Motor Activity and “Neotenic” Sleep in the Naked Mole Rat (Heterocephalus glaber) under Isolation

For the first time, continuous registration of motor activity and electroencephalogram for 40 days was carried out in four individuals of the naked mole rat (Heterocephalus glaber) in isolated conditions in the laboratory. A clear circadian rhythm of motor activity was found, with a gradual decrease during the night and an increase during the day, which remained both in the 12L/12D mode and in conditions of complete darkness. The rest states occupied, on average, about half the time of the day. There were both typical and atypical sleep periods, in which REM sleep episodes preceded NREM sleep periods. REM sleep percentage was unusually high (up to 50% of the total sleep time). During REM sleep episodes, a synchronized two-phase high-amplitude rhythm with a frequency of 12-16 Hz was recorded in the EEG. In addition, there were hard-to-identify periods of sleep, combining elements of both NREM and REM sleep. The sleep structure of naked mole rats resembles that of evolutionarily ancient species, as well as the "disorganized" sleep characteristic of the early stages of ontogenesis in altricial mammals.