Analysis of EEG alpha oscillations in a visuospatial attention task

Visuospatial attention can be defined as the process that allows humans to prioritize stimuli information coming from a specific area within the visual field, and neglecting stimuli information coming from neighborhood areas. Several studies have suggested alpha rhythm (8-12 Hz) as implicated in attentional prioritization, by acting as an inhibitory mechanism that protects the visual processing against distracter information from unattended spatial locations. The aim of this thesis project is to investigate brain alpha oscillations in a visuospatial attention task, organized in trials: in each trial, a cue (arrow) was presented indicating the hemifield to attend, followed after 2 seconds by probe stimuli requiring a response only in case of a target stimulus appeared in the attended hemifield. EEG (64-channels) was acquired in 13 young healthy participants while performing the task. The analysis was focused on the anticipatory phase of attention shift (between the cue presentation and the probe stimuli presentation), contrasting the conditions attend-left and attend-right to investigate alpha activity modulation depending on the attended direction. EEG data were analyzed at the scalp and cortical level (sLORETA). Results showed lateralized alpha activity increase in the hemisphere ipsilateral to the attended direction, especially in posterior and temporal regions. Moreover, a connectivity analysis combined with indices derived from the graph theory analysis (in-degree and out-degree) highlighted lateralized top-down and bottom-up interactions between the frontal and occipital areas. Results support an inhibitory role of alpha-rhythm over the cortical regions devoted to processing visual input from the unattended hemifield to protect from distracting information. Results are discussed and commented with respect to existing data in literature.