For many people, forgetting memories is a natural part of growing older. However, there are people with memory loss that goes beyond just forgetting a name or two; sometimes these people forget how to do menial tasks or forget relationships they have all together. This type of excessive memory loss is devastating for people with who experience amnesia from traumatic events, or patients who are diagnosed with a neurodegenerative condition like Alzheimer’s, where the brain’s progressive deterioration leads to the affected person’s decreasing ability to remember things. The affected individual may constantly get frustrated or develop depression from their inability to remember things that are important to them such as their spouse’s name or their sibling’s birthday. The patient’s loved ones may go through the stress of taking care of the patient while watching them forget their memories. What if, however, this all can be reversed?
Researchers at the University of California, San Diego School of Medicine have been able to selectively activate and inactivate memories in rats by activating nerves within the brain at different frequencies, either strengthening or weakening synaptic (nerve cell) connections.
Using light-sensitive mice, the researchers undertook a two step process to teach the mice to fear the sight of a laser, which stimulated a group of nerves in the mice’s brains. First, they would play a tone while giving an electric shock to the mice’s feet simultaneously so the mice were conditioned–or learned–to be afraid of the tone. Once this fear was established, they then conditioned the mice to be afraid of a laser by pointing a laser at the mice while shocking them at the same time. The mice learned to associate the sight of a laser with the shock; this helped the mice create a memory of the experience, leading them to exhibit fear-based behaviors upon remembering the trauma of the laser and shock combination.
In order to inactivate that memory within the mice, low-frequency pulses of light were used to stimulate the same group of nerves as during conditioning. When they showed the mice the laser after these low-frequency pulses of lights, the mice no longer exhibited fear behaviors, leading the researchers to believe that the memory of the shock had been erased or suppressed.
However, when the mice were subjected to high-frequency pulses of light and then the laser, they once again responded with fear, suggesting that the memory had been reactivated or had returned.
This discovery has many clinical implications for humans. Being able to reactivate memories at will means that it may be possible to return lost memories to amnesiacs without having to wait for the memories to naturally return, if they return at all. For patients suffering from neurodegenerative conditions, they may be able to regain the memories that they have lost from the disease. It may even be able to work the opposite way for those who remember too much, particularly those who suffer from conditions like post-traumatic stress disorder. For patients with trauma, being able to suppress the memory whenever needed may help them speed through their recoveries.
While this research has brought scientists one step closer to possible therapies for many neurological disorders, applying this type of memory manipulation in clinical settings still has a long way to go.
Fox, R., Lin, J.Y., Malinow, R., Nabavi, S., Proulx, C.D., & Tsien, R.Y. (2014). Engineering a Memory with LTD and LTP. Nature. doi:10.1038/nature13294