The human brain contains approximately 86 billion neurons, and scientists have assumed for decades that these cells are the primary drivers of memory and cognition. However, a new study by researchers at the Massachusetts Institute of Technology (MIT) suggests that another type of brain cell, long considered merely supportive tissue, may play a much larger role than previously thought.
The researchers suggest that astrocytes, star-shaped cells found throughout the brain, could help explain the brain’s remarkable memory capacity and overcome limitations in traditional theories of memory storage. The results were published in the journal Proceedings of the National Academy of Sciences.
Why MIT scientists are rethinking the brain’s support cells
Astrocytes are among the most abundant cells in the human brain, in numbers nearly identical to those found in neurons.
Despite their prevalence, they have traditionally been viewed as support cells responsible for maintaining the brain’s environment and assisting neurons rather than actively processing information.The MIT team says this view may be incomplete. Their research suggests that astrocytes could be directly involved in computation and memory storage, which may help the brain store much more information than neural models alone allow.
Lead author Leo Kozachkov worked alongside Jean-Jacques Slotin, a professor of mechanical engineering and brain and cognitive sciences at MIT, and Dmitry Krotov of the MIT-IBM Watson AI Lab to develop the new theory.Many modern theories of memory storage are based on models of neural networks known as Hopfield networks. These systems store memories as distributed patterns across connections between neurons.Although effective in explaining some aspects of memory, Hopfield networks face an important limitation: they can only store a limited number of patterns before memories begin to interfere with each other.Researchers later developed more advanced models called dense associative memories, which can store much larger amounts of information. However, these models require high-level interactions involving more than two neurons simultaneously, something that conventional synapses do not naturally provide.This has left scientists searching for a biological mechanism capable of supporting complex memory storage.
How astrocytes can solve the puzzle
Researchers at MIT believe astrocytes could provide this missing mechanism.Unlike neurons, astrocytes do not communicate through electrical impulses. Instead, they use calcium-dependent signals and can release chemical messages known as glial transporters.Each astrocyte extends thousands of delicate processes that can wrap around individual synapses, creating structures known as triple synapses.
These include three components: the presynaptic neuron, the postsynaptic neuron, and the astrocyte process.According to the new model, these tripartite connections may function as computational units rather than simple support structures. By participating in communication between neurons, astrocytes can establish the high-level interactions required for dense associative memory.
What the model suggests about memory capacity
One of the most interesting implications of the study concerns the limits of memory storage.Traditional neural network models eventually reach a limit where additional memories become difficult to store or accurately retrieve. The MIT model suggests that networks of astrocyte neurons may not face the same limitations.Instead, the amount of information that can be stored appears to grow with the size of the network itself. In theory, this means that memory capacity could become much larger than predicted by neuronal models alone.Researchers stress that this does not mean endless memory. Rather, it suggests that the brain may have a storage structure capable of supporting a much larger number of memories than previously thought.
Increasing evidence that astrocytes play an active role
Recent neuroscience research has increasingly indicated a more active role for astrocytes.Studies have shown that disrupting connections between astrocytes and neurons in the hippocampus can impair memory formation and retrieval.
Advances in calcium imaging technology have also allowed scientists to monitor the activity of astrocytes coordinating alongside neurons in real time.These findings do not prove the MIT hypothesis, but they support the broader idea that astrocytes are involved in information processing rather than simply maintaining neural infrastructure.As Slotin points out, there is no reason why evolution could not exploit the ability of astrocytes to connect to hundreds of thousands of synapses for computational purposes.Despite the excitement surrounding the study, the researchers stress that their work is currently a mathematical model rather than experimental evidence. The proposed mechanism has not yet been observed directly in living brains, and future experiments will be needed to determine whether astrocytes perform the type of memory-related computations suggested by the model.Krotov expressed hope that the study would encourage experimental neuroscientists to conduct further research into the hypothesis.
Such testing would be necessary before the theory could be accepted as an accurate description of how memory works in the brain.
What it could mean for neuroscience
If future experiments support this model, the implications could be significant. Neuroscientists may need to rethink one of the field’s basic assumptions: that the synapse between two neurons is the basic unit of memory storage.Instead, memory could depend on a more complex system that involves neurons and astrocytes working together. Such a discovery would not overturn existing knowledge about the brain, but it could expand it significantly.
