New neurological research has answered the question of whether amnesia is caused by damage to the specific brain cells that hold the lost memories, or if access to the memories in those cells are being blocked. And in the process, this research may have uncovered a way to recover memories that were previously lost.

Using a light-based therapy called optogenetics, a team at MIT’s RIKEN-MIT Center at the Picower Institute for Learning and Memory found that they could re-activate specific memories in mice that had previously been blocked using a protein synthesis-blocking therapy, via a compound called anisomycin. In doing so, they found that memories are stored in a circuit that encompasses multiple areas of the brain, meaning that if a memory is blocked by damage to one area of the brain, the memory itself might still be stored elsewhere, and not lost altogether.

RIKEN-MIT Center director and team leader, professor Susumu Tonegawa, elaborates: “If you test memory recall with natural recall triggers in an anisomycin-treated animal, it will be amnesiac, you cannot induce memory recall. But if you go directly to the putative engram-bearing cells and activate them with light, you can restore the memory, despite the fact that there has been no LTP.” (LTP, or "long-term potentiation", involves the strengthening of the brain’s synapses, the communicative structures between neurons.)

“We are proposing a new concept, in which there is an engram cell ensemble pathway, or circuit, for each memory,” Tonegawa says. “This circuit encompasses multiple brain areas and the engram cell ensembles in these areas are connected specifically for a particular memory.”

This could be a significant benefit to close encounter witnesses, who are often deeply troubled by whether or not their strange memories are of real events, or are somehow distorted or even artificially induced. In addition, the ‘missing time’ experience appears to involve completely lost memories of often large periods of time. The recovery of such memories would be a major advance.

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