How does the brain store and access memories? Our understanding of the brain has (thankfully) come a long way since the days when we removed brain tissue to see what happens. But where our memories reside and how our brains recall past experiences remains elusive.
new paperpublished on November 6th natureexamines the role cells called astrocytes (named for their distinctive star-shaped shape) play in how mice process and store memories. This study suggests that these cells are involved in both memory formation and storage, challenging the established theory that memories are stored only in neurons.
Benjamin Deneen, lead author of the paper, says: popular science In the early days of neuroscience, research tended to focus on neurons and treat other cells as relatively unimportant supporting structures. However, as our understanding of the brain’s complexity has increased, we have also come to realize that, while important, neurons are not the only cells that contribute to brain function. In particular, the role of non-neuronal cells called glial cells, of which astrocytes are an example, has been thoroughly reconsidered.
“[Astrocytes] “For a long time, they were thought of as monolithic supporting cells in the brain,” Deneen says. However, he continued, “Our knowledge of astrocytes has experienced a renaissance over the past two decades, highlighted by the identification of their dynamic physiological activities, critical role in circuit function, and diverse molecular properties. ” he continues.
According to modern understanding, astrocytes appear to be responsible for a variety of functions in the brain. In fact, there are so many features that it can be difficult to simply answer the question of what Astrosite does. “Astrocytes, in my opinion, are like the ‘Swiss Army Knife’ of the brain,” Deneen says. “They interact with almost every cell in the brain. [and] One astrocyte can contact up to 100,000 synapses. ” He cites multiple examples of important activities in which astrocytes are involved.[They] Plays an important role in the formation of the blood-brain barrier. It provides metabolic support to neurons, buffers ions, and maintains ionic gradients. Response to injury and degeneration. [and] It interacts with resident immune cells in the brain in response to injury or other attacks. ”
Nevertheless, despite their importance, research on how astrocytes participate in memory formation and storage is still in its infancy.
The common understanding of how our brains store memories is that they are distributed throughout the brain in unique networks of neurons called “engrams.” Deneen explains: “At the cellular level… all memories are made up of ensembles, or engrams, of different neurons distributed throughout a host region of the brain. Importantly, a single neuron can participate in multiple engrams, but each An engram is made up of a unique collection of neurons.
The study looked at how astrocytes in the mouse brains, specifically a special type known as “learning-associated astrocytes,” or LAAs, act during and after learning. Researchers found that some of these LAAs become activated during such experiences. Reactivating the LAA in different environments appears to stimulate memory retrieval and associated learning.
The researchers also found that LAA activated by the learning experience maintained high levels of a protein expressed by a gene called NFIA. Blocking the production of this protein prevents the memory of the learning experience in question from being recalled.
Based on this evidence, astrocytes appear to play a role in both memory storage and recall. How does this square with the commonly accepted theory that memories are stored as engrams?
“This is a question we are currently struggling with in the lab,” Deneen laughs. “One way of thinking about this goes back to the fact that astrocytes ‘listen’ to neurons and respond to meet the demands of the circuits they function with. Under learning conditions, where ensembles of neurons form memory engrams, neurons may need to “offload” aspects of memory to astrocytes, which in turn may need to “offload” information stored by a particular engram Serves as a storeroom or storehouse. neuron. “
In any case, it is clear that there is still much to learn about the nuances of how memory works, and the apparent involvement of astrocytes raises many new questions and opens many new possibilities. It is also clear that this possibility is suggested. “It’s clear that astrocytes are involved in memory retrieval,” Deneen says. “Whether they actually store memory or act as a conduit for retrieval is unclear. Perhaps there is some ‘indexing’ between astrocytes and neurons at the cellular level; The neuron distributes its memory “information” to a host of nearby LAAs. ”
There are also many more questions to answer about the astrocytes themselves. For example, while the LAA is certainly a specialized cell, it is unclear whether there is a clearly predetermined type of astrocyte or a single cell that evolves to fulfill the required role. there is no. “I have been studying how astrocytes are created and how they function for more than 20 years,” Deneen says. white problem. There is evidence that different subtypes of astrocytes are encoded during development…but whether this “diversity” reflects a predetermined, hard-wired state or whether local Whether it is an adaptation to the environment is still a matter of debate. ”
