Scientists 3D print the human brain to reveal the mystery of fold formation

According to the Los Angeles Times, scientists at Harvard University in the United States have discovered how the human cerebral cortex produces folds by 3D printing a gel brain and observing its 'growth process'. They point out that changes in the number, size, shape, and location of nerve cells during human brain development can cause the gray matter to expand, causing the cortex to become 'mechanically unstable' under stress, eventually forming folds. The latest findings, published in a recent issue of the journal Nature Physics, will reveal a mystery about the structure of the human brain's gray matter that has puzzled scientists for years, and could help treat certain diseases associated with insufficient or excessive folds in the cerebral cortex. Ellen Kuhl of Stanford University in the United States said they provided the first experimental evidence for the differential growth theory, demonstrating that physical forces are not just biochemical processes, which are crucial in neurodevelopment. . This finding is important for clinical diagnosis and treatment, and helps prevent a variety of neurological diseases. When you think of the brain, pink, wrinkled objects appear like a deflated basketball, but not all species have wrinkled brains. For example, the smaller mouse brain is a smooth pink structure. Human babies don't form folds until 23 weeks of gestation. The researchers immersed the 3D model of the brain in a liquid solvent, which caused the outer layer, similar to the elastic cortex, to grow, eventually forming a folded structure similar to the real brain. Scientists have long known that brain folds have many benefits — cortical folds have more connectivity than smooth surfaces, says Kuhl: 'Each cortical neuron makes connections with 7,000 other neurons, resulting in a long 150,000 kilometers of nerve fibers.' Many researchers have tried to discern how these cells or biochemical processes work, but Harvard physicist Lakshminarayanan Mahadevan decided to study the folds of the brain. physical principles, and designed a mathematical model of the brain. It is reported that more than 40 years ago, another Harvard research team believed that growth differences in brain tissue could explain the fold structure. Researchers plan to reveal the growth characteristics of brain folds, but it is very difficult to directly use the human brain in experiments. At present, Harvard University has set up a research team to use 3D printing technology to reveal how the human cerebral cortex grows and produces folds. First, they used magnetic resonance images of the smooth fetal brain of a 22-week-old fetus to 3D print a gel model that mimics the brain's 'white matterorganize)'. The researchers then immersed the 3D model of the brain in a liquid solvent, which caused the elastic cortex-like outer layer to begin to grow, eventually forming a folded structure similar to the real brain. The results showed that the cortical tissue began to grow, but it was only anchored to the white matter, and with the cortical expansion, eventually the structure collapsed, forming the gyri and deep grooves that covered the surface of the cerebral cortex. 'We found that the growth of brain folds is closely related to changes at the molecular level, biochemical processes that cause cells to move, divide and change shape, and change in number,' Mahadevan said. This means that changes in the number, size, shape, and location of nerve cells cause gray matter to expand, mechanically destabilizing the cerebral cortex under pressure from physical forces, and eventually forming a wrinkled structure. This research will help scientists better understand various neurological diseases, and will also help us identify topographical markers for early diagnosis of autism, schizophrenia or Alzheimer's disease, and ultimately design more efficient treatments.