Impedance Changes in the Cerebrum Following Concussion. ∗

Since cellular injury is associated with impairment of cellular surface membranes (Osterhout 1 ), it seems reasonable to surmise that cerebral concussion produces similar changes in the cerebrum. The electrocortico-gram does not permit definite conclusions (Walker, Kollros, and Case 2 ) regarding the cellular surface films, since other factors may affect it. We approached this problem by measuring the A.C. impedance of the cerebral hemispheres in 14 cats in vivo and in 50 guinea pigs immediately post mortem, at a low frequency (1 = 570 cycles per second) and a high frequency (h = 5100 cycles), and computing

δ is a measure of the polarizability. In agreement with Gildemeister's 3 theory, we have given experimental evidence on artificial membranes and frog skin (Spiegel and Spiegel-Adolf 4 ) that decrease of polarizability is associated with increase of electrolyte permeability. Acceleration concussion (Denny-Brown and Russell 5 ) was produced by means of a pendulum, under nembutal anesthesia.

Results. In control experiments on cats δ remained constant for at least 2 hours when the experimental conditions were identical except for omission of the blow. Blows inducing signs of concussion, typical changes of blood pressure, transitory apnea, loss of the corneal-, light-, pinna reflex, induced a mean decrease of δ of 23.4 ± 1.6%. Usually it became most marked within 1/2-1 hour after the blow. Then a slow rise of δ from the minimum began to develop. However, 4 hours after the blow a definite decrease of δ was still noticeable. These changes of δ did not appear if the pendulum struck a dead animal. It should be emphasized that the decrease of δ developed independently of the fluctuations of conductivity, which were too irregular to permit definite conclusions.

Since in these experiments the skull had to be trephined for introduction of the electrodes before concussion, these measurements were repeated in guinea pigs concussed with the skull intact.