Hippocampal volume refers to the overall size of the hippocampus, a brain structure below the cerebral cortex of the brain. The hippocampus is just one part of the limbic system, but it is important in processing information and forming memories, organizing information, and concentration. Various cognitive functions depend on the hippocampus, and the health of the structure is determined by analyzing its volume. Low volume or volumetric decreases can signify significant problems or be caused by a variety of factors.
Physicians use magnetic resonance imaging (MRI) scans to measure hippocampal volume. People with post-traumatic stress disorder (PTSD) often have a reduced volume of the hippocampus, especially in chronic forms of the condition. A smaller size of the structure to begin with could be a risk factor for PTSD because the hippocampus helps to evaluate the environment and determine things such as safety. It also helps to regulate cortisol, a hormone related to stress. Animal studies have also found that stress can trigger atrophy in the hippocampus, leading scientists to think that chronic PTSD can affect hippocampal volume.
Various diseases can have an effect as well. People with Alzheimer’s disease show decreases in hippocampal volume. The volume also decreases with age, and effects how information can be retained when there is a delay in retrieving it. Long term memory can be retrieved regardless of the state of the hippocampus, meaning it is maintained by other areas of the brain. Patients can immediately recall details and have trouble with retaining them after a delay, so recalling something right away and memorizing it for later retrieval are controlled by different areas of the brain.
Inside the hippocampus there are three pathways that are connected into a loop, called a trisynaptic circuit. Nearby structures transmit signals into it and are processed and transformed into other signals that are returned to the same areas. The idea that the hippocampus computes information makes it an important area to study when hippocampal volume is thought to be decreased. If the processing of brain signals is affected, this can affect long and short-term memory, spatial navigation, and perception of the surrounding environment.
Smaller hippocampal volume is a sign of or risk factor for conditions such as PTSD and Alzheimer’s disease. People with a larger hippocampus have shown faster recovery from post-traumatic stress. Whether hippocampal volume is affected by the outside environment or initially impacts the brain’s response are debated, but the hippocampus plays a vital role in cognition and the presence of various conditions.