CAMBRIDGE, Mass., May 29 (UPI) -- Using mice in a lab, researchers have shown that a memory "lost" to amnesia may actually be blocked from retrieval rather than excised from the brain.
Researchers found that when blocking protein synthesis within a group of cells in the hippocampus they were able to prevent mice from recalling a trained memory of being shocked when put inside a specific cage. Once the synthesis was permitted to happen again, the mice recalled why they feared the cage where they'd previously been shocked.
"The majority of researchers have favored the storage theory, but we have shown in this paper that this majority theory is probably wrong," said Susumu Tonegawa, the Picower Professor in MIT's Department of Biology and director of the RIKEN-MIT Center at the Picower Institute for Learning and Memory, in a press release. "Amnesia is a problem of retrieval impairment."
Tonegawa had previously used optogenetics, a method of controlling brain activity using light, to prove the existence of "memory engram cells." These cells synthesize proteins when the brain is recalling memories.
In the new study, researchers trained mice to expect an electric shock when they were placed in a specific cage. They then used a chemical called anisomycin which blocks protein synthesis in brain neurons to keep the mice from recalling their memory of the cage. Once the memory had been blocked, the researchers used light to reactivate the neurons and found the mice appeared to recall the entire memory.
"So even though the engram cells are there, without protein synthesis those cell synapses are not strengthened, and the memory is lost," Tonegawa says.
The study is published in Science.