7.19 : Role of Hippocampus in Memory

The hippocampus, a critical brain structure, plays an essential role in memory processing, particularly in the formation and retrieval of memory. This small, seahorse-shaped region is located within the medial temporal lobe, with one hippocampus in each brain hemisphere. Experimental studies involving lesions in the hippocampi of rats have demonstrated significant impairments in tasks such as object recognition and maze navigation, indicating the hippocampus involvement in both recognition and spatial memory.

One of the hippocampus primary functions is consolidating new memories. This process involves transferring information from short-term to long-term memory storage, allowing for the creation of lasting memories. The hippocampus sends memory-related information to other brain regions, processing and integrating it with existing memories.

The famous case of Henry Molaison (also referred to as H.M.), who underwent surgical removal of parts of his left and right temporal lobes, including most of the hippocampi, to alleviate severe seizures. After the surgery, his ability to form new declarative memories was significantly impaired. While he could remember events and information from before the procedure, he was unable to create new semantic knowledge or retain new experiences. Additionally, H.M. was unable to learn new spatial information, such as navigating unfamiliar environments, but he retained spatial memory of places from his childhood, like his home.

Research also supports the importance of the hippocampus in spatial memory. It shows that taxi drivers who frequently navigate complex environments have larger hippocampi than non-taxi drivers. This finding suggests that the hippocampus can undergo structural changes in response to increased demands on spatial navigation.