Mice can recall ‘lost’ memories

One of the earliest stages of Alzheimer's disease involves problems with episodic memory – the memories of certain events and their context, such as where something took place or who was there. One of the mysteries of the condition is whether this problem arises because the brain can no longer store new episodic memories, or if they are stored as normal but cannot be recalled. 

The researchers used a technique called optogenetics to try and find an answer to this question. Optogenetics involves using cells that have been specially tagged in way that means they respond to a special blue light. 

The researchers tagged brain cells in mice that are involved in the storage and retrieval of memories, meaning that they would respond to the special light. The mice also showed symptoms of Alzheimer's, gradually losing certain memories over time. However, after using the special light to activate the brain cells, the researchers found that the mice were able to recall things that they had previously forgotten.

This research offers evidence that memories that are 'lost' due to Alzheimer’s disease remain stored in the brain and that memory problems occur due to a loss of the ability to recall them. While the use of optogenetic techniques would not be possible in people, this research gives us valuable insight into the mechanisms that may lie behind memory loss in Alzheimer's. 

Dr Doug Brown, Director of Research and Development at Alzheimer's Society, said, 'One of the key issues with understanding memory loss in Alzheimer's is that we don’t know whether people are having problems storing memories or recalling them. This study in mice helps us to unpick the underlying processes and problems that lead to memory loss in the earliest stages of Alzheimer's disease – this new evidence suggests that memory recall is the issue.

'While interesting, the practicalities of this approach – using a special blue light to stimulate memory – means that we're still many years away from knowing if it would be possible to restore lost memories in people.'