Fear ‘off switch’ in mouse brains could lead to new treatments for anxiety disorders
Faced with a potential threat, a mouse will respond in one of three ways: either freezing (making it harder for the predator to detect it), ducking into the nearest shelter, or running for its life. Now, a team at Stanford University School of Medicine has identified two clusters of nerve cells in a mouse’s brain that control this response by sending signals to different regions. As similar circuitry is found in human brains, the discovery could potentially lead to new ways of treating phobias, anxiety disorders and post-traumatic stress disorder, they say.
The researchers placed mice into a specially designed tank that simulated the approach of a bird of prey by displaying an expanding dark disc above the mice’s heads, representing the shadow of a predator as it swooped overhead. By monitoring the mice’s brain activity as the ‘predator’ attacked, the researchers were able to determine that the ventral midline thalamus, or vMT, fired every time the mice sensed they were in danger. They then traced outputs from the vMT to the basolateral amygdala and the medial prefrontal cortex. Previous work has shown that the amygdala is involved with the processing of threat detection and fear, and the medial prefrontal cortex is associated with high-level cognitive control and anxiety.
They found that stimulating the amygdala increased the likelihood that the mice froze, while stimulating the medial prefrontal cortex led the mice to stand their ground and act in an uncharacteristically brave manner.
“You could hear their tails thumping against the side of the chamber,” said lead researcher Dr Andrew Huberman. “It’s the mouse equivalent of slapping and beating your chest and saying, ‘Okay, let’s fight!’.”
As human brains have a structure similar to the vMT, Huberman suspects that people with phobias, constant anxiety or PTSD, malfunctioning circuitry or traumatic episodes may benefit from therapies designed to damp down signalling in the region.
“This opens the door to future work on how to shift us from paralysis and fear to being able to confront challenges in ways that make our lives better,” said Huberman.