The final piece of the computational puzzle was incorporating the orientation of the axons into the models. In this regard, modern brain imaging tools proved critical.

Diffusion tensor imaging, a form of MRI, is able to measure the direction of the flow of water through tracts in the white matter of the brain. Though it doesn’t help to illuminate damage necessarily, it can tell the researchers important information about the alignment of the fibers of the brain.

“It can tell us where the wires go,” says Ramesh. Like the grain in wood, the alignment of the axons—the wires in Ramesh’s analogy— makes the tissue stronger in some directions and weaker in others.

Combining all three factors in his calculations—anisotropy, rotational acceleration, and axonal orientation—Ramesh paints a remarkably detailed picture of traumatic brain injury in his model and has revealed some surprising findings about brain trauma.

The first is that the human brain is actually quite good at sustaining head-on motions and, to a lesser degree, side-on, lateral movements. This is likely due to the fact that humans have evolved as bilaterally symmetric organisms, and the majority of axons have naturally followed suit, aligning to better endure forces in certain directions.

Just as the model shows where the brain is most resilient, however, it also demonstrates where it is most vulnerable. Ramesh and team have found that the greatest damage to axons occurs from rotational motion, as if the brain were being wrung like a washcloth. In mechanical science, this stress is known as shear.

Boxing fans might imagine the classic knockout punch to the jaw that can drop a heavyweight in an instant. It is believed that this shearing motion stretches the axons to the point that normal biochemical processes are disrupted, leading to impairment or even cell death. The degree of injury is related to how much and how fast the axons get stretched. Ramesh’s team uses an experimentally characterized threshold at the point where the axons stretch more than 18 percent beyond their normal length.

Increasing Scrutiny

Concussion is a subset of a broader continuum of brain injuries known as mild traumatic brain injury, but even the experts diverge on exact classifications and the terms often are used interchangeably. For many experts, however, there is a distinction.

“A concussion is temporary,” says Daphalapurkar. “It’s when the brain has been rattled due to traumatic accelerations disrupting normal function. Mild traumatic brain injury, on the other hand, is a physical change in the brain in which the cells have been deformed to an extreme level.”

While terminology of brain injury is a matter of debate, the threat posed by such injuries is not. Concussion has come under increasing scrutiny in recent years fueled largely by concerns for the long-term mental and physical health of soldiers and million-dollar athletes who have sustained head trauma.