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


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


METHODS
Home recording.


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


METHODS
None.


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.
Child Development Center, University Children's Hospital Zurich, Switzerland ; Children Research Center, University Children's Hospital Zurich, Switzerland.
Sara
S
Fattinger
Child 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.
Oskar G
OG
Jenni
Children Research Center, University Children's Hospital Zurich, Switzerland ; Division of Clinical Neurophysiology, University Children's Hospital Zurich, Switzerland.
Bernhard
B
Schmitt
Institute 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.
Peter
P
Achermann
Child 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.
Reto
R
Huber
D004569:Electroencephalography; D005260:Female; D006706:Homeostasis; D006801:Humans; D007223:Infant; D008297:Male; D009474:Neurons / Q000502:physiology; D009778:Occipital Lobe / Q000166:cytology / Q000502:physiology; D012890:Sleep / Q000502:physiology*
Sleep; development; homeostasis; infants; slope of slow waves