It is sometimes said that you can smell fear, but in reality, the signals that produce fear are often multisensory.

For example, fire has heat, smoke and smell. An eagle flies overhead, casting shadows and flapping its wings as it swoops down.

If animals had a way to feed all sensory information from sight, smell, touch, taste and hearing into a single neural circuit to initiate a fear response in a part of the brain called the amygdala, it would help them survive. Threshold reached.

However, the existence of such neural pathways has not yet been established. A new study has provided strong evidence for two non-overlapping circuits that work together to impart fear to our brains.

The team of researchers behind the study began with the suspicion that neurons that utilize a molecule called calcitonin gene-related peptide (CGRP), along with the brain’s “fear center”, the amygdala, play a powerful role in the process. I got

Testing their hypothesis in transgenic mice, they found that there are two distinct populations of these CGRP neurons in the brainstem and thalamus, which connect to the animal’s amygdala.

Human neurons also express CGRP, suggesting that this circuit may be involved in conditions such as migraines, PTSD, and autism spectrum disorders.

The research team fitted mice with a small device for imaging calcium called a miniscope. This allows scientists to track the activity of her CGRP neurons while the mouse roams freely and reacts to its environment.

Mice were then faced with a threat stimulus that included a small foot shock. A burst sound that mimics thunder. An expanding and looming disc that simulates the rapid approach of a bird overhead.A cotton top soaked in trimethylthiazoline, a component of fox droppings Causes fear in rodents. Quinine solution with a bitter taste.

Scientists recorded the activity of 160 CGRP neurons, half of each of the two types.^SPFp and CGRP^{P Bell}.

They found that the activity of most CGRP neurons increased when mice faced threatening sounds, tastes, smells, sensations, and visual cues. I didn’t react so strongly.

“The brain pathways we discovered act like a central alarm system,” says Sung Han, a neurobiologist at the Salk Institute for Biology in California.

“We were excited to discover that CGRP neurons are activated by negative sensory cues from all five senses: sight, hearing, taste, smell and touch.”

The researchers wanted to confirm that these CGRP neurons are required for multisensory threat perception. In other words, no other neuron elicited the same fear response.

In mice, we silenced the CGRP neurons and ran the experiment again to see if the animals continued to exhibit the same pattern of fear behavior in response to scary stimuli.

Researchers found that mice that silenced these neurons were significantly less likely to respond to electric foot shocks and loud noises.

“These results confirm that CGRP^SPFp and CGRP^{P Bell} Neurons are required to mediate behavioral responses to a variety of multisensory threats,” the researchers wrote in their paper.

The team also used so-called Pavlovian learning experiments to demonstrate that these CGRP neurons are necessary for forming threat memories.

Focusing all these threat signals into one area of ​​the brain may help animals make decisions easier, the researchers conclude.

If this same CGRP neural circuit is found in humans, this research could help treat medical conditions.

“Migraines may also activate these CGRP neurons in the thalamus and brainstem, although we haven’t tested it yet,” says neuroscientist and co-first author Sukjae Joshua Kang. says.

“Since CGRP-blocking drugs have been used to treat migraine headaches, our study provides an anchor for the use of these drugs in alleviating threat memory in PTSD and sensory hypersensitivity in autism. I hope that

This paper cell report.