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How does the brain identify rewards and punishments?

The amygdala is a small, almond-shaped structure located deep within our brain’s temporal lobes, which plays a fundamental role in learning, remembering, triggering fight-or-flight responses, and promoting the release of a “feel-good” chemical called dopamine. Although scientists have studied this brain structure for decades, they have not yet reached a full understanding of how it functions.

Now, a team of researchers led by the Cold Spring Harbor Laboratory (CSHL) has made a series of discoveries that clarify how so-called somatostatin-expressing (Sst+) central amygdala (CeA) neurons help us learn about threats and rewards, and how they are related to dopamine. These findings could be of crucial importance in the future development of treatments for mental health issues such as anxiety disorders or drug addiction.

While scientists have previously assumed that the amygdala cannot distinguish between good and bad stimuli, a series of experiments on mice taught to associate specific sounds with particular rewards and punishments have shown that not only did the neurons respond differently to rewards versus punishments, but also responded differently to various types of rewards.

“This is entirely new to us. These neurons really care about the nature of each individual stimulus. It’s almost like a sensory area,” said study lead author Bo Li, a professor of Neuroscience at CSHL.

Moreover, since the mice’s brains fired more Sst+ CeA neurons after training, these neurons seem to be essential for learning. To test this hypothesis, the researchers inhibited Sst+ CeA neurons in some of the mice, and discovered that these animals were unable to associate sounds with rewards or punishments. In addition, normal dopamine neuron responses were also suppressed in these mice.

“We found those neurons are required for normal function for dopamine neurons, and therefore are important for reward learning. That is direct evidence of how CeA neurons regulate the function of dopamine neurons,” Li explained. 

In future research, the experts aim to examine more closely the relationship between Sst+ CeA neurons and addiction, which could potentially help devising better treatments. “Our study provides a basis for developing more specific ways to regulate these neurons in different disease conditions,” Li concluded.

The research is published in the journal Nature.

By Andrei Ionescu, Staff Writer

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