It has long been thought that when a memory is lost to a dementia causing disease, like Alzheimer’s, the part of the brain that held the memory is damaged or destroyed. New evidence suggests that the memory might still be there. It is the retrieval mechanism that has been lost. Scientists at MIT recently reported that memories that were thought to be erased from the brains of mice can be recovered. Investigations indicate that we may eventually find memories lost to Alzheimer’s disease and other dementia related diseases.

In a study led by neuroscientist Susumu Tonegawa,  mice were put into a cage and given a mild electric shock to their feet. When they were returned to that cage it was obvious that the mice all remembered the shock. Then  Alzheimer’s symptoms were experimentally  induced in half of the mice. This group of mice seemed to forget about the shocking.

Using a procedure called optogenetics (for details see the video above) the Alzheimer’s mice were able to reconnect with the lost memory, and became anxious once again when returned to the cage from which they had received the electric shock.

In a similar study, also conducted at MIT several years earlier, a team headed by Li-Huei Tsai trained mice in a water maze. The mice learned to find a hidden platform that allowed them to get out of the water. The memory of the platform was lost when Alzheimer’s like conditions were induced in the mice. Half of these mice were then given access to an enriched environment which contained a running wheel and various colorful toys and things to explore. The other half, the control group, were just put back in their cages. When the mice returned to the water maze, the control group performed no better than they did after having their memories wiped. Surprisingly, the group that spent time in the enriched environment were able to swim almost immediately to the platform. You can read more about this amazing study here.

Recent research indicates that memories lost to dementia may not actually be lost. It is possible that the neurons responsible for retrieving the memory have been damaged. There is evidence that the retrieval mechanism might be repaired; that we might find memories lost to Alzheimer’s and other neurological disorders.

It has been long thought that when memories are lost to a disease like Alzheimer’s, it is because the part of the brain that holds the memory is destroyed. This research may change that belief. The scientists involved in these studies theorize that the the retrieval mechanism in the mice’s brains was affected by the Alzheimer’s-mimicking procedure, not the memory itself. They speculate that much of the forgetfulness that often accompanies dementia may also be retrieval related, and that the retrieval mechanism just might be repairable. This suggests that, eventually, we may in fact be able to find memories lost to Alzheimer’s and other brain diseases.

Unfortunately, the optogenetic procedure used in the more recent study is invasive and can’t be used on people. If Tonegawa’s finding continue to hold promise it is likely that an alternate way to stimulate the neurons in humans will be developed. The earlier study is what really interests me, especially the conclusion that cognitive and sensory stimulation can do what the invasive optogenetic procedure did. Optogenetics is not available for the millions of people who have dementia, but enriched environments certainly are.