Researchers from Tohoku University in Japan discovered that part of the memory selection process depends on a type of cell found in the nervous system called astrocytes. The study, the results of which were published in the journal “Glea” on November 4, showed that changing the pH around astrocytes did not affect short-term memory, but it contributed to forgetting these memories in the long term.
Which memories do I keep?
One of the brain’s most powerful assets is that it can store information as memories, allowing us to learn from our mistakes. However, some memories remain vivid, while others are forgotten.
Humans and animals take advantage of the recurring nature of events in their surroundings and store the relationships between apparent events in the form of memory. It is well known that memory formation is multistage, and it has generally been assumed that short- and long-term memory formation occurs sequentially. However, it is also possible that completely different cellular processes giving rise to short- and long-term memory begin simultaneously, but independently, at the moment of the same memorable experience.
Manipulation of astrocytes
The researchers used a technique called optogenetics to manipulate astrocytes, shining light on them through optical fibers inserted into the brains of mice. This enabled the researchers to directly stimulate astrocytes and either make them acidic or basal in that region. The researchers focused on the functions of astrocytes in the amygdala, an area of the brain known to be important in regulating emotions and fear.
The mice were given a mild electric shock in the experimental room, and when they were returned to the same room, the mice remembered the shock and froze in place as a natural response. In comparison, mice whose astrocytes were turned acidic immediately after a mild shock were able to temporarily retain the fear memory, but they forgot it by the next day. This shows that turning their astrocytes into eosinophils did not affect short-term memory, but it prevented long-term memory from being remembered.
Install memories
A different effect was observed in mice whose astrocytes were converted to basal cells. When tested 3 weeks later, the control mice that had not been manipulated showed signs of forgetfulness, manifested by decreased freezing upon entering the room. Mice whose astrocytes were converted to basal cells immediately after a strong shock still showed strong fear responses even after 3 weeks. This suggests that astrocytes play a key role in determining whether memories are erased or preserved for a long time, immediately after a traumatic event.
While memories are generally thought to be formed in a continuous process in which short-term memories are gradually preserved and become long-term memories, this research suggests that they may be preserved as both short-term and long-term memories at the same time.
“We think this could change the way we understand memory formation,” says Professor Ko Matsui of the Laboratory of Brain Physiology at Tohoku University, who led the research. He added: “The effect of astrocytes on memory is also likely to depend on different contexts, including mental, social or environmental factors.”
Study co-researcher Hiroki Yamao believes that astrocytes may hold the key to understanding emotional changes and memory formation. “This may be just a glimpse into how astrocytes influence the processing of emotional information,” Yamao explains.
Our next goal is to discover the mechanisms by which astrocytes regulate emotional memory. “Understanding these processes may pave the way for treatments that prevent the formation of traumatic memories, providing a valuable approach to treating disorders such as PTSD by interfering with memory formation.”