Study on Different Brain Activation Reorganization during Cognitive Load: ERD/ERS and Coherence Analysis

Academic Background

When humans engage in imagination, movement, or cognitive tasks, their brain functional activity patterns and activated regions differ. These pattern changes are also reflected in changes in brain electrical activity, which can be measured from the scalp using electroencephalography (EEG). Cognitive tasks lead to relative changes in EEG signal patterns, namely Event-Related Desynchronization/Synchronization (ERD/ERS). This study aims to explore brain activation patterns while performing mental arithmetic tasks, particularly by calculating the power spectral density (PSD) of EEG signals and conducting coherence analysis to reveal these patterns.

Study Source

This paper was written by Md. Rayahan Sarker Bipul, Md. Asadur Rahman, and Md. Foisal Hossain, from Khulna University of Engineering and Technology (KUET) and Military Institute of Science and Technology (MIST), respectively. The study was received on September 21, 2022, revised on July 11, 2023, accepted on November 4, 2023, and published in the journal “Cognitive Neurodynamics” under Springer Nature.

Study Procedure

Data Collection and Experimental Design

This study used EEG data related to mental arithmetic tasks collected from the PhysioBank database (https://archive.physionet.org/physiobank/database/eegmat/). A total of 66 participants, all right-handed healthy individuals aged between 18 and 26 years, participated. EEG data were recorded using a 23-channel system, with a sampling rate of 500 Hz, and electrodes were arranged according to the international 10-20 system.

The experimental design was divided into three stages: adaptation period, resting period, and mental arithmetic period. Participants sat quietly for three minutes during the resting period, followed by a four-minute mental arithmetic task, with data recorded from the first three minutes of the task.

Data Processing and Analysis Methods

Data preprocessing was conducted using the Matlab programming language. The mental arithmetic task involved a series of subtractions of two-digit numbers from four-digit numbers. Common artifacts in EEG signals (such as muscle noise) were removed appropriately. Participants were required not to use any limb movements and to complete the tasks through imagination alone.

Data analysis included calculating ERD/ERS and coherence. ERD/ERS analysis was performed by computing the power spectral density (PSD) using the Welch method, and coherence analysis was conducted to verify the ERD/ERS results.

Key Results

ERD/ERS Analysis

The study found significant changes in the power of theta and beta frequency bands in EEG signals during mental arithmetic tasks. Notably, these changes in brainwave frequency band power were mainly concentrated in the left hemisphere. As the complexity of the task increased, the relative amount and duration of ERD/ERS also increased. ERD/ERS analysis showed synchronization and desynchronization changes in different brain regions during cognitive tasks.

Coherence Analysis

Coherence analysis verified the results of ERD/ERS analysis, showing changes in the synchronization of electrical activity in different brain regions within specific frequency ranges during cognitive tasks. The amount of ERS in the left hemisphere increased during mental arithmetic tasks, while the right hemisphere also showed asymmetric distribution of relative ERD/ERS in the prestimulus phase.

Conclusion and Value

This study reveals brain activation patterns and regional distribution during cognitive tasks through ERD/ERS and coherence analysis. These results not only help understand the functional reorganization process of the brain during complex cognitive tasks but also provide a foundation for future research, especially in the fields of cognitive neuroscience, mathematical skill development, and brain-computer interface applications.

Research Highlights

1. Combined ERD/ERS and Coherence Analysis: This study is the first to combine ERD/ERS and coherence analysis methods to study EEG activity during mental arithmetic tasks.
2. Regional Distribution of Brain Functional Reorganization: The study provides a detailed description of synchronization and desynchronization changes in different brain regions during cognitive tasks, offering a more precise brain function map.
3. Broad Application Prospects of Data: The research results provide important references for future applications in cognitive neuroscience, education, and brain-computer interface development fields.

Conclusion

Through ERD/ERS and coherence analysis, this study reveals in detail the functional activation patterns and regional distribution of the brain during complex cognitive tasks (such as mental arithmetic). The results indicate that combined ERD/ERS and coherence analysis is an effective method that can provide reliable information on brain functional states during cognitive tasks. These findings not only contribute to a deeper understanding of brain functional reorganization mechanisms but also promote future applications in cognitive neuroscience and brain-computer interface research.