Our brains replay memories like musical notes on a record

There is perhaps nothing more valuable than one’s memories. They define us, shape us, and push us forward. It isn’t a stretch to say that an individual is nothing more than the summation of his or her past experiences and lessons learned. 

For all of the groundbreaking discoveries and advancements in the medical and neurological fields over the past few decades, there is still a whole lot we don’t understand about the human mind and how our memories function. A new study, though, is offering a glimpse into how our minds recall and replay past events.

Our brains appear to store memories within “neuronal firing patterns” that repeat themselves within fractions of a second before we remember a past event or piece of information. These patterns first appeared when participants were taught something new, and then reappeared over and over again whenever the participants recalled said information. 

Just like grooves on an LP, it appears that our minds store memories within set neuronal behaviors that activate whenever we call upon them. In other instances, these memories can be activated involuntarily as well.

The research team, from the National Institute of Health, made these discoveries by monitoring the electrical activity of thousands of brain cells (neurons) in real-time while epilepsy patients were taught a word pair and then asked to recall what they had been taught.

So, the next you’re struggling to remember something specific, it is essentially like the memory record in your mind has caught a snag.

“Memory plays a crucial role in our lives. Just as musical notes are recorded as grooves on a record, it appears that our brains store memories in neural firing patterns that can be replayed over and over again,” says senior study author Kareem Zaghloul, M.D., Ph.D., a neurosurgeon-researcher at the NIH’s National Institute of Neurological Disorders and Stroke (NINDS), in a press release.

These epilepsy patients had been fitted with brain monitoring equipment for a reason entirely separate from studying memory; researchers were hoping to identify the source of their seizures within their brains. Still, the real-time electrical monitoring that had been set up represented a unique opportunity to study how our brains playback memories. More specifically, they monitored their episodic memory, or the ability to recall past experiences.

The basis for this research can be traced all the way back to another epilepsy patient way back in 1957. This patient referred to as HM, lost the ability to form new memories after a portion of his brain was removed to stop his seizures. This was modern medicine’s first indicator that our memories are stored within specific neural regions. 

Since then, a variety of research has indicated that our episodic memories can be activated by environmental cues like smells or sounds. We’ve all experienced it; hearing a certain song brings us back to a point in time, or the smell of a specific food reminds us of grandma’s home-cooked meals.

Incredibly, the idea of involuntary memory was first popularized in the early 20th century by famed French writer Marcel Proust. Proust used the premise of specific smells, locations, and sounds invoking memories in his literary classic In Search Of Lost Time, first published in 1913. 

In light of this new study’s findings, it stands to reason that these environmental cues serve to jumpstart the neuronal memory recordings in our minds, oftentimes involuntarily jumpstarting the “music,” so to speak.

Moving forward in time to more recent decades, rodent studies over the past 20 years had suggested that the mind stores memories within individual neuronal firing behaviors. So, while these findings aren’t completely without precedent, they nonetheless confirm what had only been hinted at previously.

“We thought that if we looked carefully at the data we had been collecting from patients we might be able to find a link between memory and neuronal firing patterns in humans that is similar to that seen in rodents,” comments Alex P. Vaz, B.S., an M.D., Ph.D. student at Duke University.

For this research, the epilepsy patients were asked to sit in front of a screen and learn various word pairs, like “cake” and “fox.” While this was happening the neural activity within their anterior temporal lobes was being monitored. This area of the brain is considered the language center. For each new word pairing learned, monitored brains displayed new, entirely unique neuronal firing patterns. Later on, when a patient was shown the word “cake,” those some neuronal patterns were repeated milliseconds before the individual correctly recalled “fox.”

“These results suggest that our brains may use distinct sequences of neural spiking activity to store memories and then replay them when we remember a past experience,” Dr. Zaghloul comments.

All in all, this study represents another piece of the puzzle when it comes to understanding the complexity of our minds. Somewhere between those neuronal patterns and electrical signals resides the very foundation for human consciousness and identity.

“Our results support the idea that memories involve coordinated replay of neuronal firing patterns throughout the brain,” Dr. Zaghloul concludes. “Studying how we form and retrieve memories may not only help us understand ourselves but also how neuronal circuits break down in memory disorders.”

The full study can be found here, published in Science.