the limbic system and connects to the Default Mode Network.
Key Functions
- •Memory — formation of new memories, consolidation
- •Spatial navigation — cognitive maps, "mental GPS"
- •Future simulation — reconstructing past experiences to model new scenarios
- •Context — binding events to time and place
Why does the hippocampus matter?
The hippocampus matters because without it, people cannot reliably form new memories of facts and events. The famous patient H.M., who had both hippocampi removed to treat epilepsy, could still hold a conversation and learn new motor skills but could not remember new experiences for more than a few minutes.
The hippocampus is also one of the few brain regions where new neurons are produced in adulthood in many mammals. Whether this happens to a meaningful degree in adult humans is still debated, and evidence is mixed.
What affects the hippocampus?
Sleep, stress, physical activity, and age all affect the hippocampus. During deep sleep, it replays recent experiences, which helps move memories into longer-term storage in the cortex, so poor sleep can impair memory formation.
The hippocampus has many receptors for cortisol, making it sensitive to stress hormones. Long-term stress and conditions such as depression and Cushing's syndrome have been associated with smaller hippocampal volume. Regular aerobic exercise has been linked to maintained or increased hippocampal volume in some studies. The hippocampus is also among the first regions affected in Alzheimer's disease, which is why memory problems are an early symptom.
In ONDA Life
Part 9 links the hippocampus and medial PFC for "mental modeling" — playing out future scenarios. The hippocampus reconstructs past experiences to model new possibilities, enabling imagination as a tool for behavioral engineering.