Aim: 

To recognize the presence of Brain EEG asymmetries in sleeping rats and the existence of interhemispheric dominance changes between day and night

Methods: 

The frontal and parietal EEG of five Wistar male rats (250-350 g) has been studied during 48 h of continuous recoding. In addition, the behavior was video recorded. Several 30 s EEG segments were selected from each animal. The EEG power in: delta (0.5-4 Hz), theta (4-8 Hz), alpha 1 (8-13 Hz), alpha 2 (13-15 Hz), and beta (25-30 Hz) bands has been calculated using the Fast Fourier Transform. Total EEG power was also analyzed. The Asymmetry Index (AI) was obtained from the resulting values.

Results: 

A significant population asymmetry, with right side dominance, was found in the total EEG power but the AI changed when light and dark time recordings were compared. No population asymmetry was found between spectral EEG bands, although evident asymmetries were observed in each animal. Then, the dominant sides of every animal were joined together, irrespective of having been recorded from left or right hemisphere, rendering an averaged AI for each electrode and recording time. Significant interhemispheric differences were observed in all frequency bands. Additional differences in AI were observed when comparing day and night recordings, with the highest AI being observed during light time.

Conclusion: 

Considering that most sleeping periods occur in the rat during light time, small but significant increases in brain asymmetry occur during sleep. Hence, asymmetric sleep could also exist in rats.