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Front Behav Neurosci. 2015 May 6;9:111. doi: 10.3389/fnbeh.2015.00111. eCollection 2015.

Pre-stimulus BOLD-network activation modulates EEG spectral activity during working memory retention.

Author information

1
Translational Research Center, University Hospital of Psychiatry and Psychotherapy, University Bern Psychiatric Services (UPS) Bern, Switzerland ; Chronobiology and Sleep Research, Institute of Pharmacology and Toxicology, University of Zurich Zurich, Switzerland ; Center for Cognition, Learning and Memory, University of Bern Bern, Switzerland.
2
Department of Child and Adolescent Psychiatry, University of Zurich Zurich, Switzerland.
3
Translational Research Center, University Hospital of Psychiatry and Psychotherapy, University Bern Psychiatric Services (UPS) Bern, Switzerland ; Center for Cognition, Learning and Memory, University of Bern Bern, Switzerland.
4
Institute of Neuroradiology, University Hospital Zurich Zurich, Switzerland.
5
Department of Child and Adolescent Psychiatry, University of Zurich Zurich, Switzerland ; Department of Child and Adolescent Psychiatry and Psychotherapy, Medical Faculty, Central Institute of Mental Health, Mannheim/Heidelberg University Mannheim, Germany ; Zurich Center for Integrative Human Physiology, University of Zurich Zurich, Switzerland ; Neuroscience Center Zurich, University and ETH Zurich Zurich, Switzerland.

Abstract

Working memory (WM) processes depend on our momentary mental state and therefore exhibit considerable fluctuations. Here, we investigate the interplay of task-preparatory and task-related brain activity as represented by pre-stimulus BOLD-fluctuations and spectral EEG from the retention periods of a visual WM task. Visual WM is used to maintain sensory information in the brain enabling the performance of cognitive operations and is associated with mental health. We tested 22 subjects simultaneously with EEG and fMRI while performing a visuo-verbal Sternberg task with two different loads, allowing for the temporal separation of preparation, encoding, retention and retrieval periods. Four temporally coherent networks (TCNs)-the default mode network (DMN), the dorsal attention, the right and the left WM network-were extracted from the continuous BOLD data by means of a group ICA. Subsequently, the modulatory effect of these networks' pre-stimulus activation upon retention-related EEG activity in the theta, alpha, and beta frequencies was analyzed. The obtained results are informative in the context of state-dependent information processing. We were able to replicate two well-known load-dependent effects: the frontal-midline theta increase during the task and the decrease of pre-stimulus DMN activity. As our main finding, these two measures seem to depend on each other as the significant negative correlations at frontal-midline channels suggested. Thus, suppressed pre-stimulus DMN levels facilitated later task related frontal midline theta increases. In general, based on previous findings that neuronal coupling in different frequency bands may underlie distinct functions in WM retention, our results suggest that processes reflected by spectral oscillations during retention seem not only to be "online" synchronized with activity in different attention-related networks but are also modulated by activity in these networks during preparation intervals.

KEYWORDS:

BOLD-ICA; covariance mapping; frontal-midline theta; pre-stimulus state; state dependency; temporally coherent brain networks; working memory

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