EMBL scientists discover neural switch that controls fear
Fear can make you run, it can make you fight, and it can glue you to the spot. Scientists at the European Molecular Biology Laboratory (EMBL) in Monterotondo, Italy and GlaxoSmithKline in Verona, Italy, have identified not only the part of the brain but the specific type of neurons that determine how mice react to a frightening stimulus. In a study published today in Neuron, they combined pharmaceutical and genetic approaches with functional magnetic resonance imaging (fMRI) in mice. Their findings show that deciding whether or not to freeze to fear is a more complex task for our brains than we realised.
The scientists used an innovative technique to control the activity of specific cells in the brain of mice that were experiencing fear. The mice were genetically engineered so that only these cells contain a chemical receptor for a specific drug. When the scientists inject the mouse with that drug it acts on the receptor and blocks the electrical activity of those cells allowing the researchers to find out how these cells are involved in controlling fear. In this case, they used this pharmaco-genetic technique to turn off a set of neurons, called type I cells, in a region of the brain called the amygdala, which was known to be involved in responses to fear. To measure fear in mice, the EMBL scientists trained the mice to associate a sound with an unpleasant shock: when the mice heard the sound, they would freeze in fear.
"When we inhibited these neurons, I was not surprised to see that the mice stopped freezing because that is what the amygdala was thought to do. But we were very surprised when they did a lot of other things instead, like rearing and other risk-assessment behaviours," says Cornelius Gross, who led the research at EMBL, "it seemed that we were not blocking the fear, but just changing their responses from a passive to an active coping strategy. That is not at all what this part of the amygdala was thought to do."