Memories are a strange, inexact phenomenon. Our memories frequently feel like a jumbled collage of moments and experiences that plays at random. We struggle to recall important facts or past events but will lay awake at night pondering mistakes from years ago. It can feel like there’s no rhyme or reason to what we can and can’t remember at any given moment, and for each memory, we recall there are hundreds more that have disappeared from our minds.
Think back to some of your clearest memories from childhood. Most of them are probably common, everyday occurrences; dinner with family trips to the store, playdates with other kids. Now, you obviously ate dinner with your family or went to the store countless times growing up, so why is it that we only remember a few select experiences? A new study from the University of California, San Diego is offering up an explanation.
Researchers have discovered that when neurons inside the hippocampus are firing at a high rate before one attempts to form a new memory, that person will be much more successful at encoding the memory and efficiently recalling it later on. Conversely, when hippocampal neurons are largely inactive, it’s much harder to form clear memories.
So, this all strongly indicates that our brains are much better at forming memories when they are “prepared.” On a more technical level, the study’s authors say that the hippocampus enters into a “ready-to-encode” mode that makes it easier to form lasting memories.
This is a huge discovery, but it also immediately begs the next logical question: how do we activate this ready-to-encode mode? As of now, the researchers are still unsure.
“A key question going forward is how to put our brains into ‘encoding mode’ when we wish to do so,” says lead study author John Wixted, professor of psychology at UC San Diego, in a university release.
“‘Encoding mode’,” professor Wixted explains, “is more than simply paying attention to the task at hand. It is paying attention to encoding, which selectively ramps up activity in the part of the brain that is the most important for making new memories: the hippocampus. Since we know, based on earlier research, that people can actively suppress memory formation, it might be possible for people to get their hippocampus ready to encode as well. But how one might go about doing that, we just don’t know yet.”
This research was conducted on a group of 34 epilepsy patients. Each patient had their neuronal activity scanned and recorded as they attempted to memorize and subsequently recognize a series of words. Participants were played or shown a series of words; at first, all of the words were new, but eventually, words started to be repeated. Patients were asked to identify repeated words.
While that was happening, researchers took note of the average number of times a neuron fired whenever a participant saw or heard a word, as well as neuronal activity right before another word appeared. Surprisingly, the firing of neurons when patients saw words didn’t have any effect on their memory. However, neuronal activity just before did make all the difference. If a person’s neurons were already active and firing before hearing or seeing a new word, they almost always remembered it.
“If a person’s hippocampal neurons were already firing above baseline when they saw or heard a word, their brain was more likely to successfully remember that word later,” says Stephen Goldinger, a professor of psychology at Arizona State University.
There are so many moments in life that seemingly never make it to our memories, while others fade away with time. The fact that so much of our lives become lost even to us seems cruel, but most simply assume our minds just can’t store everything. Perhaps that isn’t the case after all.
“We think new memories are created by sparse collections of active neurons, and these neurons get bundled together into a memory. This work suggests that when a lot of neurons are already firing at high levels, the neuronal selection process during memory formation works better,” professor Goldinger concludes.
The full study can be found here, published in Proceedings of the National Academy of Sciences.
John Anderer is a frequent contributor for Ladders News.