New findings on sleep stage organization in squirrel monkeys

The EEGs of 11 squirrel monkeys were studied during nocturnal sleep under conditions maintaining relative freedom of movement and minimal social intercourse. For the amount and partition of the different sleep stages, the present findings markedly differ from previous observations in experimental restrained conditions. Six sleep stages were defined by both EEG and spectral analysis criteria. Wakefulness, which occurred during the first period of the night, was more abundant (45%) and deep sleep (SIII) and REM sleep were less abundant (SIII: 5.1%; REM: 3.1%) in unrestrained squirrel monkeys. With predominant light sleep (85%), less abundant deep sleep and a REM sleep organization in short episodes, the sleep pattern in this New World monkey appeared fragmented and close to African monkey sleep.