It's clear to everyone that many memories also have deep emotional connections. From the happiness and excitement we felt getting our first bike or at the birth of a child to the sadness and despair experienced over a breakup or the loss of a loved one, some memories remain colored by emotion long after they are formed.
What isn’t so clear — and what neuroscientists have been struggling to understand for some time — is exactly how our brains go about doing this.
In a new study from MIT, researchers show how brain circuits control the coloring of memories by emotional states. Even more promising is that they report actually reversing the emotional link of certain memories.
The researchers were able to manipulate specific brain circuits with a futuristic laboratory technique known as optogenetics. In optogenetics, scientists use light to activate and deactivate circuits in the brain.
The findings help to explain the success of behavior therapy in people with phobias or PTSD and may hint at potential treatments for emotion-based mental disorders including depression.
A circuit connecting two brain regions — the hippocampus and the amygdala — plays a crucial role in coloring memories with emotion, the researchers found. They hope that the findings may one day lead to drug targets that will help to treat conditions like post-traumatic stress disorder (PTSD).
“In the future, one may be able to develop methods that help people to remember positive memories more strongly than negative ones,” senior author Susumu Tonegawa said.
It is not known if the emotional color of a memory is fixed, or whether it could be altered. In other words, the memory itself might remain intact, but the emotions associated with it would change.
Mice were exposed to experiences designed to elicit either a fear or reward response, serving as examples of negatively- or positively-colored memory formation. The researchers observed which brain circuits were involved in these different memories.
Then they went a step further, attempting to switch the emotional coloring of a given memory from positive to negative and vice versa. For example, mice were subjected to a negative experience while the researchers used optogenetics to activate the brain circuit involved in the formation of positively-colored memories.
It was possible to change the emotional coloring of memories stored in the hippocampus, but not memories stored in the amygdala. These findings help to explain the success of behavior therapy in people with phobias or PTSD and may hint at potential treatments for emotion-based mental disorders including depression.
The work is published in Nature.