Making Memories: A Look a 3 Recent Advances in how Memories are Formed
1. The journey to permanence of a memory.
What we’ve figured: A new memory, or engram, is encoded in short-term memory and then slowly over time gets converted or consolidated to long-term memory.
What’s being said now: A copy of that new memory is present in both the hippocampus, home to short-term memories, and the prefrontal cortex, home to long-term memories. A study published in April 2017 in Science gave mice shocks and showed that when short-term memory in the mice was switched off, the mice forgot about the shock. However, using optogenetics, if long-term memory was switched on the mice could remember the shocks, even with short-term memory still switched off. So the memory was there in the mice but it wasn’t used in the first two weeks unless artificially stimulated by the researchers. Other researchers have called this type of memory a silent engram. Although mice were used, it is believed the same thing happens in human memory formation.
2. The strength of a memory.
What we’ve figured: How well something is remembered is a result of how strong the connection is to that memory.
What’s being said now: It’s not just the strength of the memory but the state you are in when the memory is made. Research done at the University of Toronto shows that there are two important states that are inversely related to each other: novelty and familiarity. Novelty is good for memory formation but not for memory retrieval. Familiarity is good for recalling something but not good for encoding a strong memory. Therefore, different brain states can impact the formation and recall of memories. And it appears these brain states run on separate circuits. There are two theories for why the hippocampus would need two distinct pathways for memory formation and recall. Having these two circuits would help an animal first recall a memory and then, if there is new information to be added (i.e., novelty), formulate and update the memory accordingly. The other theory involves the creation of long-term stress responses. That is, experiencing the release of stress hormones a while after the memory of the stressful experience is created. This could be a way to more strongly remind us to be careful of or stay away from whatever it was that caused the stress.
3. The ability to remember the details of a memory.
What we’ve figured: That the parts of the brain associated with memory, primarily the hippocampus, have fully matured by the age of six.
What’s being said now: The hippocampus does not complete its maturation until adolescence, approximately age 14. Researchers collaborating from three different institutions have found that our ability to separate features of things so that they can be separately remembered as well as the ability to form, stabilize and retrieve memories is age-related. That is, remembering the super-fine details of something, not just the ability to remember it in general, matures over time.
