The quantification of intrahemispheric EEG asymmetry in rat

We have developed a simple model to quantify the intrahemispheric asymmetries (IA) present in the background EEG activity (BEA), of the adult rat during restrained wakefulness and anesthesia with Ether and chloral hydrate (CHL). We used a collectivity of 40 adult (140 g) male Wistar rats. The epidural EEG activity, was quantified within the 1-30 Hz band by six numerical parameters: root mean square (RMS), mean spectral frequency (MSF), spectral edge frequency at 95% (SEF95) and the relative spectral power (RSP) within the Theta (4.5-7.5 Hz), Alpha (7.5-12 Hz) and Beta (12.5-30 Hz) bands. A significant IA was considerate when simultaneously present in both hemispheres at p (t-Test) < 0.05. The only IA detected in the BEA of the awake restrained rat was the increased theta RSP over the fronto-parietal areas. The theta asymmetry was abolished under both types of anaesthesia. While ether had a global effect on BEA, CHL induced a strong IA reflected in all parameters except RMS and Theta RSP. The fronto-parietal areas seem to be relatively resistant to CHL. It is discussed that the intrahemispheric theta dominance over the frontoparietal areas should be regarded as an indicator of alertness in rats.