title: Simultaneous EEG-fMRI during a working memory task: modulations in low and high frequency bands.
abstract: BACKGROUND
  EEG studies of working memory (WM) have demonstrated load dependent frequency band modulations. FMRI studies have localized load modulated activity to the dorsolateral prefrontal cortex (DLPFC), medial prefrontal cortex (MPFC), and posterior parietal cortex (PPC). Recently, an EEG-fMRI study found that low frequency band (theta and alpha) activity negatively correlated with the BOLD signal during the retention phase of a WM task. However, the coupling of higher (beta and gamma) frequencies with the BOLD signal during WM is unknown.
  
  
  METHODS
  In 16 healthy adult subjects, we first investigated EEG-BOLD signal correlations for theta (5-7 Hz), alpha1 (8-10), alpha2 (10-12 Hz), beta1 (13-20), beta2 (20-30 Hz), and gamma (30-40 Hz) during the retention period of a WM task with set size 2 and 5. Secondly, we investigated whether load sensitive brain regions are characterised by effects that relate frequency bands to BOLD signals effects.
  
  
  RESULTS
  We found negative theta-BOLD signal correlations in the MPFC, PPC, and cingulate cortex (ACC and PCC). For alpha1 positive correlations with the BOLD signal were found in ACC, MPFC, and PCC; negative correlations were observed in DLPFC, PPC, and inferior frontal gyrus (IFG). Negative alpha2-BOLD signal correlations were observed in parieto-occipital regions. Beta1-BOLD signal correlations were positive in ACC and negative in precentral and superior temporal gyrus. Beta2 and gamma showed only positive correlations with BOLD, e.g., in DLPFC, MPFC (gamma) and IFG (beta2/gamma). The load analysis revealed that theta and--with one exception--beta and gamma demonstrated exclusively positive load effects, while alpha1 showed only negative effects.
  
  
  CONCLUSIONS
  We conclude that the directions of EEG-BOLD signal correlations vary across brain regions and EEG frequency bands. In addition, some brain regions show both load sensitive BOLD and frequency band effects. Our data indicate that lower as well as higher frequency brain oscillations are linked to neurovascular processes during WM.
authors.affiliation: Functional Neurosurgery, University Hospital Zürich, Zürich, Switzerland. lars.michels@kispi.uzh.ch
authors.forename: Lars
authors.initials: L
authors.lastname: Michels
authors.forename: Kerstin
authors.initials: K
authors.lastname: Bucher
authors.forename: Rafael
authors.initials: R
authors.lastname: Lüchinger
authors.forename: Peter
authors.initials: P
authors.lastname: Klaver
authors.forename: Ernst
authors.initials: E
authors.lastname: Martin
authors.forename: Daniel
authors.initials: D
authors.lastname: Jeanmonod
authors.forename: Daniel
authors.initials: D
authors.lastname: Brandeis
mesh_terms: D000328:Adult; D000513:Alpha Rhythm; D001611:Beta Rhythm; D001931:Brain Mapping; D004569:Electroencephalography / Q000379:methods*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008570:Memory, Short-Term / Q000502:physiology*; D010100:Oxygen / Q000097:blood; D013826:Theta Rhythm; D055815:Young Adult
chemical_list: D010100:Oxygen