Secrets of the Hippocampus: How Your Brain Uses Existing Patterns to Make New Memories

Making memories is no easy task. It requires the collective effort of many different mechanisms in many different areas of the brain, some known and others a mystery. Researchers from the Dragoi Lab in the Department of Psychiatry at the Yale School of Medicine wanted to unlock one more piece of the puzzle in how memories are encoded.


One of the areas where memories are encoded is the hippocampus, which is responsible for episodic memory. Episodic memory, otherwise known as the memory of events, requires the hippocampus to encode the information of the event, as well as the space, time, and other sequential information surrounding the event. In their recent study, Professor George Dragoi and postdoctoral scholars Kefei Liu and Jeremie Sibille found a method for how the brain rapidly encodes information of new, distinct episodes. Dragoi, Liu, and Sibille hypothesized that information is organized in the hippocampus, and the neurons that encode this information are organized in a similar way as vocabulary. Much like how vocabulary uses the same words in different combinations, they theorized that the hippocampus would use similar sequences to form a large repertoire of memories. Using minimally-invasive electrode implants on rats, the researchers tracked and studied the network activity of the brain to find combinations and patterns in memory encoding.


Dragoi explained that while the hippocampus is very good at rapid encoding, it is relatively limited in encoding extended experiences. “That poses a problem to an organ that is meant to do a lot of encoding, condensation, memorization, and recall over a lifetime,” said Dragoi.


Confirming their hypothesis, the researchers found patterns that confirmed a mechanism to encode extended experiences; they discovered that the hippocampus has 1043 possible neural combinations. This number seems large, but it shows that the hippocampus nonetheless has a limited number of combinations it can form. This supports the idea that the hippocampus is drawing on preexisting patterns to encode the new information, rather than creating something completely new.


These findings impact an ongoing debate in the scientific community over the existence of the preconfigured patterns. Contrary to prior theories, this research supports the concept that the hippocampus relies on preconfigured patterns and has limited capacity.


In the future, Dragoi hopes to use this research to further study the “vocabulary” of the brain and find out more about how memories are made.