Every day you walk with your brain making a gentle rotation inside your skull. Like a soft yolk floating in a cloud of clear whites.
All it takes is a shock or sudden blow, and the brain is set aside with astonishing speed. Whether it hits the skull or turns, the damage can be severe, as we know from people who have experienced a traumatic brain injury.
But precisely what happens to the brain at that moment of impact? How does it move?
Research that investigates the biomechanics of brain injury usually includes crash-tested mannequins aimed at an accident, athletes wearing mouth guards, or helmets equipped with motion sensors, or models that simulate the human brain.
Now, scientists have thrown eggs into the mix.
How an egg yolk reacts when different forces are applied. (Lang et al., Physics of Fluids, 2021)
What began as a cooking curiosity for a team of engineers, with an egg scrambling instrument for home cooks, led them to study the fundamental physics that regulates the motion of soft matter in a liquid environment. , using an egg to mimic the brain.
“Critical thinking, along with simple experiments in the kitchen, led to a series of systematic studies to examine the mechanisms that cause egg yolk deformation,” said biomedical engineer Qianhong Wu of Villanova University of Pennsylvania.
While his approach was somewhat unusual, the results of this study help us understand how soft matter, like brain tissue, moves and deforms when exposed to external forces.
The more we know and explain the concussive forces that affect the brain, the better researchers can improve vehicle safety systems, design hats to protect them, and help athletes improve their technique to prevent injury.
Inside the skull, the brain rests on a shock-absorbing fluid called cerebrospinal fluid.
The most common and mild form of traumatic brain injury (TBI) is concussion, and the term actually comes from a Latin word meaning “shake violently.” But even a subconcussive blow to the head is enough to cause changes in the functioning of brain cells, according to studies.
As for the causes of brain injury, head rotation as a mechanism of brain injury was proposed in the 1940s. Easy to imagine if you think of a punch to the chin that throws your head back or if someone gets whipped from an attack.
But there is often confusion about the mechanics of concussion, as there are different ways to measure head impacts and use this information to predict brain injury.
Early research efforts examined linear or “linear” impacts, where the brain sinks in one direction and bounces off the skull. Then the focus became rotational forces that rotate the brain inside the skull.
Needless to say, it’s hard to gauge how the brain can actually twist with such an impact because we can’t look between people’s moving heads.
But scientists can still learn something by recreating the brain, coupled to its cerebrospinal fluid, using similar materials.
In this study, the researchers began by measuring the material characteristics of an egg yolk and its outer membrane, so that they could later quantify the stress in which the eggs were during laboratory experiments, which presented two configurations. .
“To damage or deform an egg yolk, one would try to shake and turn the egg as quickly as possible,” the study authors write in their paper, so that the eggs cracked in a transparent container and they were subjected to three types of impact.
The team observed how the egg yolks were compressed and stretched in different directions with an accelerated rotational impact, and also how they changed virtually nothing with a direct blow to the container.
When an egg-filled rotating container came to an abrupt stop, the yolk deformed “tremendously” with the decelerating rotational impact and it took about a minute to resume its original round shape.
“We suspect it’s rotational, mostly [decelerating] rotational, the impact is more detrimental to brain matter, ”Wu said.
The results of this study are parallel to previous research related to vehicle crash tests and pendulum head impacts, which found that rotational head impacts were a better indicator of the risk of traumatic brain injury than linear acceleration.
These results echo the general consensus that the brain is more sensitive to rotational motion than linear motion.
But that doesn’t mean we should completely discount straight-line impacts, as other researchers have proposed new injury metrics that combine linear and rotational head acceleration measures to assess the risk of concussion.
Brain injuries are complicated and, unfortunately, many are not detected. At least with this clever experiment, we can see the gross impact for ourselves.
The study was published in Fluid physics.