Researchers restore memories in amnesiac mice using light

MIT researchers have managed to recover so-called lost memories in mice with amnesia using light, and in doing so have raised questions about amnesia and memory storage. The method used to reactivate the memories was optogenetics, and involved adding proteins to neurons so that they can be activated using light. The experiment was conducted on mice, and the results indicate that "lost" memories do still exist, but access to them is essentially blocked and things like emotional triggers can't reactivate them.

A big source of debate when it comes to retrograde amnesia is whether it is caused by the inability for a memory to be stored, or by the memory being stored but the access to it being blocked. In the latter case, though it has not been the popular opinion, the memories could theoretically be reactivated if that block was removed or bypassed.

During the experiment, researchers used optogenetics to demonstrate that "memory engram cells" are subject to chemical changes. In one case, these changes are referred to as long-term potentiation and result in the synapses being strengthened, making way for the neuron groups to send signals between themselves. The result of this is learning (memory formation).

When the researchers blocked this chemical process from happening in the mice after they had formed a new memory, they effectively gave the mice amnesia, and weren't able to trigger the memory using an emotional trigger. This meant that while the memory still existed, blocking the protein synthesis meant that memory was "lost".

Using optogenetic tools, however, the researchers were able to reactivate the process and the mice, as far as their behavior could indicate, regained the memory that was lost.