Sleep architecture in unrestrained rhesus monkeys (Macaca mulatta) synchronized to 24-hour light-dark cycles

Abstract

Study objectives: To characterize the sleep patterns of unrestrained, diurnal nonhuman primates entrained to 24-hour light-dark cycles. Design: EEG, EMG, and EOG were recorded continuously via implanted telemetry from 5 unrestrained male rhesus monkeys housed individually under a 16:8 light-dark cycle (LD 16:8; L = 13 lux; D = 0 lux). Results: In a LD 16:8 cycle, all 5 monkeys demonstrated a long period of consolidated sleep during the 8-h dark period. On average, sleep accounted for 89.2% of the 8-h dark period and 25.2% of the 16-hour light period. REM sleep occupied 23% of total sleep time over 24 h, or 10.7% of the total time. The average length of the consolidated sleep (CS) period was 10.5 h, although the time of CS onset was variable. In contrast, the end of CS, and thus the onset of consolidated wakefulness (CW) demonstrated very little variation, typically occurring within 2 min of light onset. Ultradian NREM-REM cycles with periods of approximately 60 min were also observed. EEG delta activity during NREM sleep, thought to reflect the homeostatic sleep process, peaked at 3-4 h after CS onset. Conclusions: The present study demonstrates the feasibility of long-term, unrestrained sleep monitoring in nonhuman primates using fully-implantable biotelemetry. With minor exceptions, most notably a delay in peak delta activity, sleep-wake architecture, regulation, and consolidation in rhesus monkeys strongly resembles that of humans. These results demonstrate that the unrestrained rhesus monkey is an excellent biomedical model for human sleep.