Sleep in the blind mole rat Spalax ehrenbergi

Abstract

Study Objectives: The mole rat, Spalax ehrenbergi, is an interesting species for sleep because of its pronounced specialization to a fossorial life. These rodents spend most of their life-time underground, and are less exposed to many of the environmental stimuli and challenges that are common to non-fossorial rodents. A prominent adaptation is their blindness, which is due to an atrophy of the eyes. Design: Continuous 24-h recordings of EEG, EMG and cortical temperature, and EEG spectral analysis were performed in six individuals caught in the wild and adapted to the laboratory for several months. Setting: N/A. Patients or Participants: N/A. Interventions: N/A. Measurements and Results: Total sleep time (52% of recording time) and the amount of REM sleep (8% of recording time) in these subterranean rodents are in the range of values found in the laboratory rat, mouse and hamster recorded under similar conditions. In contrast to these species, the polyphasic sleep-wakefulness distribution in mole rats was more distinct. A predominance of sleep in the dark period was only minor and not present in all individuals, which resembles sleep in the guinea pig. As in all other mammals investigated, the daily time course of EEG slow-wave activity (SWA) in nonREM sleep closely followed the polyphasic sleep-wake pattern and the light-dark preference. The transitions from non REM sleep to REM sleep were characterized, as in other rodents, by a gradual increase in EEG activity in the theta and sigma frequency bands before the transition. However, the power surge in these frequencies massively exceeded that found in other rodents. This feature may be related to adaptations of the brain to the requirements of the subterranean habitat. Conclusions: It is remarkable that large ecological differences between species within the same order have relatively small effects on many sleep features. The time course of SWA confirmed its predictability on the basis of the previous sleep-wake history.