title: Effects of verbal working memory load on corticocortical connectivity modeled by path analysis of functional magnetic resonance imaging data.
abstract: We investigated the hypothesis that there are load-related changes in the integrated function of frontoparietal working memory networks. Functional magnetic resonance imaging time-series data from 10 healthy volunteers performing a graded n-back verbal working memory task were modeled using path analysis. Seven generically activated regions were included in the model: left/right middle frontal gyri (L/R MFG), left/right inferior frontal gyri (L/R IFG), left/right posterior parietal cortex (L/R PPC), and supplementary motor area (SMA). The model provided a good fit to the 1-back (chi(2) = 7.04, df = 8, P = 0.53) and 2-back conditions (chi(2) = 9.35, df = 8, P = 0.31) but not for the 3-back condition (chi(2) = 20.60, df = 8, P = 0.008). Model parameter estimates were compared overall among conditions: there was a significant difference overall between 1-back and 2-back conditions (chi(2)(diff) = 74.77, df = 20, P < 0.001) and also between 2-back and 3-back conditions (chi(2)(diff) = 96.28, df = 20, P < 0.001). Path coefficients between LIFG and LPPC were significantly different from zero in both 1-back and 2-back conditions; in the 2-back condition, additional paths from LIFG to LPPC via SMA and to RMFG from LMFG and LPPC were also nonzero. This study demonstrated a significant change in functional integration of a neurocognitive network for working memory as a correlate of increased load. Enhanced inferior frontoparietal and prefrontoprefrontal connectivity was observed as a correlate of increasing memory load, which may reflect greater demand for maintenance and executive processes, respectively.
authors.affiliation: Department of Psychiatry, University of Cambridge, Cambridge CB2 2QQ, United Kingdom.
authors.forename: G D
authors.initials: GD
authors.lastname: Honey
authors.forename: C H Y
authors.initials: CH
authors.lastname: Fu
authors.forename: J
authors.initials: J
authors.lastname: Kim
authors.forename: M J
authors.initials: MJ
authors.lastname: Brammer
authors.forename: T J
authors.initials: TJ
authors.lastname: Croudace
authors.forename: J
authors.initials: J
authors.lastname: Suckling
authors.forename: E M
authors.initials: EM
authors.lastname: Pich
authors.forename: S C R
authors.initials: SC
authors.lastname: Williams
authors.forename: E T
authors.initials: ET
authors.lastname: Bullmore
mesh_terms: D000328:Adult; D001931:Brain Mapping; D002540:Cerebral Cortex / Q000033:anatomy & histology / Q000502:physiology*; D005260:Female; D005625:Frontal Lobe / Q000502:physiology; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008570:Memory, Short-Term / Q000502:physiology*; D008959:Models, Neurological; D009415:Nerve Net / Q000502:physiology; D009434:Neural Pathways / Q000033:anatomy & histology / Q000502:physiology; D010296:Parietal Lobe / Q000502:physiology; D014706:Verbal Learning / Q000502:physiology*