Human cortical responses to feed-back stimuli in visuomotor working memory and no working memory tasks: A high resolution EEG study

Introduction. Gevins' high resolution electroencephalographic (EEG) studies in humans have shown that central executive function of working memory involves a distributed system including several cortical frontoparietal areas of both hemispheres (1). In the present study, EEG rhythms were investigated to elucidate the cortical processing of visual feed-back during working memory (WM) and no working memory (NOWM) tasks. Methods. EEG (128 ch) was recorded in 3 right-handed, informed, normals. The WM task consisted of sequential right finger movements on a keyboard according to a cue visual stimulus (numbers). A visual stimulus (numbers) provided feed-back on performance accuracy. In the NOWM task, cue stimulus was available up to feed-back stimulus delivery. Artifact-free EEG trials were Laplacian transformed over a realistic MRI-constructed subject's head model (2). EEG power spectrum ranging (4-7 Hz), (8-12 Hz) and (13-30 Hz) rhythms was computed for scalp regions modeling roughly the responses of pre-frontal (PF), primary contralateral and ipsilateral sensorimotor (MI), mid-frontal (i.e. supplementary motor area, SMA), and superior posterior parietal (PP) areas. Results and Conclusions. During the visual feed-back period, PF and rhythms were lower and SMA, MIs and PP rhythms were higher for the WM than NOWM (Fig. 1). So higher was SMA rhythm. After the visual feedback, PF, SMA and MIs rhythms were lower for the WM than NOWM. In conclusion, in a distributed cortical frontoparietal system, post-movement updating of visuomotor transformations would occur during the feed-back for the NOWM ("on-line updating") and after the feed-back for the WM ("delayed updating"). PF may play a role in this "delayed updating", possibly matching actively memorized visual instruction and feed-back stimuli.