Imagine star-shaped cells in your brain extending long, thin extensions to surround nearby neurons. These cells are called astrocytes. Scientists have long believed that astrocytes function primarily as caretakers, holding neurons together and keeping brain circuits running smoothly.
Now, new research is challenging that idea. These widely distributed “support cells” appear to be as important as neurons when it comes to the formation and control of fear memories.
“Astrocytes are intertwined between neurons in the brain, and it’s hard to imagine that they’re just there for housekeeping. We wanted to understand what astrocytes actually do, and how they shape neural activity in the process,” said Lindsay Halladay, an assistant professor in the University of Arizona’s Department of Neuroscience and one of the study’s senior authors.
Halladay’s team collaborated with scientists at the National Institutes of Health on this multi-institutional project, led by Andrew Holmes and Olena Bucaro of the Institute for Behavioral and Genomic Neuroscience.
Astrocytes help the brain learn and release fear
This study naturefocused on the amygdala, a key region involved in fear processing. Researchers found that astrocytes in this region play a direct role in how the brain learns what to fear, how to recall those memories, and, importantly, how to learn when those fears are no longer relevant.
“For the first time, we discovered that astrocytes encode and maintain neurofear signaling,” Professor Halladay said.
The findings challenge the long-held view that neurons are central to fear processing and suggest new ways to approach conditions such as post-traumatic stress disorder.
Observe the shape of fear in real time
To find out how fear memories develop, the researchers used a mouse model and closely tracked brain activity. With the help of fluorescent sensors, they were able to observe the astrocytes where fear memories are created and later recalled.
Astrocyte activity increased during learning and recall. As the fear memory gradually disappeared, the activity of these cells decreased. The researchers then changed the signals the astrocytes sent to nearby neurons. Strengthening these signals makes the fear memory more intense, while weakening them reduces the response.
These results indicate that astrocytes are not passive helpers. They actively shape how fear is stored and expressed in the brain.
Destroying astrocytes changes brain circuits
Changes in astrocyte activity also affected neuron behavior. When astrocyte signaling was disrupted, neurons struggled to form normal activity patterns associated with fear. This impaired the ability to send information about appropriate defensive responses to other parts of the brain.
The findings challenge the traditional neuron-focused view of fear and show that neurons do not act alone in the generation of fear memories.
Beyond the amygdala: the broader fear network
Astrocyte influence extended beyond the amygdala. Changes in their activity also affected how fear-related signals reach the prefrontal cortex, which is involved in decision-making.
This suggests that astrocytes not only help create fear memories, but also help guide how the brain uses those memories to choose appropriate responses in threatening situations.
New possibilities in the treatment of PTSD and anxiety disorders
Understanding the role of astrocytes could change the way scientists approach diseases associated with persistent fear, such as post-traumatic stress disorder, anxiety disorders, and phobias.
If astrocytes help control whether fear memories emerge or disappear, future treatments could target these cells alongside neurons to improve outcomes.
Expanding research across the brain’s fear circuitry
Halladay’s next step is to study astrocytes across the broader network involved in fear. The amygdala works in parallel with other brain regions. The prefrontal cortex helps us make decisions in frightening situations, and deeper regions in the midbrain, such as the periaqueductal gray matter, control responses such as cowering and fleeing.
The exact role of astrocytes in these regions is still unclear, but researchers believe it is likely that they also contribute.
“Understanding the larger circuitry may help answer a simple question: why people with anxiety disorders have inappropriate fear responses to things that are not actually dangerous,” Halladay said.
