Memory load effect in auditory-verbal short-term memory task: EEG fractal and spectral analysis

Area of Science:

• Neuroscience
• Cognitive Science
• Signal Processing

Background:

• Auditory-verbal short-term memory (AVSTM) tasks are crucial for cognitive function.
• Quantifying brain activity complexity during memory load is essential for understanding cognitive processes.
• Traditional linear EEG analysis methods may not fully capture dynamic changes in neural signals.

Purpose of the Study:

• To quantify changes in EEG complexity using fractal dimension (FD) during an auditory-verbal short-term memory (AVSTM) task.
• To compare FD with linear EEG measures (spectral power, coherence, source localization) under varying memory loads.
• To investigate the impact of memory load on theta, alpha, and beta frequency bands.

Main Methods:

• Utilized Sternberg's paradigm with 20 healthy individuals and increasing memory loads (3, 5, 7 words).
• Analyzed artifact-free EEG segments during the retention period.
• Applied fractal dimension (FD) analysis alongside spectral power, coherence, and source localization.

Main Results:

• Fractal dimension (FD) increased in temporal (T3, T4) and parietal (Pz) regions, but decreased in the frontal midline (Fz) with higher memory load.
• Significant changes in spectral power, coherence, and source localization were observed across different frequency bands and brain regions.
• FD demonstrated sensitivity to memory load-induced alterations in EEG dynamics.

Conclusions:

• Fractal dimension (FD) is a sensitive nonlinear measure for quantifying dynamic EEG changes during AVSTM tasks.
• FD complements linear EEG analysis methods in assessing cognitive load.
• Findings highlight the utility of FD in understanding neural correlates of memory.