Neuroscientists can now switch memories from bad to good

By manipulating certain neurons in the brain, neuroscientists in the US can change the emotional association of a particular memory from bad to good in mice, and vice versa.

Give us another five minutes, will you? Researchers have created new positive memories in a male mouse by allowing him to spend some special time with two female mice.

Image: KPG Payless2/Shutterstock

Led by postdoctoral fellow Roger Redondo and graduate student Joshua Kim, a team from MIT has discovered a new technique for altering bad or fearful memories in the brains of mice by replacing them with new, pleasant memories.

To do so, they started off by establishing good and bad memories in the mice by prompting them to move into a certain area of their enclosure. Once they got there, they either received a treat, and so associated a good memory with that particular place, or they got a mild electric shock, which caused them to associate a bad memory with the place. The mice who got zapped did their best to avoid the area from that point on.

In order for the memories to be retained by each mouse, they needed to be encoded by two different areas of the brain. The memory of where the event happened - in this case that particular area in the enclosure - needs to be encoded by the brain’s hippocampus region, whereas the memory of whether the mouse experienced something good or something bad in this area - the emotional component of the memory - is encoded by the brain’s amygdala region. 

To alter the memory of a male mouse who got a shock when he ventured into the designated enclosure area, the researchers tried reactivating the neurons in the hippocampus that encoded where this memory was first established. They did this while he was having a very pleasant experience in the present - spending time with TWO female mice. Once the bad memory of the enclosure area was switched to a very pleasant memory, the researchers found that the male mouse spent a lot more time visiting it, probably hoping that his female friends would someday return. While the process sounds simple, achieving it was no small feat, as Greg Miller at Wired explains: