Bianca Silva, who carried out the work, said that they found that there seems to be a circuit for handling fear of predators – which has been described anatomically as a kind of defence circuit – but fear of members of the same species uses the reproductive circuit instead and fear of pain goes through yet another part of the brain.
Working in the lab of Cornelius Gross at European Molecular Biology Laboratory (EMBL), Silva exposed mice to three threats: another mouse (chosen for being particularly aggressive), a rat (the mouse’s natural predator) or a mild electric shock to the feet. The mice showed the same typical fearful behaviours – running away, freezing – in response to all threats, but their brains painted a different picture.
When the scientists mapped the brain activity of mice exposed to the aggressive mouse and the rat , they saw that different parts of a region called the ventromedial hypothalamus (VMH) ‘lit up’ depending on the threat.
Fear of the mouse seemed to activate the bottom and sides of the VMH, while fear of the rat seemed to be processed by the VMH’s central and upper areas. This was confirmed when the scientists used drugs to block only the neurons in those ‘rat fear’ areas: mice were no longer afraid of the rat, but were still afraid of the mouse, showing that mice need this brain circuit specifically to process fear of predators.
The human brain has similar circuits, and we too experience different kinds of fear, so the results hint at the possibility of developing more efficient treatments for specific phobias or panic attacks, by targeting only the relevant region of the brain. The study has bee published in journal Nature Neuroscience.