Ingrid Wickelgren writes:

The human brain is a vast network of billions of neurons. By exchanging signals to depress or excite each other, they generate patterns that ripple across the brain up to 1,000 times per second. For more than a century, that dizzyingly complex neuronal code was thought to be the sole arbiter of perception, thought, emotion, and behavior, as well as related health conditions. If you wanted to understand the brain, you turned to the study of neurons: neuroscience.

But a recent body of work from several labs, published as a trio of papers in Science in 2025, provides the strongest evidence yet that a narrow focus on neurons is woefully insufficient for understanding how the brain works. The experiments, in mice, zebra fish, and fruit flies, reveal that the large brain cells called astrocytes serve as supervisors. Once viewed as mere support cells for neurons, astrocytes are now thought to help tune brain circuits and thereby control overall brain state or mood — say, our level of alertness, anxiousness, or apathy.

Astrocytes, which outnumber neurons in many brain regions, have complex and varied shapes, and sometimes tendrils, that can envelop hundreds of thousands or millions of synapses, the junctions where neurons exchange molecular signals. This anatomical arrangement perfectly positions astrocytes to affect information flow, though whether or how they alter activity at synapses has long been controversial, in part because the mechanisms of potential interactions weren’t fully understood. In revealing how astrocytes temper synaptic conversations, the new studies make astrocytes’ influence impossible to ignore.

“We live in the age of connectomics, where everyone loves to say [that] if you understand the connections [between neurons], we can understand how the brain works. That’s not true,” said Marc Freeman, the director of the Vollum Institute, an independent neuroscience research center at Oregon Health and Science University, who led one of the new studies. “You can get dramatic changes in firing patterns of neurons with zero changes in [neuronal] connectivity.” [Continue reading…]