Theta rhythm during REM sleep and waking: correlations between power, phase and frequency

Area of Science:

• Neuroscience
• Computational Neuroscience
• Electrophysiology

Background:

• The hippocampus generates theta oscillations crucial for cognitive functions.
• Understanding theta phase dynamics is key to deciphering neural coding during behavior.

Purpose of the Study:

• To investigate the dynamic relationship between theta phase and frequency in the rat hippocampus during REM sleep and active waking.
• To characterize the theta phase-frequency correlation in the CA1 stratum radiatum.

Main Methods:

• Recorded hippocampal electroencephalogram (EEG) in rats during REM sleep and active waking.
• Utilized Fourier analysis to assess time-varying theta power, frequency, coherence, and phase.
• Focused analysis on the CA1 stratum radiatum (apical dendritic layer).

Main Results:

• A significant positive correlation between theta phase and peak theta frequency was observed in the CA1 stratum radiatum during both REM sleep and active waking.
• Theta phase ranged from 100-170 degrees, approaching 180 degrees at higher frequencies (7.8-8.6 c/sec).
• Theta harmonic power, fast EEG power, and radiatum theta phase increased with increasing theta frequency.

Conclusions:

• Hippocampal theta phase and frequency are dynamically coupled during normal behaviors.
• These findings suggest the involvement of both atropine-sensitive and atropine-resistant inputs in regulating theta oscillations.
• The stratum radiatum plays a specific role in this phase-frequency relationship.