Interhemispheric differences in awake and sleep human EEG: a comparison between non-linear and spectral measures

Area of Science:

• Neuroscience
• Physiology
• Signal Processing

Background:

• Electroencephalography (EEG) is crucial for studying brain activity.
• Interhemispheric EEG differences provide insights into hemispheric specialization.
• Non-linear dynamics offer advanced methods for EEG analysis.

Purpose of the Study:

• To investigate interhemispheric EEG differences in healthy adults.
• To compare spectral and non-linear EEG measures between hemispheres.
• To analyze EEG complexity and predictability across sleep stages.

Main Methods:

• EEG recordings from C3 and C4 derivations in nine healthy right-handed subjects.
• Analysis of harmonic power spectral density across standard EEG bands.
• Calculation of fractal dimension (Dr), correlation dimension (D2), and largest Lyapunov exponent (lambda1).
• Comparison of measures during resting wake (closed eyes) and sleep stages I, II, III, IV, and REM.

Main Results:

• Interhemispheric differences in fractal dimension, correlation dimension, largest Lyapunov exponent, and alpha band power were observed during waking.
• Right hemisphere (RH) generally showed higher values than the left hemisphere (LH), except for lambda1.
• Non-linear parameters (D2, lambda1) revealed reversed asymmetries during slow wave sleep (SWS) compared to waking and lighter sleep stages.
• Negative correlations were found between D2, lambda1 and delta band power; positive correlations between lambda1 and alpha/beta band power.

Conclusions:

• The RH is more complex and predictable than the LH during resting wake and early sleep stages (I, II).
• EEG complexity and predictability patterns shift, favoring the LH during SWS.
• Non-linear EEG measures reveal dynamic hemispheric changes across different behavioral states.