Professor Itzhak Fried, a neurosurgeon who led the study, says that his team have confirmed that the neurons that get excited during an experience are the same as those excited when a person remembers that experience.
This study attains significance because it may shed light on how memory recall works, and, in turn, help understand conditions like Alzheimer's disease.
"This is a rare opportunity to see how neurons, the basic units of cognition, work during the act of recall. It's unique because we're able to look at single cells in the brain when people spontaneously retrieve something from inside their memory without any cue from outside," says Prof. Fried, who is also a professor at the University of California Los Angeles (UCLA).
He reveals that the challenging study was conducted only on human subjects because other animals lack the ability to verbalize their memories.
"Taking a look at individual neurons can only be obtained under special circumstances. This is what we've managed to achieve," he says.
Prof. Fried has revealed that his team monitored the subjects' brain activity as electrodes recorded individual neurons, which enabled them to "see" real human memory recall in action, in real time.
The researchers located these neurons in the hippocampus-a sea horse-shaped brain area that is critical for memory formation and recall, and is affected in Alzheimer's patients.
It may be significant to note here that the hippocampus stores short-term "episodic" memories like what one ate for breakfast, and problems in this area in Alzheimer's patients explains why they become disoriented in familiar surroundings.
"This is the structure in which people lay down new memories and process them," says Prof. Fried, noting that in his recent study cells were very active in this area.
The researcher adds that the same cells spring back to life when this new memory is spontaneously recalled in experimental subjects.
During the study, the research team observed the neural activity in the brains of 13 epilepsy patients, as they watched clips from TV shows like Seinfeld and The Simpsons.
After a while, the researchers asked the participants to describe what they remembered from the video clips, and observed that exactly the same neurons that had fired while viewing a clip fired once again while the subject was recalling it.
Interestingly, the researchers even started predicting which clip the subjects would recall just by looking at the neurons that lit up seconds before the recall experience was vocalized.
Prof. Fried plans to continue research as he thinks that it may give science a better understanding of how memories are formed.
A research article describing his team's work has been published in the journal Science.