How mice’s brains respond to fear and “jump scares”

Researchers in the US have identified a previously unknown brain circuit that controls how mice respond to sudden threats and recover from fear. 

A jump scare is a sudden, intense stimulus that triggers an immediate fear reaction, like a loud noise or an unexpected shadow. In cinema, it’s used to shock viewers, but in real life, it mimics natural threats that activate the brain’s survival system. These fear responses, such as freezing or fleeing, evolved to protect animals (and humans) from danger. However, when this system becomes overactive, it can lead to anxiety or post-traumatic stress disorder (PTSD). 

A team at the University of Colorado Boulder exposed mice to a “looming shadow,”, simulating a predator’s approach. On the first day, the mice froze and hid. By the third day, after learning that the shadow posed no real threat, they adapted and stopped reacting. 

Using real-time brain imaging and optogenetics, the researchers pinpointed a zone in the midbrain (interpeduncular nucleus or IPN) as the centre of this process. When specific neurons in the IPN were active, the mice froze; when suppressed, they showed less fear. 

“The brain’s threat system is like an alarm. It needs to sound when danger is real, but it needs to shut off when it’s not,” said Elora Williams, first author of the study published in Nature. “Identifying the neuronal circuits underlying threat processing and adaptive learning is vital to understanding the neuropathology of anxiety and other stress-related conditions,” concluded Williams.