For decades, astrocytes were thought to play a quiet supporting role in the brain. But new research suggests these star-shaped cells are deeply involved in how fear memories are formed, maintained, and extinguished.
Credit: Shutterstock
A new study reveals that astrocytes, once dismissed as mere support cells, play a central role in fear memory.
Imagine a star-shaped brain cell extending delicate branches that wrap around nearby neurons. This cell is called an astrocyte. For many years, scientists believed astrocytes mainly served as caretakers, helping hold neural networks together and supporting the connections that allow brain cells to communicate.
New research now challenges that long-standing view. A recent study reports that these widely distributed support cells play a role just as critical as neurons when it comes to forming and regulating fear memories.
“Astrocytes are interwoven among neurons in the brain, and it seemed unlikely they were there just for housekeeping. We wanted to understand what they’re actually doing – and how they’re shaping neural activity in the process,” said Lindsay Halladay, assistant professor at the University of Arizona Department of Neuroscience and one of the study’s senior authors.
Halladay’s laboratory partnered with researchers at the National Institutes of Health on the multi-institutional project, which was led by Andrew Holmes and Olena Bukalo of the Laboratory of Behavioral and Genomic Neuroscience.
The findings, published in Nature, focus on astrocytes located in the amygdala, a region often described as the brain’s fear center. The researchers found that these cells help the brain learn which experiences are threatening, assist in recalling those memories, and play an important role in extinguishing fear when it is no longer appropriate. The results challenge traditional ideas about how fear memories are stored and suggest new directions for treating conditions such as post-traumatic stress disorder.
“For the first time, we found that astrocytes encode and maintain neural fear signaling,” Halladay said.
Watching Fear Form in Real Time
To explore how fear learning unfolds, the team used a mouse model to study how fear memories form, how they are retrieved, and how neurons and astrocytes each contribute to the process.
With the help of fluorescent activity sensors, the researchers tracked astrocyte responses in real time during the creation and recall of fear memories. Astrocyte activity rose as memories were formed and retrieved, then declined as those memories were extinguished.
The scientists then adjusted the signals astrocytes send to nearby neurons. When they boosted or reduced those signals, the strength of fear memories changed in step. This showed that astrocytes are not merely supporting actors but directly influence how fear is encoded and expressed.
Altering astrocyte function also reshaped broader neural activity. When astrocyte signaling was disrupted, neurons were unable to generate typical fear-related patterns of activity. As a result, they struggled to pass along information about appropriate defensive responses to other brain regions that coordinate behavior. These results push back against neuron-centered models of fear by demonstrating that neurons alone do not account for how fear memories are produced.
The effects were not limited to the amygdala. Interfering with astrocytes also changed how fear-related signals traveled to the prefrontal cortex, a region essential for decision making. This indicates that astrocytes influence not only how fear memories are encoded in the amygdala, but also how those memories guide responses in complex situations.
Implications for Anxiety and PTSD
Halladay said that recognizing the role of astrocytes in retrieving fear memories could reshape treatments for disorders marked by persistent fear, including post-traumatic stress disorder, anxiety disorders, and phobias. If astrocytes help control whether fear memories are expressed or successfully extinguished, then therapies aimed at astrocyte-related pathways may one day complement approaches that focus primarily on neurons.
Her next step is to investigate astrocyte activity throughout the broader fear network in the brain. The amygdala works in coordination with other regions. The prefrontal cortex contributes to decision-making during threatening situations, while deeper structures such as the periaqueductal gray in the midbrain, carry out defensive actions like freezing or fleeing. Although the precise role of astrocytes in these areas remains uncertain, Halladay believes there is a strong possibility that they also shape neural function there.
“Understanding that larger circuit could help answer a simple question of why someone with an anxiety disorder might exhibit inappropriate fear responses to something that isn’t actually dangerous,” Halladay said.
To explore how fear learning unfolds, the team used a mouse model to study how fear memories form, how they are retrieved, and how neurons and astrocytes each contribute to the process.
With the help of fluorescent activity sensors, the researchers tracked astrocyte responses in real time during the creation and recall of fear memories. Astrocyte activity rose as memories were formed and retrieved, then declined as those memories were extinguished.
The scientists then adjusted the signals astrocytes send to nearby neurons. When they boosted or reduced those signals, the strength of fear memories changed in step. This showed that astrocytes are not merely supporting actors but directly influence how fear is encoded and expressed.
Altering astrocyte function also reshaped broader neural activity. When astrocyte signaling was disrupted, neurons were unable to generate typical fear-related patterns of activity. As a result, they struggled to pass along information about appropriate defensive responses to other brain regions that coordinate behavior. These results push back against neuron-centered models of fear by demonstrating that neurons alone do not account for how fear memories are produced.
The effects were not limited to the amygdala. Interfering with astrocytes also changed how fear-related signals traveled to the prefrontal cortex, a region essential for decision making. This indicates that astrocytes influence not only how fear memories are encoded in the amygdala, but also how those memories guide responses in complex situations.
Implications for Anxiety and PTSD
Halladay said that recognizing the role of astrocytes in retrieving fear memories could reshape treatments for disorders marked by persistent fear, including post-traumatic stress disorder, anxiety disorders, and phobias. If astrocytes help control whether fear memories are expressed or successfully extinguished, then therapies aimed at astrocyte-related pathways may one day complement approaches that focus primarily on neurons.
Her next step is to investigate astrocyte activity throughout the broader fear network in the brain. The amygdala works in coordination with other regions. The prefrontal cortex contributes to decision-making during threatening situations, while deeper structures such as the periaqueductal gray in the midbrain, carry out defensive actions like freezing or fleeing. Although the precise role of astrocytes in these areas remains uncertain, Halladay believes there is a strong possibility that they also shape neural function there.
“Understanding that larger circuit could help answer a simple question of why someone with an anxiety disorder might exhibit inappropriate fear responses to something that isn’t actually dangerous,” Halladay said.
The Life of Earth
https://chuckincardinal.blogspot.com/
Fear is a built in factor of ones brain, connecting our actions and memories. Learning to deal with ones fear shapes who you are. Leaving it to the unconscious mind steals ones freedom and self determination. Fear can make you super human.
ReplyDelete