Investigators have been studying the mechanical phenomena associated with impact to the head for many years. Several theories on the behavior of the brain during head impact have come from these studies but there has been a notable lack of information on the bulk mechanical properties of the brain which are necessary for the evaluation of these theories. This paper represents an initial attempt at providing such information.

The dynamic complex shear modulus of in vitro samples of human brain have been measured. Specimens from eight brains have been subjected to a sinusoidal shear stress input under resonant conditions in an electro-mechanical test device. Tests were conducted to determine the effects of time after death, refrigeration of material and shear strain dependence. A device to measure the dynamic properties of brain in vivo is described and preliminary data on in vivo tests on Rhesus monkeys is presented.

The results of the dynamic shear testing on in vitro human brain indicate that the storage modulus G′ lies between 6–11 × 10³ dyn/cm², the loss modulus G″ lies between 3·5–6·0 × 10³ dyn/cm² and the loss tangent tan δ is in the range 0·40-0·55.