The human brain contains the hippocampus, a component of the limbic system. This small, curved area plays a significant role in our cognitive abilities, impacting our interaction with the world. Its workings continue to be a subject of research, revealing its influence on human experience.
Anatomy and Location
The hippocampus is situated deep within the medial temporal lobe of each cerebral hemisphere. Humans have two hippocampi. Its name, derived from the Greek word for “seahorse,” accurately describes its distinctive, curved shape. This structure is approximately five centimeters long, extending from the amygdala to the splenium of the corpus callosum, and is divided into a head, body, and tail. It is an inward fold of gray matter tissue within the parahippocampal gyrus.
The hippocampus is part of a larger group of structures called the hippocampal formation. This formation includes several sub-regions, such as the dentate gyrus, the hippocampus proper (which contains CA1, CA2, CA3, and CA4 fields), and the subiculum. These sub-regions have distinct cellular compositions and connectivities, contributing to the overall function of the hippocampus.
Primary Functions
The hippocampus plays a central role in several cognitive processes, particularly in the formation of new explicit memories. It consolidates information from short-term to long-term memory, acting as a temporary processing center before memories are stored elsewhere in the brain. This includes declarative memories, encompassing both episodic memories (personal experiences and events) and semantic memories (facts and general knowledge).
Beyond memory formation, the hippocampus is also involved in spatial navigation. It helps create and maintain cognitive maps, mental representations of our environment. Specialized neurons within the hippocampus, known as “place cells,” fire when an individual is in a specific location, aiding navigation. The hippocampus also contributes to various forms of learning, especially new information and associations.
Hippocampal Plasticity and Neurogenesis
The hippocampus exhibits adaptability through processes like synaptic plasticity, which is important for learning and memory. Synaptic plasticity refers to the ability of connections between neurons to strengthen or weaken over time in response to activity. This dynamic adjustment of neural connections allows the hippocampus to encode and store new information.
Adult hippocampal neurogenesis, the process by which new functional neurons are generated in the dentate gyrus throughout life, is also a feature. These newly formed neurons integrate into existing neural circuits and contribute to structural and functional plasticity. Adult neurogenesis plays a role in pattern separation, which is the ability to distinguish between similar memories, and may also influence mood regulation and learning.
Hippocampus and Cognitive Conditions
Damage or dysfunction of the hippocampus can impact cognitive health. One prominent impact is memory impairment, especially anterograde amnesia (inability to form new long-term memories). Issues with spatial memory and navigation are also commonly observed following hippocampal damage.
The hippocampus is vulnerable in neurodegenerative diseases like Alzheimer’s disease, often showing early damage and tissue loss. This atrophy contributes to the characteristic memory loss seen in the early stages of the disease.
Hippocampal function can also be affected by other conditions such as epilepsy, where seizures can lead to damage, and stroke. Changes in hippocampal volume or function have also been observed in mental health conditions like depression and post-traumatic stress disorder (PTSD).