title: The electrophysiological correlates of the working memory subcomponents: evidence from high-density EEG and coherence analysis.
abstract: Synchronization between prefrontal (executive) and posterior (association) cortices seems a plausible mechanism for temporary maintenance of information. However, while EEG studies reported involvement of (pre)frontal midline structures in synchronization, functional neuroimaging elucidated the importance of lateral prefrontal cortex (PFC) in working memory (WM). Verbal and spatial WM rely on lateralized subsystems (phonological loop and visuospatial sketchpad, respectively), yet only trends for hemispheric dissociation of networks supporting rehearsal of verbal and spatial information were identified by EEG. As oscillatory activity is WM load dependent, we applied an individually tailored submaximal load for verbal (V) and spatial (S) task to enhance synchronization in the relevant functional networks. To map these networks, we used high-density EEG and coherence analysis. Our results imply that the synchronized activity is limited to highly specialized areas that correspond well with the areas identified by functional neuroimaging. In both V and S task, two independent networks of theta synchronization involving dorsolateral PFC of each hemisphere were revealed. In V task, left prefrontal and left parietal areas were functionally coupled in gamma frequencies. Theta synchronization thus provides the necessary interface for storage and manipulation of information, while left-lateralized gamma synchronization could represent the EEG correlate of the phonological loop.
authors.affiliation: Institute of Clinical Neurophysiology, University Medical Centre Ljubljana, Zaloška cesta 7, SI-1525, Ljubljana, Slovenia. veronika.rutar@gmail.com.
authors.forename: Veronika
authors.initials: V
authors.lastname: Rutar Gorišek
authors.affiliation: Faculty of Electrical Engineering, University of Ljubljana, Ljubljana, Slovenia. ales.belic@fe.uni-lj.si.
authors.forename: Aleš
authors.initials: A
authors.lastname: Belič
authors.affiliation: Department of Philology, University of Patras, 2654, Rio Patras, Greece. christina.manouilidou@gmail.com.
authors.forename: Christina
authors.initials: C
authors.lastname: Manouilidou
authors.affiliation: Institute of Clinical Neurophysiology, University Medical Centre Ljubljana, Zaloška cesta 7, SI-1525, Ljubljana, Slovenia. blaz.koritnik@kclj.si.
authors.forename: Blaž
authors.initials: B
authors.lastname: Koritnik
authors.affiliation: Department of Psychology, Faculty of Arts, University of Ljubljana, Aškerčeva 2, 1000, Ljubljana, Slovenia. grega.repovs@psy.ff.uni-lj.si.
authors.forename: Grega
authors.initials: G
authors.lastname: Repovš
authors.affiliation: Department of Neurology, University Medical Centre Ljubljana, Zaloška cesta 2, 1000, Ljubljana, Slovenia. jure.bon@gmail.com.
authors.forename: Jure
authors.initials: J
authors.lastname: Bon
authors.affiliation: Faculty of Health Sciences, University of Ljubljana, Zdravstvena pot 4, 1000, Ljubljana, Slovenia. janez.zibert@zf.uni-lj.si.
authors.forename: Janez
authors.initials: J
authors.lastname: Žibert
authors.affiliation: Institute of Clinical Neurophysiology, University Medical Centre Ljubljana, Zaloška cesta 7, SI-1525, Ljubljana, Slovenia. janez.zidar@kclj.si.
authors.forename: Janez
authors.initials: J
authors.lastname: Zidar
mesh_terms: D000328:Adult; D001931:Brain Mapping; D002540:Cerebral Cortex / Q000502:physiology*; D003344:Cortical Synchronization / Q000502:physiology*; D004569:Electroencephalography / Q000379:methods; D055724:Electrophysiological Phenomena / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008570:Memory, Short-Term / Q000502:physiology*; D009483:Neuropsychological Tests; D011930:Reaction Time; D013826:Theta Rhythm / Q000502:physiology*
keywords: Dorsolateral prefrontal cortex; Electroencephalographic coherence; Episodic buffer; Executive function; Theta synchronization; Working memory