The slow and infraslow oscillations of cortical neural network

-Goran Keković, Slobodan Sekulić, Jelena Podgorac, Jelena Mihaljev-Martinov, Ksenija Gebauer-Bukurov

Disclaimer: The content below was generated with the assistance of AI and then reviewed and edited by BrainMaster Technologies, Inc. It is provided for educational and informational purposes only and does not constitute medical advice.

Overview

This document examines the characteristics and functional significance of slow (delta) and infraslow oscillations (ISOs) in human EEG recordings. Researchers evaluated their behavior in epileptic seizures (general and focal) and in healthy individuals performing motor and mental tasks. The findings highlight how ISOs may influence cortical network synchronization and contribute to both normal and pathological brain activity.

1. Background #

1.1 Role of Low-Frequency Brain Activity #

Prior studies have shown elevated delta activity during epileptic discharges. However, ISOs (<0.1 Hz) have been less explored due to technical challenges.
The article reviews emerging research suggesting that slow rhythms may regulate communication between brain regions, potentially modulating higher-frequency bands.

2. Methods #

2.1 Participants and EEG Data #

• Three groups (N=23 each):

  • Generalized epileptic seizures

  • Focal epileptic seizures

  • Healthy volunteers performing motor imagery and movement tasks

• EEG duration: 1 minute per recording

• Sampling: 256 Hz (patients), 160 Hz (healthy)

• Tasks for healthy participants included fist and foot movements/imagery.

2.2 Signal Processing #

• Artifact removal via Singular Value Decomposition / ICA

• Resampling to 10 Hz for detailed analysis of the 0–4 Hz range

• Power spectral density estimated via Yule–Walker AR modeling

• Spectral coherence computed to evaluate functional coupling between brain regions

3. Key Findings #

3.1 Epileptic Seizures #

• Prominent peak at 1.5 Hz in both generalized and focal seizures.

• Generalized seizures showed pronounced ISOs at ~0.05 Hz, visible in rhythmic patterns (20-second cycles), suggesting large-scale network synchronization.

• Focal seizures featured the 1.5 Hz peak but lacked clear ISO rhythmic modulation.

3.2 Healthy Participants #

• Power spectra lacked distinct ISO peaks, but spectral coherence analysis revealed periodic modulation at 0.05 Hz, indicating ISOs influence inter-regional connectivity even without strong amplitude expression.

3.3 Statistical Results #

• PSD at 1.5 Hz significantly higher in:

  • Generalized seizures vs. healthy

  • Focal seizures vs. healthy

  • Generalized vs. focal seizures

• Spectral coherence (1–2 Hz):

  • Much lower in epileptic groups, suggesting disrupted long-range neural synchronization.

  • Healthy subjects displayed high coherence, with recurring 0.05-Hz modulation.

4. Interpretation #

4.1 Significance of Infraslow Oscillations #

• ISOs may contribute to large-scale cortical network synchronization.

• They appear to modulate delta and higher-frequency activity, shaping both normal task-related brain dynamics and pathological states.

• Generalized seizures likely involve widespread cortical ISO fluctuations, while focal seizures may not.

4.2 Implications for Epilepsy Research #

• Findings support hypotheses that ISOs could influence seizure generation, especially in generalized types.

• Coherence abnormalities could serve as potential biomarkers for epileptic network dysfunction.

5. Conclusion #

The study demonstrates that infraslow oscillations are fundamental components of cortical activity, influencing both healthy brain function and epileptic conditions. ISOs, particularly at 0.05 Hz, appear to play a key role in long-range synchronization and may interact with delta activity during seizures. Further research is needed to clarify the mechanisms and clinical applications of ISO-related brain dynamics.