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

Abstract

The objective of this preliminary study was to quantify changes in complexity of EEG using fractal dimension (FD) alongside linear methods of spectral power, event-related spectral perturbations, coherence, and source localization of EEG generators for theta (4-7 Hz), alpha (8-12 Hz), and beta (13-23 Hz) frequency bands due to a memory load effect in an auditory-verbal short-term memory (AVSTM) task for words. We examined 20 healthy individuals using the Sternberg's paradigm with increasing memory load (three, five, and seven words). The stimuli were four-letter words. Artifact-free 5-s EEG segments during retention period were analyzed. The most significant finding was the increase in FD with the increase in memory load in temporal regions T3 and T4, and in parietal region Pz, while decrease in FD with increase in memory load was registered in frontal midline region Fz. Results point to increase in frontal midline (Fz) theta spectral power, decrease in alpha spectral power in parietal region-Pz, and increase in beta spectral power in T3 and T4 region with increase in memory load. Decrease in theta coherence within right hemisphere due to memory load was obtained. Alpha coherence increased in posterior regions with anterior decrease. Beta coherence increased in fronto-temporal regions. Source localization delineated theta activity increase in frontal midline region, alpha decrease in superior parietal region, and beta increase in superior temporal gyrus with increase in memory load. In conclusion, FD as a nonlinear measure may serve as a sensitive index for quantifying dynamical changes in EEG signals during AVSTM tasks.

The role of alpha oscillations in distractor inhibition during memory retention

“…Interestingly, a wide range of recent studies report the involvement of beta oscillations in WM processes (Deiber et al ., ; Axmacher et al ., ; Siegel et al ., ; Johnson et al ., ; Spitzer & Haegens, ), although its specific role is still unclear. Increased beta activity during WM maintenance has been reported for WM tasks of different modalities: visual (Tallon‐Baudry et al ., , ), tactile (Spitzer et al ., ), auditory (Stokić et al ., ; Yu et al ., ) and temporal (Chen & Huang, ). Moreover, beta power increases with memory load (Leiberg et al ., ; Deiber et al ., ; Palva et al ., ; Honkanen et al ., ; Chen & Huang, ; Kornblith et al ., ).…”

Extraction of common task features in EEG-fMRI data using coupled tensor-tensor decomposition

“…It is well known that EEG sources with theta and alpha band activities are associated with workingmemory tasks (Debener et al 2005;Khader et al 2010;Dong et al 2015;Stoki et al 2015;Esposito et al 2009), therefore, both sensor and source-level EEGs were band-pass filtered to theta and alpha bands. Next, the EEGs were Hilbert enveloped, convolved with a canonical HRF (Glover 1999), and downsampled to the frequency of the fMRI recording (0.4545 Hz).…”

Analysis of the complexity of EEG during the short-term memory task

“…There is a study that applies complexity estimation to the assessment of the activity of the short-term memory [5]. This study shows that with the increase in memory load, fractal dimension value decreases in frontal region and increases in temporal regions and parietal regions.…”

“…As a result, fractal dimension analysis can reflect the activity of the working memory better than sample entropy analysis. Moreover, in order to investigate the relationship between the fractal dimension value and the power of theta band (4)(5)(6)(7)(8) in the frontal region, we conducted a correlation coefficient analysis. The result showed that increase of the power of theta band and decrease of fractal dimension value has relatively high correlation.…”