BOB HIRSHON (host):
Misdirecting fear. I’m Bob Hirshon and this is Science Update.
Imagine calmly staring down a loaded gun, but then running in terror from a tree. Something like that happened to mice in a recent experiment. University of Southern California neuroscientist Jean Shih and her colleagues engineered mice that lacked a key brain enzyme called monoamine oxidase A, which breaks down brain chemicals like dopamine and serotonin. Those mice became defensive around neutral objects like plastic bottles. Yet they were slightly insensitive to real threats, like the smell of a predator.
JEAN SHIH (University of Southern California):
These mice actually cannot differentiate. They don’t understand the threat.
Previous studies showed that the same enzyme deficiency made mice more aggressive. Now, it’s clear their defensive reactions are also impaired. Shih says the work could eventually shed light on human disorders, like autism and schizophrenia, that include defensive reactions to harmless stimuli. I’m Bob Hirshon for AAAS, the science society.