Author: Karuna Meda
Institution: University of Pennsylvania
Memory recall involves shuffling through the innumerable scenes or scenarios stored in our brain. Inevitably, one memory leads to another, so instead of just recalling what movie you watched two weeks ago, you also remember a delicious (or unfortunately horrible) meal you had the very same day. Researchers led by Fred H. Gage at the Salk Institute of Biological Sciences found in their study, published on January 29th in Neuron, that new born neurons may have the ability to create time codes for memories that are formed around the same time, very much like a digital camera dates photos.
How do these "time codes" act during memory formation? Although there are many neural structures involved in memory consolidation, the hippocampus has been identified as preparing information for recall and then distributing it to the appropriate storage areas, like the temporal and frontal lobes of the brain. Incidentally, Gage and his team had initially set out to study the generation of new neurons in the "dendate gyrus" section of the hippocampus. In trying to identify the function of these new born neurons, methods for temporal information storage became apparent.
According to lead author, Brad Aimone,a graduate student in the Computational Neuroscience Program at the University of California, San Diego,at least 1% of all cells in the dendate gyrus are immature at any point in time. During the maturation process, the immature cells become less hyper-excitable, and begin to be integrated into the surrounding neuronal circuits. The researchers at the Salk Institute sought out all biological information from these new born brain cells, and fed it into a computer program, modeling the established circuitry of the dendate gyrus. The results showed that the highly active, newly spawned neurons, respond arbitrarily to all incoming information. Aimone explains, "The circuit in the dentate gyrus is designed to separate incoming memories into distinct events, a process called pattern separation, but immature cells get into the way by blurring the lines."
What is the point then of these excitable youngsters? Since these cells were active at the same time as mature neurons were forming memories, they are latently involved in memory recall. Gage says, "Our hypothesis suggests that cells that were easily excitable bystanders when the memory was formed are engaged as well, providing a hyperlink between all events that happened during their hyperactive youth."
What window of time do these time-codes work, and are there other hippocampal neurons besides those of the dendate gyrus that are involved? These questions will hopefully be answered by further studies. For now, the findings of this study provide a spring board for better understanding the temporal relationship between different memories.
Written by: Karuna Meda
Edited by: Jeff Kost (News and Features Editor) and Nira Datta (Professional Reviewer)
Published by: Hoi See Tsao