Researchers at the National Institutes of Health were able to monitor brains replaying memories that involved the electrical activity of thousands of neurons. The visuals show the firing patterns of the cells performed when patients learned a world pair and were asked to remember it.
Kareem Zaghloul, a neurosurgeon at the NIH’s National Institute of Neurological Disorders and Stroke, said “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.”
The study's aim was to originally study patients with drug-resistant epilepsy. The patients had surgically implanted electrodes that were made to monitor brain activity. Thanks to these electrodes, the team successfully recorded the electrical currents of the patients.
The researchers managed to record the activity used to store memories of past experiences, which are called "episodic memories." This type of memory is stored in the brain and replayed when something triggers their recall.
Previous studies done on rodents showed that the rodent brain had a unique way of storing memories through neuronal firing sequences. Alex Vaz, a bioengineer from Zaghoul’s team, said, “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.”
The study was quite straightforward: the patients were asked to sit in front of a screen and learn unique word pairs, such as "cake" and "fox". The numerous experiments showed the unique firing patterns of individual brain cells that were associated with learning each new pattern in the brain's language center, anterior temporal lobe.
Moreover, when the patient was shown one of the words, a similar firing pattern replayed itself, just milliseconds before the patient recalled the paired word.
In the light of the results, Dr. Zaghloud said, “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."
The experiment supports the idea that the memories are possible thanks to a coordinated replay of neuronal firing patterns in the brain. Understanding how we form and retrieve memories can enable us to understand ourselves better, and give us power over our brains.