The researchers had to figure out where the peptide was coming from after they found out that the amygdala did not produce neurotensin. When they scanned the brain, they found a lot of nerve cells in the thalamus.
The mice were taught to associate a tone with a treat or a shock. After reward learning and punishment learning, the levels of neurotensin in the amygdala went up and down. They were able to control how and when the thalamic neurons were altered. Knocking out the neurotensin genes made punishment learning stronger.
The assignment of valences to environmental cues promoted active behavioral responses to them. In threatening situations, the mice froze rather than running away when the researchers knocked out the thalamic neurons.
What would happen if an angry rhino charged you, for example? Tye said you would only care a little. In the future, your indifference in the moment would be recorded. She said that if you found yourself in a similar situation later in life, your memory wouldn't inspire you to flee.
Jeffrey Tasker said that the chances of an entire brain circuit shutting down is low. It is more likely that the mechanism will not work well if there is a problem. He said that it would be hard for someone to mistake a tiger for a love approach.
The brain likely has mechanisms that will kick in if the primary system fails. He said that this would be an interesting question to ask in the future.
Tasker said that one way to study defects in the system would be to look at people who don't feel fear. Unusual conditions and injuries can cause calcium deposits to form in the amygdala, which can make people less afraid.
The findings will help us understand the fear circuit and the role of the amygdala. She said that we are learning more about chemicals that are important in the brain.
There is a chance that the brain is pessimistic by default. Learning about punishments takes less time than learning about rewards.
The first time the mice were put into learning situations, they reacted negatively. They didn't know if the new associations would be positive or negative. According to the researchers, new stimuli are assigned a negative valence until their context can redeem them.
You are more responsive to negative experiences. If you almost get hit by a car, you will probably remember it for a long time, but if you eat a good meal, that memory is likely to disappear in a few days.
Ryan doesn't want to extend such interpretations to humans. He said that they were dealing with laboratory mice who were brought up in very poor environments.
It would be interesting to see if fear is the default state of the human brain in future experiments, or if it varies for different species, or even for individuals with different life experiences.
The thalamus and the amygdala need signals from other parts of the brain. She said it would be interesting to know which brain cells are sending signals.
According to a recent study, a single fear memory can be stored in more than one part of the brain. The memory is likely to affect which circuits are involved. For example, if you don't have a lot of emotion in your memories, it's less important to use neurotensin.
Tasker was very impressed by the clear-cut relationship found between a single molecule, a function and a behavior. Tasker said it is rare to find a one to one relationship between a signal and a behavior.
Drug targets for treating neurological disorders might be made possible by the crispness of the roles of neurotensin and the thal brain. If you can fix the assignment, you may be able to cure the disease.
It is not known if therapeutic drugs targeting neurotensin could change the nature of a memory. That is the hope, according to the man.
This is going to be difficult. Tasker said thatPeptides are difficult to work with because they don't cross the blood-brain barrier. He said that it is not impossible to develop targeted drugs.
There are important gaps in our understanding of how the brain works. It's not clear which receptors the neurotensin is binding to in the amygdala It will bother me until it's filled.
Hao Li, who was recently appointed as an assistant professor atNorthwestern University and is planning to explore some of these questions further in his new lab, said that too much is still unknown about how problematic valence assignments can drive anxiety, addiction or depression. There are many other brainpeptides that could be targets for interventions. We don't understand what they do. It wasn't clear whether the experience was good or bad, so he was curious to know how the brain would respond.
After he leaves for the night, the questions linger in his mind. He jokes with his friends that he has a network of cells in his brain that make him feel good or bad.
He said that it is clear that this is biology. It makes me feel better when I am depressed.
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