Scientists have discovered a method to partially control a specific memory in mice by turning neurons in their brains on and off, according to a new study.
The work, conducted by researchers from Scripps Research Institute, advances understanding of how memories form and offers new insight into disorders such as schizophrenia and post-traumatic stress disorder
Though just an initial step, the researchers hope such work will eventually lead to better understanding of how memories form in the brain, and possibly even to ways to weaken harmful thoughts for those with conditions such as schizophrenia and post traumatic stress disorder.
Researchers have known for decades that stimulating various regions of the brain can trigger behaviours and even memories. But understanding the way these brain functions develop and occur normally - effectively how we become who we are - has been a much more complex goal.
"The question we're ultimately interested in is: How does the activity of the brain represent the world?" Mark Mayford, the study leader, said.
"Understanding all this will help us understand what goes wrong in situations where you have inappropriate perceptions. It can also tell us where the brain changes with learning," he said.
As a first step toward that end, the team set out to manipulate specific memories by inserting two genes into mice. One gene produces receptors that researchers can chemically trigger to activate a neuron.
They tied this gene to a natural gene that turns on only in active neurons, such as those involved in a particular memory as it forms, or as the memory is recalled. In other words, this technique allows the researchers to install on-off switches on only the neurons involved in the formation of specific memories.
For the study's main experiment, the team triggered the "on" switch in neurons active as mice were learning about a new environment, Box A, with distinct colours, smells and textures.
Next the team placed the mice in a second distinct environment-Box B-after giving them the chemical that would turn on the neurons associated with the memory for Box A.
They found that the mice behaved as if they were forming a sort of hybrid memory that was part Box A and part Box B.
The chemical switch needed to be turned on while the mice were in Box B for them to demonstrate signs of recognition. Alone neither being in Box B nor the chemical switch was effective in producing memory recall.
"We know from studies in both animals and humans that memories are not formed in isolation but are built up over years incorporating previously learned information.
"This study suggests that one way the brain performs this feat is to use the activity pattern of nerve cells from old memories and merge this with the activity produced during a new learning session," Mayford added.
The study has been recently published in the journal Science.