Memory manipulation is the stuff of science fiction and urban myths. At least it was until a series of experiments on mice have shown it is possible.
Last year I wrote about a study in which scientists used light to create and delete false memories of fear in mice. A different group used the same method to switch emotionally-charged memories from good to bad and vice versa in mice. This only worked for the memories contained in cells from a particular area of the brain called the hippocampus.
Now scientists have used cells in the same area of the brain to create false happy memories in sleeping mice. They did this by manipulating cells that encode the place part of a memory (imaginatively called place cells) in the hippocampus.
First the mice were allowed to explore a new area, which we can call the playground to make the rest of this explanation easier, and electrodes measured which place cell was activated while the mouse was in the playground ie which cell was encoding the memory of the playground. Then the mice were monitored while they were sleeping, and whenever this place cell fired, it caused a second electrode to stimulate another area of brain that normally lights up when the mouse is rewarded (called the medial forebrain bundle). So the mice formed a memory of being rewarded in the playground even though they never were. This experiment didn’t wake the animals up or change basic brain function during sleep. As a control the same experiment was done in awake mice. Afterwards both groups of mice went straight to the playground and spent 4-5 times as much time there as mice which did not have the rewarding electrode treatment. However this effect only worked for the first two visits to the playground then wore off as the mice realised there was no real reward.
While we sleep place cells replay memories to make them stronger – a process called consolidation. The point of this experiment was to show that place cells are essential to this process. However, what it also does, is show that it is relatively easy to create false memories in living animals which to me is pretty scary.
The Scientific Paper: