London - Lost memories have been retrieved with the help of light in a study that could further the understanding and treatment of patients with severe amnesia following injury or disease.
Tests on laboratory mice showed that a lost memory is still stored within brain cells even though the animals have apparently lost their ability to retrieve it, scientists said.
Scientists have long debated the nature of amnesia, with many suggesting the problem is due to the storage of memory rather than the inability to retrieve it from the brain's long-term memory banks.
In a series of experiments on mice involving a technique called optogenetics - when light is used to activate specific nerve cells in the brain - researchers found that it was possible for the mice to remember a memory that had previously been lost. “Most researchers have favoured the storage theory, but we have shown in this [study] that this majority theory is probably wrong. Amnesia is a problem of retrieval impairment,” said Susumu Tonegawa, of the Massachusetts Institute of Technology in the US.
Retrograde amnesia, when memory loss occurs after traumatic injury, stress or diseases such as Alzheimer's, is probably caused by damage to the cells involving memory retrieval rather than memory storage, he added.
The study, published in the journal Science, found that the storage of memory is caused by building connections between nerves cells in the brain, while the ability to retrieve memory involves the strengthening of these connections, which can be blocked when the brain is damaged.
Memory researchers have previously suggested that memories are laid down in the brain by long-term physical or chemical changes to a specific network of nerve cells. If these cells are subsequently reactivated by a memory trigger, such as a smell or a sight for example, the entire memory can be recalled.
Dr Tonegawa said the study identified such a network of cells in the hippocampus area of the brain and that the connections between these cells were strengthened as part of the process of memory recall.
The Independent