The brain is actually two organs
Neuroscience has long assumed that the human brain develops from a single progenitor cell, but a new study led by Stanford Medicine suggests otherwise. The team found that the brain is actually composed of two distinct organs — one governing automatic survival functions like breathing and heartbeat, and another responsible for higher-order thinking — that evolved separately and only later became physically joined.
By examining mouse embryos, the researchers identified two separate cell populations that never overlap. One becomes the forebrain and midbrain and the other is the hindbrain, and differences in how DNA is packaged in each cell cause different developmental fates.
Based on this insight, the team successfully grew functional human hindbrain motor neurons in a lab dish for the first time, which has been an obstacle for research into diseases like ALS and spinal muscular atrophy.
“Previous attempts to make hindbrain neurons likely tried to coax forebrain and midbrain progenitors into hindbrain cells, which our study shows is not possible,” said M.D. and Ph.D. student Rayyan Jokhai, a co-first author on the study.
The findings, published in Nature Neuroscience, will provide new possibilities for studying brain stem disorders that have been difficult to model in the lab.
Extreme heat
As heat waves grow longer and more frequent worldwide, Stanford researchers across engineering, medicine and earth sciences are testing practical ways to keep people and buildings cool.
In Makassar, Indonesia, where roughly 40% of residents live in informal settlements without air conditioning, a team led by Rishee Jain, associate professor of civil and environmental engineering, and John Openshaw, assistant professor of infectious diseases, is painting metal rooftops with reflective white paint, a low-cost intervention that can lower indoor temperatures by up to 5 degrees Fahrenheit. The team is also outfitting volunteers with wearable sensors to measure heart rate and sleep patterns, comparing results between painted and unpainted homes to build a case for wider adoption.
“Big interventions can take decades to bring into place, and we don’t have that time. People are suffering from events now,” Openshaw said.
Other researchers are tackling the problem from different angles. In San Francisco, Gregory Deierlein, John A. Blume Professor in the School of Engineering, is working with the city to model how buildings and residents would fare across combined hazards like heat waves and earthquakes, aiming to bundle solutions instead of addressing risks separately.
Catherine Gorlé, associate professor of civil and environmental engineering, is studying how natural ventilation and urban greenery can cool buildings and city blocks, pointing to Medellín, Colombia’s tree-planting campaign, which was linked to an average temperature drop of 2 degrees Celsius over three years.
“There is a lot of opportunity to bring green spaces and blue spaces back into cities, not only to make them in general nicer to live in, but also more comfortable during heat waves,” Gorlé said.
All of these research efforts reflect a push at Stanford to move quickly on practical and effective solutions as extreme heat becomes an unavoidable part of life in cities worldwide.
Tracking toxic metals in wildfire smoke
Stanford researchers are building systems to detect a danger in wildfire smoke that current air quality monitoring misses: toxic metals that are released when extreme heat transforms naturally occurring soil minerals into airborne particles.
The project, called SmokeCast, started with professor of earth system science Scott Fendorf’s investigation into the 2019 Kincade Fire, which showed that a fire’s location determines how much toxic metal ends up in its smoke.
This summer, the team tested a prototype device on a firetruck dispatched to a Colorado wildfire. The device is a briefcase-sized array of air filters and satellite sensors which provided the team with real-time data on temperature, humidity and gases like carbon monoxide, while also estimating the odds that nearby soils would release toxic metals.
Existing measures like the EPA’s Air Quality Index track fine particle concentration but not chemical composition. “It doesn’t tell you anything about chemistry, and that is a huge gap,” said Alexander Honeyman, postdoctoral scholar in Fendorf’s research group.
With backing from the Stanford Sustainability Accelerator, the team hopes to outfit more firetrucks with the sensors and eventually offer a public smoke-toxicity forecast in the coming years.