“MANIPULATING MEMORIES by tinkering with brain cells is becoming routine in neuroscience labs. Last year, one team of researchers used a technique called optogenetics to label the cells encoding fearful memories in the mouse brain and to switch the memories on and off, and another used it to identify the cells encoding positive and negative emotional memories, so that they could convert positive memories into negative ones, and vice versa.”
https://www.theguardian.com/science/neurophilosophy/2015/mar/09/false-memories-implanted-into-the-brains-of-sleeping-mice