Researchers have grown a 3D replica of a brain in a laboratory and successfully reproduced its wrinkled, folded shape. The new study published in Nature Physics may have finally answered the long-standing question of how the folds in our brains form, with the process seemingly determined more by the laws of physics than the driving forces of biology.
The reason our brains have a creased structure is clear from an evolutionary perspective: Folded brains shorten the distance that different sections have to communicate over. In addition, folding allows more of the cortex, the brain's outer layer, to fit into a human skull. As we grow into adults, the brain’s volume increases 20 times, but the surface area – thanks to these folds – increases 30 times.
Without these folds, our cognitive capabilities would be dramatically limited. While we therefore know our brain’s organic origami has a distinct “purpose,” how these folds arise in the first place has been far less clear. But a team of Harvard University researchers suspected that there might actually be a fairly simple, non-biological mechanism behind the development of the folds, grooves (sulci) and ridges (gyri) – a process known as gyrification.
In order to test this theory, a 3D printed, gel-based replica of a brain was produced, based on magnetic resonance imaging (MRI) scans of an actual fetal brain. Still smooth and unfolded, this model was coated in a one-millimeter-thick (0.04-inch) second layer of elastomer gel, a material analog for the cortex, and placed into a particular solvent.
The "cortex" development of the replica fetal brain. The study's results are a no-brainer, really. Mahadevan Lab/Harvard SEAS
Within just a few minutes of being immersed, the elastomer gel rapidly absorbed the solvent, making it grow out from the underlying gel. In order for it to stay attached to the underlying gel, the expanding gel began to mechanically contract and buckle, folding in on itself. The final result looked remarkably similar to the sulci pattern observed on a real fetal brain.
Previous theories on the driving processes behind gyrification have been more biology-focused, with one prominent idea being that the folds are induced by biochemical signals from within the brain, which subsequently causes the expansion and contraction of the cortex. This would allow certain, high priority regions of the brain to be better connected than others.
However, this study implies that physical, rather than biological, processes largely determine our brain’s folding pattern. Understanding the early stages of brain development is critical if researchers are to uncover the genesis of a range of neurodevelopmental brain disorders, including anencephaly, wherein a fetus’ early brain foundations begin to improperly form.
“Brains are not exactly the same from one human to another, but we should all have the same major folds in order to be healthy,” said Jun Young Chung, a postdoctoral fellow at Harvard University and coauthor of the study, to the Harvard Gazette. “Our research shows that if a part of the brain does not grow properly, or if the global geometry is disrupted, we may not have the major folds in the right place, which may cause dysfunction in the brain.”