A neural switch for fear
When something frightens us, should we freeze, or should we investigate? Sarah Stanley describes how scientists from the European Molecular Biology Laboratory are probing the mysteries of the brain, seeking to understand our response to fear.Flee, fight or freeze? For an animal overcome with fear, that is the essential question. The answer often depends on the amygdala – a major emotion-processing hub nestled deep in the brain. In both mice and humans, it affects how we behave in response to certain types of fear, and helps to form long-term memories of frightening experiences. However, very little is known about how cells in the amygdala communicate with other brain cells to produce specific fear-induced behaviours.A recent study narrows this gap in knowledge, thanks to the innovative work of scientists at the European Molecular Biology Laboratoryw1 (EMBL) in Monterotondo, Italy, and GlaxoSmithKlinew2 in Verona, Italy. The scientists focused on one of many different types of fear processed by the amygdala. They used new techniques to understand the interactions between the areas of the brain involved in reactions to that specific type of fear. In the course of their work, they identified a switch that toggles between two different fear responses: freezing and, surprisingly, an alternative to the flee, fight or freeze options, known as active risk assessment. This active response involves behaviours like rearing, digging and exploring.Mice conditioned to associate a tone with an uncomfortable shock usually freeze in fear upon hearing the sound, even if it is not accompanied by discomfort. Neurons called type 1 cells, which are found in the amygdala, are known to control the freezing response. When type 1 cells are prevented from sending signals to other cells, mice no longer freeze in fear. But, it seems, type 1 neurons are more than just an on / off switch.Mice conditioned to associate a tone with an uncomfortable shock usually freeze in fear upon hearing the sound, even if it is not accompanied by discomfort. Neurons called type 1 cells, which are found in the amygdala, are known to control the freezing response. When type 1 cells are prevented from sending signals to other cells, mice no longer freeze in fear. But, it seems, type 1 neurons are more than just an on / off switch.