Amplitude spectrum EEG signal evidence for the dissociation of motor and perceptual spatial working memory in the human brain

Abstract

This study investigated the question whether spatial working memory related to movement plans (motor working memory) and spatial working memory related to spatial attention and perceptual processes (perceptual spatial working memory) share the same neurophysiological substrate or there is evidence for separate motor and perceptual working memory streams of processing. Towards this aim, ten healthy human subjects performed delayed responses to visual targets presented at different spatial locations. Two tasks were attained, one in which the spatial location of the target was the goal for a pointing movement and one in which the spatial location of the target was used for a perceptual (yes or no) change detection. Each task involved two conditions: a memory condition in which the target remained visible only for the first 250 ms of the delay period and a delay condition in which the target location remained visible throughout the delay period. The amplitude spectrum analysis of the EEG revealed that the alpha (8-12 Hz) band signal was smaller, while the beta (13-30 Hz) and gamma (30-45 Hz) band signals were larger in the memory compared to the non-memory condition. The alpha band signal difference was confined to the frontal midline area; the beta band signal difference extended over the right hemisphere and midline central area, and the gamma band signal difference was confined to the right occipitoparietal area. Importantly, both in beta and gamma bands, we observed a significant increase in the movement-related compared to the perceptual-related memory-specific amplitude spectrum signal in the central midline area. This result provides clear evidence for the dissociation of motor and perceptual spatial working memory.

Granger causality analysis reveals distinct spatio-temporal connectivity patterns in motor and perceptual visuo-spatial working memory

“…A total of 2880 trials were recorded, but we rejected 761 of them based on behavioral and electrophysiological criteria. 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 (movement task) 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 (change detection task). Using these criteria, 259 trials (9%, range for all subjects: 2.5–20%) were removed.…”

“…This study addressed the question whether there are separate spatial WM processing streams in the brain for movement vs. spatial perception using two memory tasks. In our previous study using the same data set (Smyrnis et al, 2014 ) we examined the behavioral performance of these two memory tasks and showed that the memorization of the target location in the movement and the change detection tasks did not have any different effect on reaction time or loss of spatial accuracy, thus favoring the hypothesis of a common mechanism of spatial WM as these tasks are concerned. Amplitude spectrum analysis of the EEG, in that same study (Smyrnis et al, 2014 ) revealed that the α (8–12 Hz) band signal was smaller while the β (13–30 Hz) and γ (30–45 Hz) band signals were larger in the memory compared to the non-memory condition.…”

“…Four types of trials were performed by ten right-handed volunteers (seven men and three women) between the ages of 29 and 44 (mean age of 35) in a randomized order as described in a previous study (Smyrnis et al, 2014 ). All participants had no history of major medical or psychiatric illness and had normal or corrected-to-normal vision.…”

“…However, up to date, the question whether there are separate spatial WM processing streams in the brain for movement vs. spatial perception has not been resolved. In a recent study (Smyrnis et al, 2014 ) we tried to address this issue using scalp electroencephalographic recordings (EEG). The experiment involved memory and non-memory conditions on two tasks: one in which the spatial location of the target served as a goal for a 2D pointing movement (movement task) and one in which the spatial location of the target served as the onset of a perceptual yes/no decision (change detection task).…”

Oscillatory brain activity and maintenance of verbal and visual working memory: a systematic review

“…Two of them yielded null findings (Rawle et al, 2012;Zhang et al, 2016). Gamma decreased in two other studies (Pahor and Jausovec, 2017;Smyrnis et al, 2014). In one study gamma quickly disappeared after initial (~800 ms) increase (Tallon-Baudry et al, 1999).…”