When the signals that generate fear are multi-sensory, you can smell fear.
The smell and heat of a fire give it away. A shadow is cast by an eagle as it flies overhead.
There is yet to be a neural pathway. There are two circuits that work together to strike fear into our brains.
The team of researchers suspected that the brain's fear center, the amygdala, was involved in the process.
They tested their hypothesis on genetically modified mice and found two different populations of CGRP in the brain and thalamus.
It's possible that this circuit could be involved in conditions such as headaches, anxiety, and depression.
The miniscope fitted to the mice allows scientists to track the activity of the CGRP neurons while the mouse is free roaming and responding to its environment.
A cotton top soaked in trimethylthiazoline, a component of fox feces that sparks fear, was one of the threats faced by the mice.
Half of the CGRP SPFp and CGRP PBel were recorded by the scientists.
When the mouse was confronted with threatening sounds, tastes, smells, sensations, and visual signals, most CGRP neurons increased their activity. The brain did not respond in a strong way to stimuli.
The brain pathway we discovered works like a central alarm system according to a neuroscience researcher.
The CGRP neurons are activated by negative sensory signals from all five senses.
The researchers wanted to know if the CGRP neurons were needed for threat perception. The fear response was not being triggered by the same neural cells.
When they silenced the CGRP neurons in mice, they ran the experiment again to see if they still showed the same pattern of fear.
The researchers found that mice that were silenced were less likely to respond to loud noises.
The researchers wrote in their paper that the results show that CGRP SPFp and CGRP PBel neurons are needed for behavioral responses to different threats.
The team showed that the CGRP neurons are needed for forming memories of threats.
Animals may be able to facilitate decision-making if threat signals are combined into a single area of the brain.
This research may inform treatments for medical conditions if the same CGRP neural circuit is found in humans.
"We haven't tested it yet, but it's possible that migraines could also cause these CGRP neurons in the thalamus and brainstem to be activated," says the co-first author of the study.
"Drugs that block CGRP have been used to treat migraines, so I'm hoping that our study can be an anchor to use this kind of drug in relief of threat memories in post-traumatic stress disorder, too."
The paper was published in a magazine.
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