Study: The reason some memories last longer than others

Clive Wearing is an exceptional musicologist; founder of the Europa Singers of London, a seasoned conductor and an accomplished tenor lay clerk of Westminster Cathedral.  Sadly, if you had any curiosities about his long, decorated career, Wearing himself couldn’t be of much assistance.

In 1985, at the height of his powers at BBC Radio 3, the ethnomusicology expert contracted a horrible infection that compromised his ability to make new memories as well as his ability to assess events that occurred or information that was learned after the onset of the illness; the worst case of anterograde and retrograde amnesia ever recorded.  “I have never seen a human being before, never had a dream or a thought. The brain has been totally inactive day and night the same,” Wearing once said of his condition.

He’s perpetually imprisoned in a hazy seven to 20 second loop-forgetting the name of foods before his first bite, forgetting questions in the middle of his response, greeting his wife with empathic confusion like it’s the first time they met-every time they meet. A mind stumbling through a succession of moments.

Somehow, certain inclinations persist. Even more than his vague and precarious awareness of fathering children, and being married, Wearing retains his ability to play the piano even if he couldn’t articulate how. Just last year Only Human produced a short documentary following up with Wearing, more than 20 years after his diagnosis. At one point he plays a piece for the filmmakers to all of their amazement. When they inquire after how’s he’s managed to do so without the ability to sustain memories for more than a collection of seconds he responds: “I’ve never heard a note since I’ve been ill. I don’t know what it’s like to play music.”

The illness responsible for Wearing’s degradation is herpesviral encephalitis, a herpes simplex virus that ravages the central nervous system, namely the hippocampus where memories are transferred and stored. Although Werning is no longer able to capitalize on episodic memory, he is still able to learn via procedural memory. Meaning if he were to hear information over and over again, eventually, he would secure the content but he wouldn’t remember where he’d heard it.

This alongside footage of Wearing dealing with his unfortunate circumstance submits a frustrating inquiry. Despite a short seven to 20-second reserve of memory, many aspects of his personality seem preserved. As his daughter notes, his sardonic sense of humor remains intact, as does his overall disposition. This suggests that there are some memories that are more integral to our character than others-neurologically speaking.

Encoding and synchrony

It’s long been understood, that our minds privilege some memories over others, and now researchers from the California Institute of Technology have successfully located the neurological mechanism that informs the process.  Procedural memory, like Wearing receiving information over and over again, works by reinforcing the encoding of the information being received. After examining mouse models,  Walter Gonzalez and his team discovered that strong memories are protected by a band of neurons firing in synchrony.

“Imagine you have a long and complicated story to tell. In order to preserve the story, you could tell it to five of your friends and then occasionally get together with all of them to re-tell the story and help each other fill in any gaps that an individual had forgotten. Additionally, each time you re-tell the story, you could bring new friends to learn and therefore help preserve it and strengthen the memory. In an analogous way, your own neurons help each other out to encode memories that will persist over time,” Gonzalez wrote.

In the study, a mouse was placed in a new enclosure, roughly five feet long and framed by white walls. Throughout the pen, were tracks and symbols signifying treats for the mice. When the animals first encountered these signals the researchers noted single-neuron activity, but the more familiar they became with their surroundings the higher the number of neurons, encoding their actions.

“For years, people have known that the more you practice an action, the better chance that you will remember it later,” explained co-author Carlos Lois to Science Daily.  “We now think that this is likely, because the more you practice an action, the higher the number of neurons that are encoding the action. The conventional theories about memory storage postulate that making a memory more stable requires the strengthening of the connections to an individual neuron. Our results suggest that increasing the number of neurons that encode the same memory enables the memory to persist for longer.”

This encouraging find adds a quantitative dimension to degenerative illnesses.  From dementia to infections that plague on the hippocampus, the study intimates a future wherein treatment can reinvigorate short and long term memory by recruiting a higher number of encoding neurons.

The study titled, Persistence of neuronal representations through time and damage in the hippocampus, was co-authored by Walter Gonzalez, Carlos Lois, and Anna Harutyunyan and was published in the journal Science.