It is sometimes said that you can smell fear, when in fact, the cues that cause fear are often multi-sensory.
For example, fire has heat, smoke, and odor to make it go away. An eagle flying overhead casts a shadow and makes a fluttering sound as it swoops down.
It would be helpful for survival if animals had a way of feeding all the sensory information from sight, smell, touch, taste and hearing into a neural circuit that triggers a part of the brain called the amygdala so that a The times certainly trigger the fear response. reached the threshold.
Yet the existence of such a neural pathway has yet to be established. A new study has now provided strong evidence of two, non-overlapping circuits that work together to create fear in our brains.
The team of researchers behind the study began with suspicion that neurons using a molecule called calcitonin gene-related peptide (CGRP) played a strong role in the process, along with the brain’s ‘fear center’ – the amygdala.
Testing their hypothesis on genetically modified mice, they found two distinct populations of these CGRP neurons in the brainstem and thalamus that were connected to the animal’s amygdala.
Human neurons also express CGRP, so it is possible that this circuit is involved in conditions such as migraine, PTSD and autism spectrum disorder.
The researchers fitted the mice with a tiny device called a miniscope for calcium imaging, which allows scientists to track the activity of CGRP neurons while the mouse is moving freely and responding to its environment. .
The rats were then exposed to a threat stimulus, including a small blow to their leg; bursts of sound imitating a thunder explosion; an elongated, looming disc simulating the rapid approach of a bird’s upper back; a cotton top soaked in trimethylthiazolin, a component of fox feces which instills fear in rodents; and a solution of quinine, which has a bitter taste.
The scientists recorded the activity of 160 CGRP neurons, half of each of the two varieties: CGRP.spfp and CGRPpeebel,
They found that most CGRP neurons increased their activity when the mouse was faced with dangerous sounds, tastes, smells, sensations and visual cues. Neurons did not respond as strongly to control stimuli.
“The brain pathway we discovered acts like a central alarm system,” says Sung Han, a neurobiologist at the Salk Institute for Biological Studies in California.
“We were excited to find that CGRP neurons are activated by negative sensory signals from all five senses – sight, sound, taste, smell and touch.”
The researchers wanted to confirm that these CGRP neurons were essential for multi-sensory threat perception. In other words, that other neurons were not triggering the same fear response.
In rats they silenced CGRP neurons and re-run the experiment to see if the animals continued to show the same pattern of fear behavior in response to the fearful stimuli.
The researchers found that rats that had silenced these neurons were significantly less likely to respond to electric foot shocks or loud noises.
“These results indicate that CGRPspfp and CGRPpeebel Neurons are required to mediate behavioral responses to different sets of multi-sensory threats,” the researchers write in their paper.
The team also demonstrated that these CGRP neurons were essential for forming memories of threats using the so-called Pavlovian learning experiment.
By converting all of these danger signals into one area of the brain, it could help animals make decisions, the researchers concluded.
If the same CGRP neural circuit is found in humans, this research could inform the treatment of medical conditions.
“We haven’t tested this yet, but migraine may also activate these CGRP neurons in the thalamus and brainstem,” says co-first author Sukje Joshua Kang, a neuroscientist at the Salk Institute for Biological Studies.
“Drugs that block CGRP have been used to treat migraines, so I’m hoping that our study may be able to use this type of drug to help relieve danger memories in PTSD, or sensory hypersensitivity in autism.” To be an anchor.”
This letter was published in cell report.
(This story has not been edited by seemayo staff and is published from a rss feed)