Spectral analysis of the electroencephalographic response in experimental concussion in the rat

The phenomenon of concussion was studied in 32 non-anesthetized Sprague-Dawley male rats, previously implanted with chronic epidural electrodes for bipolar recording of the electroencephalogram (EEG). EEG records were taken continuously preceding during and following concussion, which was produced by a lead-tipped dart, shot from a spring-loaded pistol. The mass and velocity of the striking instrument were measured, so that its momentum and kinetic energy could be calculated. Spectral analysis of the EEG was performed by means of computer, using Fast Fourier Transform. In stage 1-2 of concussion, the power spectra of alpha, beta, and theta frequency bands were decreased by 25%, 37% and 10%, respectively. The delta spectrum alone was increased by 15%. Stage 3-4 of concussion was characterized by more profound depression of the power spectra of alpha, beta, theta and delta frequency bands (56%, 49%, 34% and 31%, respectively). EEG depression occurred immediately, reached a peak at 5 min and recovered at an average of 2 h in the concussed rats. In 5 rats, which did not recover completely, post-mortem examination revealed cerebral contusion or intracranial hematomas. These rats were not included in the analysis of 'concussion'. The EEG changes suggest the involvement of the cerebral cortex in the traumatic unconsciousness of concussion and are similar to those of spreading depression, as noted by previous investigators.