The folded structure of the human brain may be a physical-rather than biological-phenomenon, according to a study published online this week in Nature Physics. The research uses a 3D printing technique to confirm a controversial model that attributes this distinctive feature of brain development to mechanical compression.
The model, put forward in 1975, suggests that the brain’s shape can be explained as a physical growth process, in the absence of any biochemical factors. However, supporting evidence has proved difficult to obtain, due to ethical concerns associated with experiments on human brains and a lack of suitable alternatives.
Tuomas Tallinen, Lakshminarayanan Mahadevan and colleagues circumvented these challenges by 3D printing a model brain made from soft gels, based on a magnetic resonance image of a fetal human brain. Their brain comprised layers of different types of gel, designed to swell to different degrees when immersed in solvent, mimicking real brain growth. They show that the relative expansion of the layers created mechanical compression forces that in turn led to the formation of the familiar folds found in the human brain. The authors conclude that their experimental results, which they support with a numerical model, suggest that physical forces play a key role in neurodevelopment and may have implications for the diagnosis and treatment of a number of neurological disorders.
In an accompanying News & Views article, Ellen Kuhl writes: “the lack of experimental evidence has been the major point of criticism [of the model] from the neuroscience community…This work provides the essential missing link between modeling, experiment and simulation.”