Effect of SCN lesions on sleep in squirrel monkeys: evidence for opponent processes in sleep-wake regulation

Mar 1, 1993The Journal of neuroscience : the official journal of the Society for Neuroscience

How damage to the brain's internal clock affects sleep in squirrel monkeys: signs of opposing processes controlling sleep and wakefulness

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Abstract

Total sleep time increased by 4.0 hours in SCN-lesioned monkeys compared to intact monkeys.

The suprachiasmatic nuclei (SCN) may actively promote wakefulness rather than merely gating sleep processes.
In SCN-lesioned monkeys, sleep-wake and sleep-stage patterns were disrupted, leading to increased total sleep time.
Deeper stages of non-REM sleep and REM sleep were not significantly affected by SCN lesions.
Wake bout lengths were significantly shorter in SCN-lesioned monkeys (15 +/- 6 min) compared to intact monkeys (223 +/- 10 min).
These findings suggest that the SCN plays a role in regulating daily sleep and wake times in diurnal primates.

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Sleep and wakefulness are governed by both the suprachiasmatic nuclei of the hypothalamus (SCN), and a sleep homeostatic process; however, the interaction of these control systems is not well understood. From rodent studies it has been assumed that the SCN promote neither wake nor sleep but gate the homeostatic sleep-promoting process. Yet in humans sleep tendency is lowest during the later waking hours of the day, and sleep duration can be predicted because of the precise circadian timing of waking. Thus in primates, the SCN could assure sleep-wake cycle consolidation by actively promoting or facilitating wakefulness. To evaluate this hypothesis, we examined the sleep-wake and sleep-stage patterns of intact and SCN-lesioned (SCNx) squirrel monkeys maintained in constant light. This diurnal primate has consolidated sleep and wake patterns more similar to man than rodents. Sleep-wake, sleep stages, brain temperature, and drinking circadian rhythms were eliminated, and total sleep time was significantly increased (4.0 hr, P < 0.01) in SCNx monkeys. However, total times in deeper stages of non-rapid eye movement (non-REM; e.g., delta sleep) and REM sleep were not significantly affected by SCN lesions. Increased total sleep time was associated with a reduction in subjective day wake consolidation, as evidenced by substantially shorter wake bout lengths in SCNx monkeys (15 +/- 6 min) as compared to intact monkeys (223 +/- 10 min; P < 0.0001, ANOVA). These findings show that the SCN influence the regulation of daily total wake and sleep times, and implicate an alternative sleep-wake regulatory model in which an SCN-dependent process actively facilitates the initiation and maintenance of wakefulness and opposes homeostatic sleep tendency during the subjective day in diurnal primates.

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Effect of SCN lesions on sleep in squirrel monkeys: evidence for opponent processes in sleep-wake regulation

Abstract

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