Changes in brain network activity during working memory tasks: A magnetoencephalography study

Abstract

In this study, we elucidate the changes in neural oscillatory processes that are induced by simple working memory tasks. A group of eight subjects took part in modified versions of the N-back and Sternberg working memory paradigms. Magnetoencephalography (MEG) data were recorded, and subsequently processed using beamformer based source imaging methodology. Our study shows statistically significant increases in θ oscillations during both N-back and Sternberg tasks. These oscillations were shown to originate in the medial frontal cortex, and further to scale with memory load. We have also shown that increases in θ oscillations are accompanied by decreases in β and γ band oscillations at the same spatial coordinate. These decreases were most prominent in the 20-40 Hz frequency range, although spectral analysis showed that γ band power decrease extends up to at least 80 Hz. β/γ Power decrease also scales with memory load. Whilst θ increases were predominately observed in the medial frontal cortex, β/γ decreases were associated with other brain areas, including nodes of the default mode network (for the N-back task) and areas associated with language processing (for the Sternberg task). These observations are in agreement with intracranial EEG and fMRI studies. Finally, we have shown an intimate relationship between changes in β/γ band oscillatory power at spatially separate network nodes, implying that activity in these nodes is not reflective of uni-modal task driven changes in spatially separate brain regions, but rather represents correlated network activity. The utility of MEG as a non-invasive means to measure neural oscillatory modulation has been demonstrated and future studies employing this technology have the potential to gain a better understanding of neural oscillatory processes, their relationship to functional and effective connectivity, and their correspondence to BOLD fMRI.

Transient Suppression of Broadband Gamma Power in the Default-Mode Network Is Correlated with Task Complexity and Subject Performance

“…Compared to previous noninvasive studies based on scalp electroencephalography or magnetoencephalography (MEG) (Laufs et al, 2003;Mantini et al, 2007;Scheeringa et al, 2008;de Pasquale et al 2010;Brookes et al, 2011), the direct intracranial recordings used here allow for a higher spatial resolution particularly for deeper structures, and for the detection of electrophysiological correlates of the DMN at higher frequencies (up to 200 Figure 3. Single electrode data show suppression of gamma-band activity varies with task difficulty.…”

Abnormal MEG Oscillatory Activity during Visual Processing in the Prefrontal Cortices and Frontal Eye-Fields of the Aging HIV Brain

“…In particular, frontal theta activity has been linked to working memory and visual attention processes [40]–[42]. In addition, several studies have shown that frontal theta increases are correlated with memory load, in that larger memory loads (e.g., 5 items compared 3 items) are associated with stronger frontal theta activity [40]–[41], [43]–[44]. There is also some evidence that frontal alpha activity increases with memory load [42], although these reports have been less frequent.…”

Lifespan age differences in working memory: A two-component framework

“…Local increases in (frontal) theta have been observed in various memory and attention tasks during encoding, retention, and retrieval of information (e.g., Brookes et al, 2011;Gevins et al, 1997;Klimesch, 1999;Klimesch et al, 1996;Michels et al, 2008;Raghavachari et al, 2001;Sauseng et al, 2007;Sederberg et al, 2003), pointing to the involvement of frontal control processes in these tasks. WM load has been found to modulate frontal theta activity (Brookes et al, 2011;Jensen and Tesche, 2002). Furthermore, theta activity plays a major role in the integration of distributed neural information, such that interregional theta synchronization co-activates different brain regions (Sauseng et al, 2010).…”