Amazing stuff!
"... Although the amygdala is widely considered the brain’s fear center, scientists have now discovered another area that responds to danger. The amygdalostriatal transition zone (ASt) is a small, long-overlooked region that sits alongside its more famous neighbor, and new experiments show that its neurons fire stronger and longer than those in the amygdala, which could explain why certain defensive behaviors persist. ..."
"Highlights
- Salk neuroscientists identify and characterize new region in the brain’s fear circuit called the amygdalostriatal transition zone (ASt)
- ASt neurons fire with more strength and for longer than the amygdala, which has historically been considered the brain’s fear center
- Findings explain why fear responses like freezing can last so long and point to therapeutic innovations for disorders like PTSD, anxiety
...
The ASt is tiny—it’s hard to reach, hard to study, and hard to distinguish from surrounding brain regions. Because of these challenges, the ASt has been relatively unexplored, leaving scientists unsure whether it is even a distinct brain region. This is the first landmark in the Salk paper: The researchers show that the mouse ASt is a distinct brain region, separate from the neighboring amygdala and striatum regions. ..."
From the highlights and abstract:
"Highlights
• ASt neurons have a unique genetic identity
• ASt neurons encode sustained responses to conditioned shock cues
• Activation of ASt neurons is sufficient to drive freezing and avoidance
• Drd2+ ASt neurons are necessary for expression of cued fear responses
Summary
To ensure survival, the brain must rapidly identify threats and maintain defensive behaviors for as long as danger is present. The amygdala has been studied as a key site for fear responses, but responses to threat cues in amygdala neurons are largely transient and shorter in duration than defensive responses observed.
Here, we present the amygdalostriatal transition zone (ASt) as a missing piece of the circuits mediating fear responses. Using single-nucleus RNA sequencing (snRNA-seq), we demonstrate that the ASt is genetically distinct from adjacent striatal and amygdalar structures.
In vivo electrophysiology and calcium imaging reveal that ASt neurons have robust, sustained responses to shock-predicting cues. Further, photostimulation of the ASt is sufficient to drive freezing and avoidance behaviors, and optogenetic inhibition experiments show that Drd2+ ASt neurons are necessary for cue-conditioned fear responses.
Our findings establish the ASt as a previously unappreciated yet critical structure for encoding learned associations and directing defensive behaviors."
Graphical abstract
Figure 1 The ASt is genetically distinct from the amygdala and striatum
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