When we go to a pal or go to the beach, our mind shops a brief-time period memory of the expertise in part of the brain referred to as the hippocampus. Those reminiscences are later "consolidated" - that is, transferred to a different a part of the mind for longer-time period storage. A brand new MIT examine of the neural circuits that underlie this process reveals, for the first time, that reminiscences are literally formed simultaneously in the hippocampus and the lengthy-time period storage location in the brain’s cortex. Nevertheless, the lengthy-time period reminiscences stay "silent" for about two weeks before reaching a mature state. "This and other findings in this paper provide a comprehensive circuit mechanism for consolidation of Memory Wave Workshop," says Susumu Tonegawa, the Picower Professor of Biology and Neuroscience, Memory Wave Workshop the director of the RIKEN-MIT Middle for Neural Circuit Genetics at the Picower Institute for Learning and Memory, and the study’s senior author. The findings, which seem in Science on April 6, could power some revision of the dominant models of how memory consolidation happens, the researchers say.

The paper’s lead authors are research scientist Takashi Kitamura, postdoc Sachie Ogawa, and graduate pupil Dheeraj Roy. Other authors are postdocs Teruhiro Okuyama and Mark Morrissey, technical affiliate Lillian Smith, and former postdoc Roger Redondo. Beginning in the 1950s, research of the famous amnesiac patient Henry Molaison, then known solely as Affected person H.M., revealed that the hippocampus is crucial for forming new long-term reminiscences. Molaison, whose hippocampus was damaged throughout an operation meant to help control his epileptic seizures, was now not able to store new reminiscences after the operation. However, he might still entry some memories that had been formed earlier than the surgery. This recommended that lengthy-term episodic recollections (recollections of particular events) are stored outdoors the hippocampus. Scientists believe these memories are saved within the neocortex, the part of the brain additionally accountable for cognitive features similar to consideration and planning. Neuroscientists have developed two major models to explain how recollections are transferred from short- to long-term memory.

The earliest, generally known as the usual model, proposes that short-term memories are initially formed and saved within the hippocampus solely, before being step by step transferred to lengthy-term storage within the neocortex and disappearing from the hippocampus. A more recent mannequin, the a number of hint model, means that traces of episodic reminiscences remain in the hippocampus. These traces might retailer particulars of the memory, whereas the extra basic outlines are saved within the neocortex. Until lately, there was no great way to check these theories. Most earlier research of memory had been based mostly on analyzing how harm to sure brain areas affects memories. However, in 2012, Tonegawa’s lab developed a option to label cells known as engram cells, which include particular memories. This allows the researchers to trace the circuits concerned in memory storage and retrieval. They also can artificially reactivate memories by using optogenetics, a method that permits them to turn goal cells on or off utilizing mild. In the brand new Science study, the researchers used this method to label memory cells in mice throughout a worry-conditioning occasion - that is, a mild electric shock delivered when the mouse is in a particular chamber.

Then, Memory Wave they could use light to artificially reactivate these memory cells at different instances and see if that reactivation provoked a behavioral response from the mice (freezing in place). The researchers might additionally determine which memory cells have been lively when the mice had been placed within the chamber the place the concern conditioning occurred, prompting them to naturally recall the memory. The researchers labeled memory cells in three parts of the mind: the hippocampus, the prefrontal cortex, and the basolateral amygdala, which stores memories’ emotional associations. Just in the future after the concern-conditioning occasion, the researchers found that reminiscences of the event had been being stored in engram cells in each the hippocampus and the prefrontal cortex. However, the engram cells within the prefrontal cortex have been "silent" - they might stimulate freezing behavior when artificially activated by mild, however they didn't hearth during natural memory recall. "Already the prefrontal cortex contained the particular memory information," Kitamura says. "This is opposite to the standard concept of memory consolidation, which says that you just regularly switch the reminiscences.