Even the best brains have imperfect memories. We often forget things, and many people even sometimes remember things that did not happen, which are known as false memories. While we know it is possible to implant such fabricated recollections into our minds merely through suggestion, scientists are now beginning to demonstrate it is also possible to do this with the aid of sophisticated technology, albeit in animals, not humans. Just last year, for example, researchers managed to make mice wrongly associate an environment with an unpleasant experience from a different place using a combination of gene editing and light stimulation of brain cells.
Now, taking this one step further, researchers from the French National Center for Scientific Research have successfully implanted artificial memories into the minds of snoozing mice, a first for neuroscience. What’s more, these bogus memories persisted and actually affected the animal’s behavior when they woke up. Alongside being a remarkable achievement, the study is helping further our understanding of the role played by sleep in memory consolidation and could maybe one day lead to the development of ways to make humans less susceptible to false memories, which can be a serious issue in criminal cases.
In order to trick the animals’ brains, the researchers inserted electrodes that were designed to target two different areas: a critical component of our reward system, the medial forebrain bundle (MFB), and part of our learning and memory hub, the hippocampus. More specifically, the part of the latter region they honed in on is known to contain neurons called place cells. These nerves, the discovery of which earned a Nobel Prize last year, are cells that become activated, or fire, when an animal is in a specific location in the environment, known as the place field. In combination with another type of neuron, these cells constitute our brain’s “inner GPS,” which is required for spatial navigation.
To identify these place cells, the researchers allowed the animals to explore their environment whilst recording neuronal activity. After picking out the cells that fired when a mouse entered a particular place field, the researchers began stimulating the MFB while these place cells were active during wakefulness. This led to the generation of a false positive association between a particular area and a reward, or pleasurable experience. Consequently, the mice spent significantly longer exploring these areas compared with control animals in which the neuronal stimulation was random.
Since it is known that neurons in the hippocampus replay the day’s experiences during sleep, the researchers continued to monitor brain activity whilst the animals were taking a kip. With the help of a brain-computer interface, the MFB was automatically stimulated whenever a specific place spontaneously cell fired. Once again, when the animals were awake, they spent up to five times longer exploring the area associated with the place cell activity compared with animals who had received random MFB stimulation, suggesting they had a conscious memory that some kind of reward was in this particular location.
Of course, since this technique involves brain implants, it is highly unlikely that it will be repeated in humans. Still, scientists are hopeful that the findings could represent an important step towards assisting people with certain memory problems or mental health disorders in which memory plays a role.