What does the hippocampus do?
Named after the Latin for seahorse (due to its shape), the hippocampus is made up of two parts of the brain, with one on each side. It helps process and form memories, retrieving them, and turning short-term into long-term memories. It deals with two specific types of memories: explicit and spatial. Explicit (or declarative) memories are related to memorization, recognition, facts, and events. These memories can be directly recalled, or “declared.” Spatial memories concern paths, layouts, routes, orientation, and environment.
Let’s say your friend is new to the town and asks you where the local grocery store is. Your declarative memory would recall the location itself (say, Publix), and your spatial memory would recall how to get there. You go there with your friend and help him find where different items are. Your declarative memory would recall if that Publix has certain items, brand names, etc., and your spatial memory would know how to navigate the store to find them.
Memory is so deeply rooted in the hippocampus that observing the decrease in its volume is used to diagnose the progress of Alzheimer’s disease. Depression is also linked to the hippocampus. In those who are diagnosed with depression, the hippocampus can shrink by up to 20 percent.
We are not born with as many neurons, or nerve cells, as we will have for the rest of our lives. The hippocampus is one of the few places in which adult neurogenesis takes place. Adult neurogenesis is the process of generating new neurons. These new neurons fit themselves in well with existing neural circuits. Many have grown up with the notion that whatever brain cells we were born with, those are all we have. This is technically wrong. It is important to note, however, that only the olfactory bulb and hippocampus participate in adult neurogenesis. As amazing as this is, we may ask ourselves why neurons don’t replicate in all parts of the brain. This mystery has yet to be solved.