Quanta Magazine

Encased in the skull, perched atop the spine, the brain has a carefully managed existence. It receives only certain nutrients, filtered through the blood-brain barrier; an elaborate system of protective membranes surrounds it. But that privileged space also contains a mystery. For more than a century, scientists have wondered: If it’s so hard for anything to get into the brain, how does the brain’s waste get out? The brain has one of the highest metabolisms of any organ in the body, and that process must yield by-products that need to be removed. In the rest of the body, blood vessels are shadowed by a system of lymphatic vessels. Molecules that have served their purpose in the blood move into these fluid-filled tubes and are swept away to the lymph nodes for processing. But blood vessels in the brain have no such outlet. Several hundred kilometers of them, all told, seem to thread their way through this dense, busily working tissue without a matching waste system. However, the brain’s blood vessels are surrounded by an open, fluid-filled space. In recent decades, the cerebrospinal fluid, or CSF, in those spaces has drawn a great deal of interest. “Maybe the CSF can be a highway, in a way, for the flow or exchange of different things within the brain,” said Steven Proulx, who studies the CSF system at the University of Bern.? A recent paper in Cell contains a new report about what is going on around the brain and in its hidden cavities. A team at the University of Rochester led by the neurologist Maiken Nedergaard asked whether the slow pumping of blood vessels throughout the brain might be able to push the fluid around, among, and in some cases through cells, to potentially drive a system of drainage. In a mouse model, researchers injected a glowing dye into the fluid, manipulated the blood vessel walls to trigger the pumping action, and saw the dye concentration increase in the brain soon after. They concluded that the movement of blood vessels might be enough to move CSF, and possibly the brain’s waste, over long distances. The team took a further step in their interpretation. Because this kind of pumping — distinct from the familiar pulse from the heart — is regularly observed during sleep, they suggest that perhaps their observations can help explain why sleep feels refreshing. But it’s a hypothesis that?not everyone agrees is well founded. When it comes to ascribing purpose to the fluid moving through the brain, many researchers believe that the truth is still elusive. ?? Keep reading: https://lnkd.in/e9ZcnneV ?? Chanelle Nibbelink for Quanta Magazine

Beginning in the 1970s, sleep psychologist Irene Tobler set out behavioral criteria to show that sleep is not unique to higher-order mammals — even cockroaches sleep. (From the archive) https://lnkd.in/eerRXUb

Happy allergy season! Have you ever wondered why some over-the-counter allergy medicine can make you sleepy? “First generation” antihistamines like Benadryl could sneak past the barrier between the brain and the bloodstream. https://lnkd.in/eMu24Q-2

Metabolism helps drive cell differentiation. Take the humble slime mold: Under starvation conditions, the mitochondria in each Dictyostelium cell generate a burst of reactive oxygen species — small, unstable molecules that can damage proteins and DNA, and can also act as signaling molecules. As a result, individual cells aggregate and form a sort of multicellular slug, which crawls as a single unit and forms fruiting bodies to reproduce. https://lnkd.in/e2Gds93S

Read the explainer: https://lnkd.in/e9ZcnneV

In the history of evolution, multicellularity has evolved independently at least 50 times. But we’ve only figured that out in the past few decades. Listen to the first episode of the new season of “The Joy of Why” with co-hosts Steven Strogatz and Janna Levin. https://lnkd.in/etCGxSTB

Some variants of Dijkstra’s algorithm have seen real-world use in software like Google Maps. https://lnkd.in/e5h6aAhg

This is a microscopic view of apoptosis, the process by which cells violently self-terminate. Some evolutionary biologists suspect that this mechanism originated in the bacterial ancestors of mitochondria. (From the archive) https://lnkd.in/gcDg8XC2

Masaki Kashiwara has won the 2025 Abel Prize “for his fundamental contributions to algebraic analysis and representation theory.” https://abelprize.no In his early 20s, he established the theory of D-modules, a powerful framework for understanding systems of partial differential equations using methods from algebra and geometry. This work was foundational in establishing the burgeoning field of algebraic analysis. But it also had a surprising influence in representation theory, a branch of math that makes it easier to study important but abstract collections of symmetries. Kashiwara continued to shape these fields throughout his career. Read more about algebraic analysis: https://lnkd.in/e3cJjtgN Read more about representation theory: https://lnkd.in/d8v_ckY

The Dark Energy Spectroscopic Instrument, mounted on a telescope atop Kitt Peak in Arizona, is equipped with thousands of swiveling robotic eyes. Since May 2021, these eyes have flitted back and forth night after night, pointing their fiber optic cables at galaxy after galaxy and collecting their light. DESI’s first year of data covered six million galaxies; the new three-year data set spans nearly 15 million. https://lnkd.in/eVDp_CVD