A new study indicates that patients in the beginning stages of Alzheimer's might be able to regain memories previously thought to be permanently destroyed. Find out where "memory" is stored, and how it might come back if it's lost.
When an event happens, the brain pumps out a group of proteins. Those proteins create new synapses - connections between neurons. The forming connections can be disrupted, sometimes with something as simple as a bump on the head. This is why people who have been knocked out often don't remember the events leading up to their spell of unconsciousness. The long-term memory was never formed. Because serotonin aids in making these connections, diseases which cause a disruption in serotonin production, also can ruin someone's ability to make long-term memories.
There's another way to wipe out memories. Scientists observed the neurons of a snail, Aplysia, in a petri dish, then gave the neurons a dose of serotonin. The neurons had been "trained," in other words, they had formed a connection. The extra bit of serotonin was added as a way to retrain them, strengthening the connection. This is what would have happened, had the scientists not added a protein inhibitor. This inhibitor not only prevented the connections between the neurons from strengthening, but actually wiped out the synapses. The "memory" was gone.
According to the current theories about memory destruction, those synapses should have been gone forever. Memories are "stored" in the synapses. Destroy them, and the memories are wiped away. Any memories lost in the early stages of Alzheimer's, should also be gone forever. But a closer look at the neurons showed it wasn't that simple. Some of the synapses from the "training" were gone, but not all, and other synapses were destroyed as well. Damage had clearly been done, but the damage done didn't indicate the loss of a memory.
Outside of the petri dish, the scientists experimented on the snail by giving very mild shocks to its tail. The shocks were meant to make the snail retract in order to protect itself. Essentially, they were training it to have a defensive response. They were creating a long-term memory. Once the snail had been trained, they put it through the serotonin and protein-inhibitor combination they'd used to wipe out the synapses in the petri dish. Sure enough, the snail's memory of how and when to defend itself was wiped out.
Then the researchers gave the snail a few shocks, though not enough to spur a long-term memory. Despite the inadequacy of the training, the snail's response returned. If it had stored its memory in the synapses - which were destroyed - it would not have had the response. The researchers concluded that the snail's memories are stored somewhere else. And though it's a long jump from simple responses in a snail to memories in a human, if this research proves true, it's possible that patients with Alzheimer's, and other degenerative diseases, may regain memories they lost, if they get the right treatment.