A study conducted by a team of medical scientists at MIT revealed the brain's circuitry links positive or negative emotions to a memory.

Moreover, scientists were able to reverse the memory-emotion association.

The findings demonstrated that a circuit of neurons connecting two regions of the brain (the hippocampus and the amygdala) play a critical role in associating emotion to a memory.

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Researchers found they could reverse the emotional association of specific memories by manipulating brain cells with "optogenetics," a technique that uses light to control neuron activity.

The finding could help in the creation of new drugs to help treat conditions such as post-traumatic stress disorder, depression or anxiety, researchers say.

"In the future, one may be able to develop methods that help people to remember positive memories more strongly than negative ones," says author Susumu Tonegawa of the Picower Professor of Biology and Neuroscience and director of the RIKEN-MIT Center for Neural Circuit Genetics at MIT's Picower Institute for Learning and Memory. 

With regard to their storage in the brain, memories are extremely complex. Different aspects are stored in different brain regions.

A memory's context, including information such as location, is stored in cells of the hippocampus. Emotions assigned to that memory are found in the amygdala.

The experiment involved male mice being conditioned with negative memories via mild electrical shocks and positive ones though interaction with females. Memories associated with context here found in the dentate gyrus, a subsection of the hippocampus.

Two days after their conditioning, the mice were let loose in an arena of two zones.

Researchers noted what side the mice found more comfortable, and then began stimulating the dentate gyrus cells with light as the mice wandered around the arena.

Mice conditioned with fear received memory stimulation whenever they were on the side they naturally preferred, and they soon began avoiding that area.

Mice with happy memories received stimulation when they wandered into the area they preferred less, and they ended up feeling better about that location and spent more time there.

When the protocols were reversed, a reverse result occurred

The study published in the Aug. 27 issue of Nature is already being praised by neuroscientists.

The research builds on existing data that shows memory is malleable.

Health professionals working with mental trauma patients have been able to lessen the emotional impact of certain events. The physiological aspect of emotion-memory association, however, have not been identified.

TagsMemory association, anxiety, depression, post-traumatic stress discorder, brain, MIT