A groundbreaking study on sleep, memory and the brain has just been completed by Karim Benchenane and his colleagues at the Industrial Physics and Chemistry Higher Educational Institution in Paris, France. Building on the discovery that won them a Nobel prize last year, the group has successfully created false memories into the minds of sleeping mice, spurring hopes that the same method might someday be used to assist humans who suffer from memory problems or who have lived through traumatic events.
Bechenane’s previous work and uncovered and identified individual cells in lab animals’ brains that are tied to a specific place, and that allow the formulation of internal maps. Using that information along with the knowledge that during sleep, the brain replays the activities that were experienced during the day in order to help it learn and remember, the researchers were able to stimulate specific brain areas while the brain was rehearsing what it had encountered and manipulate the information.
The process was accomplished utilizing electrodes that tracked the activities of the mice’s place cells during the day, as they encountered and explored an area that was previously unknown to them. By pinpointing the individual cell that was stimulated in a specific location, they identified that location’s place cell. Then when the mouse was sleeping they again monitored brain activity and when that place cell fired, a separate electrode stimulated the area of the animals’ brain that is associated with reward. When the mice woke up the next day the researchers released them back into the area that they had explored the previous day and the mice immediately went to the specific area that was associated with the place cell. The researchers had created a false memory of having received a reward in that particular spot by stimulating that part of the brain.
The research represents a first in science – though previous studies have been able to create subconscious associations, such as associating a noxious smell with a negative behavior in order to modify the behavior – this is the only time that a conscious memory has been created.
The proof of this lies in the behavior that the mice would have displayed without the reward center of the brain being stimulated. Normally when mice have been exposed to a new location, when reintroduced to it the next day after sleeping they would meander around the entire location again. But because the brain had registered a reward in association with the place cell, “The mouse develops a goal-directed behavior to go to that place,” says Benchenane. “It proves that it’s not an automatic behavior. What we create is an association between a particular place and a reward that can be consciously accessed by the mouse.”
Neuroscientist Neil Burgess of University College London explains why this research is so important. “The mouse is remembering enough abstract information to think ‘I want to go to a certain place,’ and go there when it wakes up. It’s a bigger breakthrough because it really does show what the man in the street would call a memory – the ability to bring to mind abstract knowledge which can guide behavior in a directed way.”
The success of the experiment is remarkable, but according to Benchenane, it only goes so far. He does not believe that there are a wide range of memories that can be implanted – for example, a new skill could not be created. By the same token, the research does provide a tremendous roadmap for the importance of individual cells within the brain to accomplishing or learning specific things, and that may be able to be utilized in a number of ways. “Even when those place cells fire in sleep, they still convey spatial information,” he says. That provides evidence that when you’ve got activation of place cells during the consolidation of memories in sleep, you’ve got consolidation of the spatial information.” He hopes that the combination of what his experiments have demonstrated will allow people’s traumatic memories to be modified in a positive way.
Memory plays an important role in many brain functions beyond learning, and has been closely tied to a number of mental disorders. For that reason, Loren Frank of the University of California is optimistic about the uses of this research. “I think this is a really important step towards helping people with memory impairments or depression. It is surprising to me how many neurological and psychiatric illnesses have something to do with memory, including schizophrenia and obsessive compulsive disorder.” He adds, “In principle, you could selectively change brain processing during sleep to soften memories or change their emotional content.”
Beyond those remarkable applications, people may wonder whether there are other uses for the discovery, such as making somebody have a positive impression of a person who they had previously disliked. After all, the idea behind Benchenane’s discovery is attaching good thoughts to existing memories, and therapeutically to those suffering from traumatic memories. The researcher said, “If you can identify where in the brain a person is reactivating a phobia-associated experience, you might be able to create a positive association.”
Since other researchers have found that there are single neurons that represent specific people in our brains, the theory that a neuron representing a person could be watched and a reward stimulus could be provided when it fires does not seem so far-fetched. It does, however, lead to ethical questions. Neil Burgess says, “The fact that you can do it during sleep is a bit worrying, in that it implies that you could make somebody want something even if they didn’t really.”
Speaking to these fears, Loren Frank reminds us that the experiment worked with existing memories, and that new memories can’t be created – existing memories can only be improved upon. “It’s not like they have created a whole new space that the animal is exploring in its head,” he says.