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Neuro-Navigation: Hippocampus’s Role in Spatial Cognition

Author: Christine Chen

Editors: Sophia Chen, Hwi-On Lee, and Kevy Chen

Artist: Astrid Chen

How does an animal know where it is, where it wants to go, and how to navigate to its desired location without encountering any obstacles? Scientists have spent decades researching questions about the body’s ability to process spatial awareness. There are two main parts of the brain: one is tied to the action someone is currently doing, and the other is more “world-centered,” like finding your way through a new city. The latter part of the brain is centered around the hippocampus, tucked deep in the temporal lobe. The hippocampus aids in storing and using the information you collect to help you navigate the world.

Cells in the hippocampus fire signals based on where we are in the world, rather than just what we touch. Usually, nerve cells in the brain fire in response to events in their surroundings. For example, when someone pricks their finger, their muscles will move a certain way in reaction to the pain. These signals assist us in navigating our surroundings and help coordinate our actions. On the other hand, the hippocampus gives us a built-in GPS signal: a mental map of our environment, allowing long-term memory of places and routes without constant updates. 

To be more specific about the mechanisms that underlie this GPS signal, brain cells connect through recurrent collateral, a negative feedback system that stops the constant firing of signals, which aids the pattern completion process. This means that once you recall a few snippets of a memory, the entire memory comes back. All parts of the hippocampus receive signals from a part of the brain called the medial septum, which generates rhythmic brain activity, also known as beta oscillation. The oscillation is thought to help with processing new information, deciding whether to recall memories, and understanding the space around you. Additionally, the speed an animal moves is linked to the frequency and strength of this wave. This wave determines how other parts of the brain navigate, including place and grid cells which are essential for navigation.

There are many cells involved in spatial cognition. Place and grid cells, as well as head direction and boundary cells, are just a few of many. Place cells were first found in a rat’s hippocampus and dentate gyrus. When the rat is in a specific area, place cells start firing signals. Each cell has a “place field” where they create a visual map of the environment together. This map will stay the same even if colors or items change, to help you navigate your environment. For example, if you walked into a living room with blue tiles, you’d still recognize the room if the tiles were painted green. Unlike place cells, head direction (HD) cells fire based on which direction the rat faces, regardless of location. Each HD cell has a preferred direction, like how a compass tends to point north, creating a map based on the rat’s orientation. This helps the rat navigate through environments despite orientation. Again, going back to the living room example, if you stand in front of the TV, your HD cells would help you adjust to your surroundings versus if you were facing away. Grid cells help the brain track an animal’s movement and location more precisely, while boundary cells create a map of the environment’s edges. Aside from these examples, other cells are also involved in spatial mapping, responding to specific patterns or features of the environment. All these cells work together, allowing the brain to create a detailed and accurate map of an animal’s surroundings.

Besides an accurate map, memory is important in navigation—after all, animals have to remember where they left something and where to gather certain resources, such as food. This is considered long-term memory and is controlled by the medial temporal lobe. The hippocampus and the regions near the cortex are in this specific area and are crucial for remembering facts and events, otherwise known as declarative memory. There is still ongoing debate over what the hippocampus does differently from the rest of the medial temporal lobe. Many believe that the hippocampus helps us remember places, regardless of the viewpoint. Researchers have found evidence through a patient, H.M., who couldn’t remember where objects were placed due to a damaged hippocampus. Similarly, other patients with damage to the hippocampus also struggled with tasks involving spatial memory, such as finding their way around new places. The hippocampus has been known as the reason one has memories, so if there is damage, it’s not just spatial memory that is lost—it’s also forgetting words, facts, and faces. 

The hippocampus and its role in spatial cognition is essential to navigation because it maps out where we go and stores information about the places we go. Without it, people would never know where they were going, even if they walked the same route every day, or know where to get an item in a store without taking hours. 

 

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