What Is the Hippocampus? The 3 Main Functions of our Hippocampus

The hippocampus is a small part of the brain located in the medial temporal lobes (MTL), under the cerebral cortex. The hippocampus is an essential part of the brain’s limbic system, a group of brain structures in the cerebral cortex responsible for behavioral and emotional responses. Hippocampal function plays a critical role in learning, emotional responses, and memory formation and storage. The human brain contains two hippocampi, one on each side of the brain, located a few inches above each ear. The term “hippocampus”—derived from the Greek words hippo (meaning horse) and kampos (meaning monster)—translates to “seahorse,” a reference to its shape.

The hippocampus is a part of the limbic system that is closely related to memory. The integral functions of the hippocampus include:

• Influences memory formation: The hippocampal formation influences new memory formation and memory consolidation. This section of the brain also influences our ability to encode and retrieve information—where a short-term memory is registered before being transferred to long-term memory storage. The axons of the entorhinal cortex load information into the hippocampus, which sends signals to pyramidal cell neurons on the opposite end. These neurons are divided into two pathways: the polysynaptic pathway, the part of the hippocampus responsible for learning and memorizing facts and concepts, and the direct pathway, which is important for event recollection and spatial recognition.
• Informs behavioral responses: The hippocampus is connected to memory storage, and humans and other mammal brains draw from this stored information to influence our actions. Our previous experiences play a big part in how we form relationships and behave around others.
• Helps spatial cognition: In the direct pathway, the hippocampus can express spatial memory, like remembering driving routes or processing information about our location. The pyramidal cells in the hippocampus activate when we enter a familiar area, providing us with spatial navigation—the ability to navigate a place we’ve been before.

Damage, impairment, or underdevelopment of the human hippocampus can lead to many brain disorders, such as:

1. 1. Alzheimer’s disease: In people with Alzheimer’s, neurogenesis (creation of new neurons) is inhibited, and important cells and connections die off, leading to memory loss and impairment, and other mental dysfunctions.
2. 2. Amnesia: Damage to the hippocampus can impact a person’s ability to recall explicit memories such as names, dates, and events and affect their ability to imagine future experiences, also called anterograde amnesia.
3. 3. Epilepsy: Researchers discovered that between 50 and 75 percent of epileptic people who received autopsies post-mortem had damaged hippocampi. While advancements in neuroscience have led to important revelations regarding epilepsy, scientists are unsure whether epileptic seizures are the cause or effect of hippocampal damage.
4. 4. Schizophrenia: Abnormal structure, reduction in the size of the brain and hippocampal neurons, and decreased expression of essential genes and proteins have been observed in those with schizophrenia.
5. 5. Depression: People with depression are more likely to have a smaller sized hippocampus, along with a reduction in the size of the cornu ammonis, dentate gyrus, and subiculum, which are key subdivisions of the hippocampus structure.
6. 6. Post-traumatic stress disorder: Post-traumatic stress disorder (PTSD) is closely related to a person’s memory and experience of a traumatic event. Individuals with PTSD may not recall certain traumatic moments of their past or find that their memories of trauma are ever-present. This constant stress triggers the release of cortisol—the “fight or flight” hormone that signals to the body that we are in danger. High levels of cortisol can adversely affect the hippocampus.

Stress has one of the most significant impacts on the hippocampus’s plasticity, making this brain region vulnerable to the effects of hormones that modulate the formation of synapses and dendrites, which can cause abnormal connections and alter behavior. When we are stressed, our bodies produce high cortisol levels, triggering the immune system to release inflammatory chemicals, causing lower serotonin production and higher glutamate production, which can cause brain cell degradation over time.

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