Abstract
We employed spectral Granger causality analysis on a full set of 56 electroencephalographic recordings acquired during the execution of either a 2D movement pointing or a perceptual (yes/no) change detection task with memory and non-memory conditions. On the basis of network characteristics across frequency bands, we provide evidence for the full dissociation of the corresponding cognitive processes. Movement-memory trial types exhibited higher degree nodes during the first 2 s of the delay period, mainly at central, left frontal and right-parietal areas. Change detection-memory trial types resulted in a three-peak temporal pattern of the total degree with higher degree nodes emerging mainly at central, right frontal, and occipital areas. Functional connectivity networks resulting from non-memory trial types were characterized by more sparse structures for both tasks. The movement-memory trial types encompassed an apparent coarse flow from frontal to parietal areas while the opposite flow from occipital, parietal to central and frontal areas was evident for the change detection-memory trial types. The differences among tasks and conditions were more profound in α (8–12 Hz) and β (12–30 Hz) and less in γ (30–45 Hz) band. Our results favor the hypothesis which considers spatial working memory as a by-product of specific mental processes that engages common brain areas under different network organizations.
Highlights
Understanding the mechanisms that pertain to the function of working memory (WM) is a fundamental and still open problem in neuroscience
The color of the circle was either blue indicating that the trial would be completed by making a pointing movement, or red indicating that the trial would be completed by pressing one of two buttons giving a yes/no response
As we described in a previous study (Smyrnis et al, 2014), the behavioral criteria that leaded to trial-rejection were: (1) reaction time below 100 ms or above 1500 ms and/or cursor exiting the center target at any time during baseline, target presentation and delay period; (2) directional error for the final endpoint of the movement more than 30◦ clockwise or counter clockwise from the direction of the peripheral target and distance error larger than 60 pixels (1.4 inches) from the center of the peripheral target either overshooting or undershooting the peripheral target; (3) no button press after the “go” signal
Summary
Understanding the mechanisms that pertain to the function of working memory (WM) is a fundamental and still open problem in neuroscience. WM processing is considered to be governed by two functions, namely the phonological loop, and the visuo-spatial sketchpad (Baddeley and Hitch, 1974). Various studies have shown that the visuo-spatial sketchpad can be further separated depending on the task (“what” and “where” pathways) (Goodale et al, 1994). It has been shown that the mechanism of visuospatial WM retains complete motor programs that could either be executed or not (Awh and Jonides, 2001).
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