We hypothesize that an insight into brain injury during hypoxiaasphyxia and recovery can be gained by quantifying the changes in the frequency characteristics of EEG using auto-regressive (AR) modeling. Neonatal piglets (1-2 weeks old) are exposed to a sequence of 30 min hypoxia, 5 min room air, and 7 min asphyxia followed by a 4 h recovery period. Continuous 2-channel cortical EEG is recorded throughout. Overlapping EEG segments (3.3 sec segments, 2.6 sec overlap) are analyzed. Frequencies of peaks (3, in the bands 1-4 Hz, 8-12 Hz and 19-22 Hz), peak amplitudes, and power of each peak are obtained. Preliminary analysis (n = 4) shows that hypoxia affects the highest frequency component most, whereas the recovery of brain functions is reflected best in the lowest frequency component. Power in all 3 frequencies goes to approximately 0 in 40-60 sec of asphyxia. The recovery of power in all components begins 5-10 min after successful resuscitation efforts with a burst suppression pattern, and continuous activity is observed after 30-45 min. The average rate of recovery in the total power varies from 2.5 to 40% of baseline/h. Thus, AR modeling may be useful in quantitating the brain function in response to a hypoxic-asphyxic insult.