- The hippocampus is a small, seahorse-shaped structure located deep within the medial temporal lobe of the brain.
- It plays a central role in memory formation, particularly in the consolidation of declarative memories—those involving facts (semantic memory) and personal experiences (episodic memory).
- The hippocampus is part of the limbic system, a network of brain regions that supports emotion, behavior, motivation, and long-term memory. Although it does not store memories permanently, the hippocampus acts as a critical hub for organizing and linking new information before it is distributed to various regions of the neocortex for long-term storage.
- One of the hippocampus’s most well-documented functions is its role in episodic memory—the ability to recall specific experiences situated in time and place. This includes not only what happened, but also where and when it occurred. The hippocampus is essential for forming coherent memories from diverse sensory inputs and for enabling mental time travel, the ability to mentally revisit the past or imagine future events. Functional imaging studies have shown that the hippocampus becomes active during both memory encoding and retrieval, suggesting its involvement in the construction and reconstruction of experiences.
- Beyond memory, the hippocampus is also critically involved in spatial navigation and cognitive mapping. Research in both humans and animals has shown that specialized neurons in the hippocampus, known as place cells, become active when an individual occupies or thinks about a specific location. In concert with other cells like grid cells in the nearby entorhinal cortex, the hippocampus creates an internal representation of the external environment, which allows for orientation and navigation even in the absence of visual cues.
- Damage to the hippocampus, whether due to injury, stroke, oxygen deprivation, or neurodegenerative diseases such as Alzheimer’s disease, can result in severe memory impairments. One of the most famous cases is that of Henry Molaison (H.M.), who underwent bilateral removal of his hippocampi and subsequently lost the ability to form new declarative memories, although his procedural memory and previously acquired semantic knowledge remained largely intact. Such cases underscore the hippocampus’s critical role in memory consolidation, particularly for new information.
- Moreover, the hippocampus is highly sensitive to stress, aging, and neuroplasticity. Chronic stress and elevated cortisol levels can lead to shrinkage of the hippocampus, while positive experiences like learning, exercise, and adequate sleep have been shown to promote the growth of new neurons—a phenomenon known as adult hippocampal neurogenesis. This adaptability makes the hippocampus a key focus in research on cognitive resilience, memory disorders, and mental health conditions such as depression and PTSD.
