Serotonin Wiring, a Tipping Crust, Iron Haze

Serotonin neurons in the mouse brain fall into five distinct groups, and each group sends its fibers to a set of functionally related brain regions. That is the main finding of a study published last month in Cell. It is the first projectome, or whole-brain map of connections, for the serotonin system of any vertebrate. Another team mapped the full serotonin system of a roundworm in 2023.

How the map was made

The team, which includes Stanford neurobiologist Liqun Luo, built on mouse work from 2018. They used viral-genetic tracing to follow serotonin neurons that start in the dorsal and median raphe, two clusters in the brainstem. Mice were injected with a virus that makes connected serotonin neurons light up across the whole brain. The researchers then imaged the brains and repeated the process until they had covered every area that serotonin reaches.

The five projection groups are:

• the hippocampal-entorhinal network
• the basal ganglia
• the cortex
• the medial interbrain (medial thalamus and hypothalamus)
• the brainstem and lateral thalamic nuclei

The authors argue that the system is organized by what its target regions do, not by how close they are. There are exceptions. The central and basolateral amygdala sit next to each other and both help regulate fear and emotion, yet they belong to different groups. That split matches their different developmental origins and cell types.

Genes, location and behavior

Earth's solid outer layers, the mantle and crust, can tilt as a single unit over the liquid core. Geologists call this true polar wander because the planet's actual poles move, not its magnetic ones. It happens because mantle flow and crustal changes make some regions denser than others, which throws off the planet's balance. The solid Earth then rotates to redistribute that mass.

The process is happening now. Satellite measurements show the poles moving about 10 centimeters a year, mostly because ice caps are melting, says Mathew Domeier, a University of Oslo geoscientist and lead author of a new study in Science. The open question was whether true polar wander runs slowly and steadily or comes in short, fast bursts. The main evidence so far, magnetic signals locked in ancient rocks, is sparse and doesn't settle it.

Reading the clover in old floods

Domeier's team tried a different kind of evidence. Earth's spin makes both rock and ocean bulge at the equator. When the solid Earth tips, it gets dragged through the ocean's bulge while the water stays in place. Some land rises out of the sea and other land goes under. From the rock record this looks like sea-level change, but Domeier says it isn't: the continents moved, not the water. The result has a recognizable shape. Two opposite quarters of the globe flood and the other two dry out, making a four-leaf-clover pattern.

The researchers searched maps of submerged and exposed continents, built at 10-million-year intervals, for that pattern. It shows up around 200, 150 and 100 million years ago, and again between 30 and 20 million years ago. That makes at least four episodes in the past 320 million years. Domeier says the result "took me quite by surprise."

Physicists at the National University of Singapore have built what they report is the most accurate atomic clock yet. It uses atoms of lutetium-176 and is accurate to 19 decimal places, a 41% improvement over the previous record holder. The work was published in Nature on Sept. 23.

Why the second needs a new definition

Since 1968, the International Bureau of Weights and Measures (BIPM) has defined the second by counting oscillations of the radiation from cesium-133 atoms, about 9.19 billion per second. Before that, the second was a fraction of the length of the year 1900. Later clocks built on other elements, including ytterbium and strontium, now outperform cesium. The BIPM is expected to redefine the second around 2030 using this newer generation, so the competing clock designs are effectively in a selection race.

Every atomic clock runs into the same problem: tiny changes in temperature, magnetic fields and gravity shift the atom's ticking frequency. Many designs need their surroundings held steady to within a few thousandths of a degree.

How the lutetium clock gets around it

The team says lutetium-176 is naturally insensitive to these disturbances, especially magnetic fields and temperature. It keeps time accurately even when the surrounding temperature swings by 5 degrees. Co-author Murray Barrett compares timekeeping to an ultramarathon and calls lutetium "a natural born endurance athlete."

On top of that, Barrett's lab developed a method called hyperfine averaging, which the researchers say cancels out the most important remaining environmental effects. The article doesn't explain how it works. Hyperfine levels are closely spaced energy states within the atom, and the name suggests the clock combines measurements from several of them so that their individual shifts average out. That is an inference from the name, not something the article states.

Hannah Ritchie writes that she expected climate change to make malaria worse. The research tells a messier story. Warming is shifting where the disease spreads across Africa, and by some estimates it could slightly lower the total burden.

Some background helps. Malaria causes about 280 million cases and 600,000 deaths a year. More than 95% of the deaths are in sub-Saharan Africa, roughly half of all deaths are in West Africa, and about 70% are children.

Transmission peaks at one temperature

In Africa, the mosquito Anopheles gambiae carries the parasite Plasmodium falciparum, and its transmission depends heavily on temperature. Spread peaks at about 25°C and drops to nearly zero below 16°C or above 34°C. Rain and humidity also matter. Moderate rain leaves standing water where larvae grow, but heavy rain washes them away.

A 2026 Nature paper by compared Africa as it warmed from 1901 to 2014 with a modelled Africa that had no human-driven warming. Warming added about , a small amount when about 240 in 1,000 carry the parasite. The result is uncertain: 59% of the simulations showed an increase, and the range ran from 4 fewer to 6 more cases per 1,000.

Venus's atmosphere contains a haze with an unidentified absorber that has puzzled scientists for decades. A team led by Karyu, publishing in Nature Astronomy, now points to a source from outside the planet: cosmic dust, and specifically the iron it brings in.

Note: the article text provided starts partway through, so some background and details of the team's methods are missing here.

Why iron

Meteorites typically carry magnesium, silicon and iron. Magnesium and silicon absorb ultraviolet light poorly, so they were never good candidates. Iron was more promising, and there was already evidence that it was present. The Soviet Venera and Vega probes detected iron in the atmosphere, and the mass spectrometer on NASA's Pioneer Venus Large Probe found iron sulfate. For decades, nobody could explain these detections.

Researchers had long suspected that iron compounds were the absorber. The new work supports that idea by showing that iron sulfate's properties match those of the haze.

How the particles move

The study also describes how these dust-derived particles behave in the clouds. Between about 40 and 50 km (25 to 31 miles) above the surface, sulfuric acid cannot condense onto the haze particles. Their high energy creates a nucleation barrier that stops sulfuric acid droplets from sticking to their surfaces. Instead of growing into cloud droplets there, the particles are carried upward by convection in rising hot air. In the upper cloud layer they cool enough to be taken up into sulfuric acid particles. Earlier observations had hinted at this process. According to the article, Karyu's team now has stronger evidence for it.