Scientists think they've learned how the human brain is able to store so much information

Astrocytes are the brain’s star-shaped support cells, and they might be doing more than just backing up neurons.

While we usually credit neurons for storing memories and processing thoughts, astrocytes are just as abundant and far more involved than was once believed.

The human brain contains about 86 billion neurons, each firing electrical signals that help us think, feel, and remember. But alongside them, astrocytes quietly handle cleanup, deliver nutrients, and manage blood flow.

For a long time, these cells were seen as background players. Now, scientists are starting to see them in a new light.

A recent study from the Massachusetts Institute of Technology (MIT) suggests astrocytes could play a central role in how the brain stores memories, potentially changing how we understand this process.

Astrocytes have unique signals

Unlike neurons, astrocytes don’t generate electrical impulses. Instead, they use calcium signals to communicate.

These signals travel through thin extensions, called processes, that can wrap around the junctions where neurons connect – known as synapses. This forms what’s called a “tripartite synapse” involving a presynaptic neuron, a postsynaptic neuron, and the astrocyte process.

For years, the exact role astrocytes played in memory remained a mystery. But new imaging technology has revealed that calcium signaling allows astrocytes to sync their activity with neurons.

This means they don’t just observe what’s happening – they’re actively participating by releasing chemical messengers called gliotransmitters, which affect synaptic function.

“There’s a closed circle between neuron signaling and astrocyte-to-neuron signaling,” said Leo Kozachkov, the paper’s lead author.

“The thing that is unknown is precisely what kind of computations the astrocytes can do with the information that they’re sensing from neurons.”

New kind of memory model

Inspired by this feedback loop, MIT researchers built a model to test what astrocytes might be doing with the information they receive. They based their approach on a type of artificial neural network called a Hopfield network.

While useful in theory, Hopfield networks don’t have enough storage capacity to explain how the brain actually works. A newer version called dense associative memory boosts this capacity by linking more than two neurons at a time.

But there’s a catch – in real life, synapses usually only connect two neurons. That’s where astrocytes come in.

“If you have a network of neurons, which couple in pairs, there’s only a very small amount of information that you can encode in those networks,” explained Dmitry Krotov, a research staff member at the MIT-IBM Watson AI Lab and IBM Research.

Coupling neurons with astrocytes

According to Krotov, in order to build dense associative memories, you need to couple more than two neurons.

Because a single astrocyte can connect to many neurons, and many synapses, it is tempting to hypothesize that there might exist an information transfer between synapses mediated by this biological cell.

“That was the biggest inspiration for us to look into astrocytes and led us to start thinking about how to build dense associative memories in biology,” Krotov continued.

The result? A hybrid model that treats astrocytes as computing units in their own right.

Each process of an astrocyte is considered a unit capable of interacting with many synapses. Together, they help form a system that can store far more information than traditional neuron-only models.

Small cells, big storage

One unique feature of this model is how it views astrocytes. Instead of seeing them as a single cell, it breaks them down into many processes – each one acting like its own little calculator.

This division helps explain how the brain might pack in so much memory with relatively low energy use.

“By careful coordination of these two things – the spatial temporal pattern of calcium in the cell and then the signaling back to the neurons – you can get exactly the dynamics you need for this massively increased memory capacity,” Kozachkov explained.

Astrocytes reach far and wide

Supporting this theory is the physical layout of astrocytes. Each one touches hundreds of thousands of synapses.

The researchers believe that patterns in calcium flow within astrocytes could encode memories. These patterns could then influence neurons by releasing gliotransmitters at key synapses.

“By conceptualizing tripartite synaptic domains – where astrocytes interact dynamically with pre- and postsynaptic neurons – as the brain’s fundamental computational units, the authors argue that each unit can store as many memory patterns as there are neurons in the network,” said Professor Maurizio De Pitta from the Krembil Research Institute, University of Toronto, who was not involved in the study.

“This leads to the striking implication that, in principle, a neuron-astrocyte network could store an arbitrarily large number of patterns, limited only by its size,” he added.

So, are astrocytes the key?

To find out if this model reflects reality, researchers hope to test it by manipulating the connections between astrocyte processes and observing the impact on memory.

“We hope that one of the consequences of this work could be that experimentalists would consider this idea seriously and perform some experiments testing this hypothesis,” Krotov said.

This theory also holds promise beyond neuroscience. It could change how artificial intelligence systems are designed. By mimicking how astrocytes link various neurons together, future AI models might unlock more efficient memory storage.

“While neuroscience initially inspired key ideas in AI, the last 50 years of neuroscience research have had little influence on the field, and many modern AI algorithms have drifted away from neural analogies,” remarked Slotine.

“In this sense, this work may be one of the first contributions to AI informed by recent neuroscience research.”

The quiet stars of the brain may hold more memory power than anyone imagined. With a better understanding of astrocytes, both brain science and artificial intelligence could be in for a rethink.

The full study was published in the journal Proceedings of the National Academy of Sciences.

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