The human brain breaks apart 10 times as easily as polystyrene foam

Researchers used MRI scans and an algorithm to measure the stiffness and resilience to pressure of the brain in living people

By Karmela Padavic-Callaghan

Though they may look like they’re made from rubber, human brains are softer and squishier. Their ability to resist pressure is like that of a slab of gelatine, and they break apart more easily than polystyrene foam used for packaging.

Nicholas Bennion at Cardiff University in the UK and his colleagues set out to develop a method for obtaining more accurate measurements of the brain’s physical properties inside living humans. Most of what we know about how brain tissue reacts to instruments touching it during neurosurgery comes from organs that have been cut into or removed and preserved in chemicals, which can affect tissue stiffness and resiliency.

Combining a machine learning algorithm with MRI scans of people lying face down and then face up to shift the location of the brain in the skull, the researchers were able to work out different material characteristics of the brain and tissues that connect it to the skull. They quantified how much the brain collapses when pressed on, how it reacts to being pushed sideways and how springy the connective tissues are.

“If you take a brain which hasn’t been preserved in any way, its stiffness is incredibly low, and it breaks apart very easily. And it really is probably a lot softer than most people realise,” says Bennion.

The team found that brain matter collapses up to 10 times more easily than polystyrene foam and that its resilience to being pushed sideways is about a thousandth of what it would be if it were made from rubber – meaning its squishiness is comparable to a slab of gelatine. Bennion says that the algorithm calculated that the tissues connecting the brain to the skull were also fairly soft, possibly to protect the brain from moving too abruptly.

Though researchers have long known that brains are very soft and very fragile, the new study makes that notion precise enough to better inform sensitive surgical procedures, says Ellen Kuhl at Stanford University in California.

The new method, however, may not fully capture the way the brain deforms during motions more violent than shifting positions, such as head trauma in an impact sport or traffic accident, says Krystyn Van Vliet at the Massachusetts Institute of Technology. In these situations, the flow of fluids within the brain can change its material properties.

The team hopes their model can now be used to predict brain shifts that will occur doing surgery for each individual patient based on pre-operative MRI scans. This may eliminate the need for inserting and re-inserting instruments into the brain until they hit the correct spot, making procedures less invasive.

Reference: Journal of the Royal Society Interface, DOI: 10.1098/rsif.2022.0557