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Sleep. 2014 Feb 1;37(2):245-53. doi: 10.5665/sleep.3390.

Overnight changes in the slope of sleep slow waves during infancy.

Author information

  • 1Child Development Center, University Children's Hospital Zurich, Switzerland ; Children Research Center, University Children's Hospital Zurich, Switzerland.
  • 2Child Development Center, University Children's Hospital Zurich, Switzerland ; Children Research Center, University Children's Hospital Zurich, Switzerland ; Zurich Center for Integrative Human Physiology, University of Zurich, Zurich, Switzerland.
  • 3Children Research Center, University Children's Hospital Zurich, Switzerland ; Division of Clinical Neurophysiology, University Children's Hospital Zurich, Switzerland.
  • 4Institute of Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland ; Zurich Center for Integrative Human Physiology, University of Zurich, Zurich, Switzerland ; Neuroscience Center Zurich (ZNZ), University of Zurich, Zurich, Switzerland.
  • 5Child Development Center, University Children's Hospital Zurich, Switzerland ; Children Research Center, University Children's Hospital Zurich, Switzerland ; Zurich Center for Integrative Human Physiology, University of Zurich, Zurich, Switzerland ; Neuroscience Center Zurich (ZNZ), University of Zurich, Zurich, Switzerland.

Abstract

STUDY OBJECTIVES:

Slow wave activity (SWA, 0.5-4.5 Hz) is a well-established marker for sleep pressure in adults. Recent studies have shown that increasing sleep pressure is reflected by an increased synchronized firing pattern of cortical neurons, which can be measured by the slope of sleep slow waves. Thus we aimed at investigating whether the slope of sleep slow waves might provide an alternative marker to study the homeostatic regulation of sleep during early human development.

DESIGN:

All-night sleep electroencephalography (EEG) was recorded longitudinally at 2, 4, 6, and 9 months after birth.

SETTING:

Home recording.

PATIENTS OR PARTICIPANTS:

11 healthy full-term infants (5 male, 6 female).

INTERVENTIONS:

None.

MEASUREMENTS AND RESULTS:

The slope of sleep slow waves increased with age. At all ages the slope decreased from the first to the last hour of non rapid-eye-movement (NREM) sleep, even when controlling for amplitude differences (P < 0.002). The decrease of the slope was also present in the cycle-by-cycle time course across the night (P < 0.001) at the age of 6 months when the alternating pattern of low-delta activity (0.75-1.75 Hz) is most prominent. Moreover, we found distinct topographical differences exhibiting the steepest slope over the occipital cortex.

CONCLUSIONS:

The results suggest an age-dependent increase in synchronization of cortical activity during infancy, which might be due to increasing synaptogenesis. Previous studies have shown that during early postnatal development synaptogenesis is most pronounced over the occipital cortex, which could explain why the steepest slope was found in the occipital derivation. Our results provide evidence that the homeostatic regulation of sleep develops early in human infants.

KEYWORDS:

Sleep; development; homeostasis; infants; slope of slow waves

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