High-Density EEG Recordings in the European Jackdaw (Coloeus monedula): Sleep Deprivation Increases Nrem Sleep Time and Eeg Power While Reducing Hemispheric Asymmetry

Introduction: Sleep is a wide-spread phenomenon that is thought to occur in all animals. Mammals and birds have similar sleep states, yet there are large differences in sleep regulation between these taxonomic groups. One reason might be that the avian brain has a more nuclear organisation rather than the laminar mammalian brain. Yet, it is not known what the regional differences are in sleep regulation over the avian cortex. Therefore, we studied sleep architecture and sleep homeostatic responses to sleep deprivation using high-density electroencephalogram (EEG) in the European jackdaw (Coloeus monedula).

Materials and Methods: A total of nine young adult birds were implanted with 28 epidural electrodes and equipped with miniature data loggers for recording movement activity (accelerometery) and EEG. Individually-housed jackdaws were recorded under controlled conditions with a 12:12-h light-dark cycle. Every individual underwent two 3-day recordings that contained a 4 or 8 hour sleep deprivation starting from lights off on the second night in a randomized order.

Results: Jackdaws showed a homeostatic response to sleep deprivations of 4 and 8 hours in a dose-dependent manner for both NREM and REM sleep time. After both sleep deprivations, all 28 derivations showed a similar bi-modal increase in relative NREM sleep spectral power over a broad-range of frequencies (1.5-25 Hz) with peaks at 2.5 and 12.5 Hz. The lower frequencies were most pronounced in the posterior electrodes whereas the higher frequencies were most pronounced in the anterior electrodes. While there was little true unihemispheric sleep in the jackdaws, there was a certain degree of hemispheric asymmetry in NREM sleep EEG power during baseline, which reduced after sleep deprivation in a dose-dependent manner. This increased symmetry between the electrodes after sleep deprivation reflects that sleep need promotes synchrony in spectral EEG power between hemispheres.

Conclusions: Jackdaws have a clear homeostatic response to sleep deprivation in both sleep time and sleep EEG spectral power. Even though the entire cortex shows a relative similar response to sleep deprivation, there are regional differences in NREM sleep EEG power for certain frequencies. Importantly, the amount of lateralization was reduced during recovery. Together, this study shows the heterogeneity of the avian cortex in sleep regulation.