Theta-gamma coupling during REM sleep depends on breathing rate

Area of Science:

• Neuroscience
• Computational Neuroscience
• Sleep Research

Background:

• Temporal coupling between theta and gamma oscillations is crucial for cortical network function, particularly during REM sleep.
• Nasal breathing generates phase-entrained oscillations that modulate gamma activity, but respiration and theta rhythms were considered largely independent.
• Previous research suggested both rhythms aid large-scale integration but differed in frequency and gamma modulation.

Purpose of the Study:

• To investigate the relationship between theta-gamma coupling and respiration during REM sleep in mice.
• To determine if respiration influences theta-gamma coupling beyond phase-entrainment.
• To explore potential differences in this relationship during distinct REM sleep states (phasic and tonic).

Main Methods:

• Electrophysiological recordings in mice during natural sleep.
• Analysis of theta and gamma oscillations during REM sleep.
• Correlation analysis between respiration rate and theta-gamma coupling strength.

Main Results:

• A robust, inverted V-shaped relationship was found between theta-gamma coupling strength and respiration rate.
• Maximal theta-gamma coupling occurred at breathing frequencies of 4-6 Hz.
• Breathing's relation to theta-gamma coupling differed between phasic and tonic REM sleep states.

Conclusions:

• Respiration rate, not just phase, significantly modulates theta-gamma coupling during REM sleep.
• This finding challenges the notion of theta and respiration as independent modulators of cortical activity.
• The results highlight a more complex interplay between respiratory and neural oscillations than previously understood.