Japanese scientists just built human brain circuits in the lab
Researchers in Japan built a miniature human brain circuit using fused stem-cell–derived organoids, allowing them to watch the thalamus and cortex interact in real time. They found that the thalamus plays a decisive role in maturing the cortex and organizing its neural networks. Signals from the thalamus triggered synchronized activity in specific neuron types, while others remained unaffected. The system closely mimics human brain development and could transform how scientists study neurological disorders.
A research team in Japan has successfully recreated key human neural circuits in the laboratory using tiny, multi region brain models called assembloids. These structures are grown from induced pluripotent stem (iPS) cells and are designed to mimic how different parts of the human brain connect and communicate. Using this system, the scientists showed that the thalamus plays a central role in shaping specialized neural circuits within the human cerebral cortex.
The study was published in the journal Proceedings of the National Academy of Sciences of the United States of America.
Why Cortical Neural Circuits Matter
The cerebral cortex contains many different types of neurons that must communicate effectively with one another and with other brain regions. These connections are essential for core brain functions, including perception, thinking, and cognition.
In people with neurodevelopmental conditions such as autism spectrum disorder (ASD), these cortical circuits often develop or function abnormally. Because of this, understanding how neural circuits form and mature is critical for uncovering the biological roots of these disorders and for developing new treatments.
The Thalamus and Its Role in Brain Wiring
Earlier research in rodents has shown that the thalamus plays an important role in organizing neural circuits in the cortex. However, how the thalamus and cortex interact during circuit formation in the human brain has remained largely unknown.
Studying this process directly in humans is difficult due to ethical and technical limitations on obtaining brain tissue. To overcome these challenges, scientists have turned to organoids, which are three dimensional structures grown from stem cells that resemble real organs.
From Organoids to Assembloids
While organoids are useful, a single organoid cannot capture the complex interactions between different brain regions. To study neural circuit formation more realistically, researchers use assembloids, which are created by physically combining two or more organoids.
Professor Fumitaka Osakada, graduate student Masatoshi Nishimura, and their colleagues at the Graduate School of Pharmaceutical Sciences at Nagoya University developed assembloids that model interactions between the thalamus and the cortex.
The team first generated separate cortical and thalamic organoids from human iPS cells. These organoids were then fused together, allowing the researchers to observe how the two brain regions interact as they develop.
Mini Brain Circuits That Behave Like the Real Thing
The researchers observed that nerve fibers from the thalamus grew toward the cortex, while cortical fibers extended toward the thalamus. These fibers formed synapses with one another, closely resembling the connections seen in the human brain.