G-force induced alterations in rat EEG activity: a quantitative analysis.

A major physical limitation affecting pilots is G-force (+Gz, head-to-foot inertial load) induced loss of consciousness. Previous studies have shown that +Gz produces qualitatively similar effects on human and rat EEG activity. The present study sought to quantitatively correlate changes in rat EEG activity with increasing +Gz levels. A frontal-parietal differential electrode recorded rat EEG data during +Gz exposures (30 s) ranging from +0.5 to +25.0 Gz. Acceleration levels < or = +10 Gz had little effect on EEG activity. Acceleration levels of +15 to +20 Gz were associated with increased EEG slowing, depression and sharp waves. Acceleration levels > or = +17.5 Gz evoked burst suppression followed by isoelectric activity. Times to first onset of delta, depressed, and isoelectric EEG activity were approximately 12, 14 and 18 s, respectively. Acceleration effects on delta (1-4 Hz), theta (5-8 Hz), alpha (9-12 Hz), beta (13-30 Hz) and total (1-30 Hz) EEG powers were examined using Fourier transform analysis. EEG measures with the most predictive value at the following post-acceleration onset times (PAOT) were as follows (in s); increasing theta power: PAOT 0-2, decreasing delta power: PAOT 3-9, and decreasing beta power: PAOT > or = 12. This study provides a quantitative description of +Gz-induced alterations in EEG magnitude, time course and spectral content. Additionally, several EEG measures were identified which correlated with acceleration level at specific post-acceleration onset times.