Harvard researchers have used 3D printing to create a replica of the human brain.
Despite being arguably the most important organ in the human body, scientists still understand very little about the brain’s structure and how it works. Hypotheses abound, but there have been few opportunities to explore them until now.
The Harvard researchers 3D-printed a gel brain to watch it grow, helping them make new inferences about how it develops its signature folds.
The study could help solve the mystery behind the structure of gray matter and help explain psychological disorders caused by under or overfolding of the brain.
Not all brains found in nature have the same distinctive folds as the human brain does. Many smaller species, such as rats, have completely smooth brains.
In a commentary about the study, Ellen Kuhl of Stanford University said the researchers "demonstrated that physical forces — not just biochemical processes alone — play a critical role in neurodevelopment. Their findings could have far-reaching clinical consequences for diagnosing, treating and preventing a wide variety of neurological disorders.”
Humans don’t start developing the folds in the womb until roughly 23 weeks of gestation. The folds also continue to develop after they’re born. We do know that there are some benefits to having a folded structure. For example, the folds allow for greater connectivity across the gray matter (surface layer of the brain).
Kuhn said, “Each cortical neuron is connected to 7,000 other neurons, resulting in 0.15 quadrillion connections and more than 150,000 km of nerve fibres.”
It’s believed that the unique nature of human brain gyrification, the scientific term for the brain’s growth, is that it’s a response to the need to maximize the amount of cortical neurons in a small space. The Harvard researchers put this to the test with their 3D printed growing brain, and concluded that the folds are the result of physical growth processes instead of biological need.
The 3D printed model received no chemical directives to develop folds (like the hypothesis predicts)— instead, it developed folds naturally in response to mechanical compression forces during growth.
The benefit for the placement of the cortical neurons is only a response to the process of growth, not an evolutionary mechanism in and of itself.
The researchers ran their simulation by creating a 3D printed model based on MRI data, with several layers of soft gel material. The layers were designed to expand when placed in a solvent, simulating the growth of the brain’s gyro and sulci (folds). The results were published recently in Nature Physics.
The experiment is a first step in opening new lines of research that can benefit doctors and neuroscientists in their efforts to understand the brain and its disorders. And while the 3D-printed gel brain is a far cry from a true physical model, it can still tell us a lot. Understanding the intricacies of brain growth may help scientists identify physical marketers linked to certain diseases, such as autism, schizophrenia or Alzheimers.