MIT Neuroscientists Challenge Standard Model of Memory Consolidation

 

New research from MIT reveals that memories are formed simultaneously in the hippocampus and the long-term storage location in the brain’s cortex.

A region of the brain known as the hippocampus stores a short-term memory. Later, those memories are "consolidated," or moved to a different part of the brain for longer-term storage. 

For the first time, memories are actually formed simultaneously in the hippocampus and the long-term storage location in the brain's cortex, according to a new MIT study of the neural circuits that support this process. However, before reaching maturity, the long-term memories remain "silent" for approximately two weeks. 

S U S U M U, senior author of the study and P-I C O W E-R Professor of Biology and Neuroscience and director of the R-I K-E N-M I-T Center for Neural Circuit Genetics at the Institute for Learning and Memory, states, "This and other findings in this paper provide a comprehensive circuit mechanism for consolidation of memory". 

According to the researchers, the findings, which are published in the scientific journal Science, may necessitate some rethinking of existing theories regarding memory consolidation.

Research scientist Take S H-I, postdoc Sachie, and graduate student D H-E E-R A-G are the paper's primary authors. Postdocs T-E R U H-I R O and Mark Morrissey, a technical associate named Lillian Smith, and a former postdoc named Roger the other authors

Long-term Storage

Two major models have been developed by neuroscientists to explain how memories are transferred from short-term memory to long-term memory. According to the standard model, short-term memories are initially formed and stored in the hippocampus. Neocortex, which is also responsible for cognitive functions like attention and planning, is thought to store these memories

Theory Revision

Because memories are formed rapidly and simultaneously in the prefrontal cortex and the hippocampus on the day of training, the findings suggest that conventional theories of consolidation may not be accurate. 

"They're shaped equally, however, at that point, they go various ways from that point". According to Morrissey, "the hippocampus becomes weaker, and the prefrontal cortex becomes stronger". 

Paul Frank land, who was not a part of the study but is a principal investigator in the Neurobiology Laboratory at the Hospital for Sick Children in Toronto, says, "This paper clearly shows that engrams are formed in the prefrontal cortex from the start". It demonstrates that these circuits are simultaneously engaged, challenging the idea that the memory trace moves from the hippocampus to the cortex. The balance of which circuit is activated when a memory is recalled shifts as memories get older. 

To determine whether memories completely vanish from hippocampal cells or if only traces remain, additional research is required. The researchers are currently able to monitor encoding cells for approximately two weeks, but they are modifying their technology to function for a longer period of time. 

He asserts that he is of the opinion that some trace of memory may persist indefinitely in the hippocampus, storing details that are only occasionally retrieved. This silent engram may reactivate to differentiate between two episodes that are similar, and individuals can retrieve the detailed episodic memory, even at very distant time points, he states.

Additionally, the researchers intend to investigate the maturation of prefrontal cortex engrams in greater detail. Because blocking the circuit that connects the prefrontal cortex and the hippocampus prevented the cortical memory cells from maturing appropriately, this study already demonstrated that communication is essential between the two regions