Resonance of human brain under head acceleration - Supplemental material

Although safety standards have reduced fatal head trauma due to single severe
head impacts, mild trauma from repeated head exposures may carry risks of
long-term chronic changes in the brain’s function and structure. To study the
physical sensitivities of the brain to mild head impacts, we developed the first
dynamic model of the skull–brain based on in vivo MRI data. We showed that
the motion of the brain can be described by a rigid-body with constrained kinematics.
We further demonstrated that skull–brain dynamics can be
approximated by an under-damped system with a low-frequency resonance at
around 15 Hz. Furthermore, from our previous field measurements, we found
that head motions in a variety of activities, including contact sports, show a primary
frequency of less than 20 Hz. This implies that typical head exposures may
drive the brain dangerously close to its mechanical resonance and lead to amplified
brain–skull relative motions. Our results suggest a possible cause for mild
brain trauma, which could occur due to repetitive low-acceleration head
oscillations in a variety of recreational and occupational activities.