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Published on: August 2, 2017
Homeostatic coupling of cortical and brainstem delta rhythms in sleeping infant rats
Midha Ahmad1, Greta Sokoloff1,2, Mark S Blumberg1,2
1Department of Psychological & Brain Sciences, University of Iowa, Iowa City, IA 52242 USA.
Insights
Brain delta rhythms in infant rats remain coupled between the cortex and medulla during sleep and altered breathing. This synchrony highlights the interconnectedness of sleep regulation and respiration during development.
Area of Science:
- Neuroscience
- Developmental Neuroscience
- Sleep Research
Background:
- The emergence of cortical delta rhythm (1-4 Hz) during quiet sleep (QS) is a key developmental milestone in infant rats, typically occurring between postnatal days 8-12.
- Previous research indicated age-dependent increases in medullary (Pons-Medulla or PZ) delta-rhythmic activity synchronized with cortical delta and influenced by breathing.
Purpose of the Study:
- To investigate if the long-distance synchrony between cortical and medullary delta rhythms persists under conditions of altered sleep homeostasis and respiration.
- To examine the coupling strength between frontal cortex and PZ delta rhythms in response to sleep deprivation and mild hypercapnia in infant rats.
Main Methods:
- Utilized male and female postnatal day 12 (P12) rats for experiments.
- Administered a short period of intense sleep deprivation followed by recovery sleep.
- Introduced mild hypercapnia (5% CO2) to manipulate breathing patterns.
- Analyzed phase-locking and lagged cross-correlation to assess temporal coupling between cortical and medullary delta rhythms.
Main Results:
- Sleep deprivation led to a rebound in delta power in both the PZ and cortex during recovery sleep, indicating their roles as equivalent markers of homeostatic sleep regulation.
- Persistent temporal coupling was observed between cortical and PZ delta rhythms, with cortical delta reliably lagging PZ delta, irrespective of sleep pressure changes.
- Mild hypercapnia decreased delta power in both regions and reduced breathing depth, suggesting a link between respiratory function and delta rhythm generation.
- Observed an increase in breathing depth during recovery sleep post-sleep deprivation.
Conclusions:
- The delta rhythm in infant rats is coupled across distant brain regions (cortex and medulla), functioning as interconnected components of a developing sleep-homeostatic system.
- This delta rhythm is intimately linked with the brainstem respiratory network, as evidenced by its modulation by breathing alterations.
- The findings reinforce the strong coupling between cortical and medullary delta rhythms and deepen the understanding of the interplay between sleep rhythms and respiration during development.
Abstract:
The emergence of the cortical delta rhythm (1-4 Hz) during quiet sleep (QS) is a major milestone in brain development. In rats, this milestone is achieved between 8 and 12 days of postnatal (P) age. We previously reported an age-dependent increase in PZ delta-rhythmic activity that is synchronized with cortical delta and entrained by breathing. Here, we ask whether this long-distance synchrony persists in response to perturbations to sleep homeostasis or respiration. First, using male and female P12 rats, we investigated the coupling strength between frontal cortex and PZ in response to a short but intense period of sleep deprivation. During recovery sleep, we observed a rebound in delta power in both PZ and cortex, even in the absence of increased QS duration, indicating that PZ and cortical delta power are equivalent markers of homeostatic sleep regulation. Analyses of phase-locking and lagged cross-correlation revealed persistent temporal coupling between the two rhythms such that cortical delta reliably lagged PZ delta regardless of changes in sleep pressure. Curiously, we also observed an increase in breathing depth during recovery sleep, which we confirmed in a separate cohort of pups. Next, using mild hypercapnia (5% CO2) to alter breathing frequency and depth, we produced decreases in cortical and PZ delta power along with decreases in the depth of breathing. These findings provide additional support for the notion that PZ and cortical delta rhythms function as distantly interconnected components within a developmentally emerging sleep-homeostatic system that is also intimately tied with the brainstem respiratory network.
