A multichannel whole-head EEG study on visual working memory processing of spatiality in the human brain

We aimed to study the processing of spatiality in the human brain using a 64-channel whole-head EEG system and simply structured 1-back comparison memory tasks with visuospatial patterns. 8 healthy human subjects participated in this study. The memory tasks with different spatial loads consisted in the presentation of 1, 2 or 3 small white squares on a black background every 4 seconds for a period of 500ms each (1 degree of visual angle per square), in 6 different positions inside the lower 2/3rd of the central visual field. The subjects were instructed to fixate a small cross in the center of the computer monitor and perform the tasks in 1-back fashion (80% different — 20% same, responding to same stimuli). In another control condition subjects were presented with the same set of patterns, except that they were instructed to perform the tasks in a simple visuomotor reaction fashion (response hands were counterbalanced across subjects). Data were analyzed in the time domain (after appropriate preprocessing, artifact elimination with ICA and averaging to ERPs, statistics on scalp data, distributed current source modeling performed with LORETA solution) and time-frequency domain (comparison and statistics on original scalp event-related power changes in different frequency bands). The results of this study showed the involvement of parietal cortices in the acquisition of spatiality, left anterior temporal cortices in the short-term memory encoding processes and the right prefrontal cortical areas in visuospatial attentional, short-term encoding and maintenance processes. Time courses of the estimated source activities and their possible interaction during these processes were also evaluated. In time-frequency space, the most significant results related to the memory processing of spatiality were considered the signal power decrease in the parietofrontal sites and increase in the centrotemporal sites (compared to the prestimulus baseline activity).