Much like using UV light to erase data from an EPROM, researchers from UC Davis have used light to erase specific memories in mice. [Kazumasa Tanaka, Brian Wiltgen and colleagues] used optogenetic techniques to test current ideas about memory retrieval. Optogenetics has been featured on Hackaday before. It is the use of light to control specific neurons (nerve cells) that have been genetically sensitized to light. By doing so, the effects can be seen in real-time.
For their research, [Kazumasa Tanaka, Brian Wiltgen and colleagues] created genetically altered mice whose activated neurons expressed GFP, a protein that fluoresces green. This allowed neurons to be easily located and track which ones responded to learning and memory stimuli. The neurons produced an additional protein that made it possible to “switch them off” in response to light. This enabled the researchers to determine which specific neurons are involved in the learning and memory pathways as well as study the behavior of the mouse when certain neurons were active or not.
Animal lovers may want to refrain from the following paragraph. The mice were subjected to mild electric shocks after being placed in a cage. They were trained so that when they were put in the cage again, they remembered the previous shock and would freeze in fear. However, when specific neurons in the hippocampus (a structure in the brain) were exposed to light transmitted through fiber optics (likely through a hole in each mouse’s skull), the mice happily scampered around the cage, no memory of the earlier shock to terrify them. The neurons that stored the memory of the shock had been “turned off” after the light exposure.
The researchers could see from this study that the mouse brain’s cortex, hippocampus, and amygdala are all connected and involved in learning, creating, and retrieving memories. Thus was long suspected but took optogenetics to clearly illustrate. We did not see any clear information on whether the “off” neurons were ever turned “on” again for the purposes of this study; it would have interesting to conclusively see if any of the fear response returned in the mice when this occurred.
As exciting as this research is, we’re still a long way off from scenarios like Eternal Sunshine of the Spotless Mind, the advent of neuralyzers, or treatment of memory disorders in humans using optogenetics. Still, we are impressed with the results and hope to see more studies about the science of memory in the future.
Here is a video explaining optogenetics: