The role of alpha and theta oscillations in a working memory task with anticipated distractors

Working memory (WM) can be defined as the brain ability to store information for a brief period of time, for manipulation and retrieval. Since working memory has a limited capacity, it is fundamental to direct neural resources towards the processing of task-relevant information and to ignore the task-irrelevant ones. Recent studies have highlighted the role of theta (4-8 Hz) and alpha (8-13 Hz) oscillations in WM tasks, with the first being mainly implicated in encoding of relevant information and the second in inhibiting interfering information. The aim of this thesis project is to investigate brain alpha and theta rhythms in a Sternberg visual working memory task (encoding of 5 typed letters) with anticipated distractor, i.e. distractor presented during the retention phase always with the same timing within each trial and always of the same type, trial by trial, so that the subject is able to predict its onset and nature in each trial. 64-channels EEG data were acquired in 21 young healthy subjects while performing the visual WM task with anticipated distractors. We compared the conditions of two distractors of different interfering strength (typed letters vs typed symbols) and the conditions of two distractors of different sensory modality (typed letters vs pronounced letters). EEG data were analyzed at the scalp and cortical level (after solution of the inverse problem), focusing on theta activity during the encoding phase and on alpha activity during the retention phase (immediately before distractor presentation). Results highlight a general alpha increase during the retention phase, but with differences in some specific cortical regions, depending on the contrasted conditions, supporting an inhibitory role of alpha rhythm, and a general theta increase during the encoding phase, stronger in case of typed letters. Results are discussed and commented with respect to existing data in literature.