title: Cortical subnetwork dynamics during human language tasks.
abstract: Language tasks require the coordinated activation of multiple subnetworks-groups of related cortical interactions involved in specific components of task processing. Although electrocorticography (ECoG) has sufficient temporal and spatial resolution to capture the dynamics of event-related interactions between cortical sites, it is difficult to decompose these complex spatiotemporal patterns into functionally discrete subnetworks without explicit knowledge of each subnetwork's timing. We hypothesized that subnetworks corresponding to distinct components of task-related processing could be identified as groups of interactions with co-varying strengths. In this study, five subjects implanted with ECoG grids over language areas performed word repetition and picture naming. We estimated the interaction strength between each pair of electrodes during each task using a time-varying dynamic Bayesian network (tvDBN) model constructed from the power of high gamma (70-110Hz) activity, a surrogate for population firing rates. We then reduced the dimensionality of this model using principal component analysis (PCA) to identify groups of interactions with co-varying strengths, which we term functional network components (FNCs). This data-driven technique estimates both the weight of each interaction's contribution to a particular subnetwork, and the temporal profile of each subnetwork's activation during the task. We found FNCs with temporal and anatomical features consistent with articulatory preparation in both tasks, and with auditory and visual processing in the word repetition and picture naming tasks, respectively. These FNCs were highly consistent between subjects with similar electrode placement, and were robust enough to be characterized in single trials. Furthermore, the interaction patterns uncovered by FNC analysis correlated well with recent literature suggesting important functional-anatomical distinctions between processing external and self-produced speech. Our results demonstrate that subnetwork decomposition of event-related cortical interactions is a powerful paradigm for interpreting the rich dynamics of large-scale, distributed cortical networks during human cognitive tasks.
authors.affiliation: Department of Neurology, Johns Hopkins University, 600 N. Wolfe St., Meyer 2-161, Baltimore, MD 21287, USA; Department of Biomedical Engineering, Johns Hopkins University, 720 Rutland Ave., Baltimore, MD 21205, USA. Electronic address: collard@jhu.edu.
authors.forename: Maxwell J
authors.initials: MJ
authors.lastname: Collard
authors.affiliation: Department of Biomedical Engineering, Johns Hopkins University, 720 Rutland Ave., Baltimore, MD 21205, USA.
authors.forename: Matthew S
authors.initials: MS
authors.lastname: Fifer
authors.affiliation: Department of Biomedical Engineering, Johns Hopkins University, 720 Rutland Ave., Baltimore, MD 21205, USA; Center for Devices and Radiological Health, U.S. Food and Drug Administration, 10903 New Hampshire Ave., Silver Spring, MD 20993, USA.
authors.forename: Heather L
authors.initials: HL
authors.lastname: Benz
authors.affiliation: Department of Neurosurgery, Johns Hopkins University, 600 N. Wolfe St., Baltimore, MD 21287, USA.
authors.forename: David P
authors.initials: DP
authors.lastname: McMullen
authors.affiliation: Department of Biomedical Engineering, Johns Hopkins University, 720 Rutland Ave., Baltimore, MD 21205, USA; Fischell Department of Bioengineering, University of Maryland, Room 2330 Jeong H. Kim Engineering Building (Bldg. # 225), College Park, MD 20742, USA.
authors.forename: Yujing
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Department of Biomedical Engineering, Johns Hopkins University, 720 Rutland Ave., Baltimore, MD 21205, USA.
authors.forename: Griffin W
authors.initials: GW
authors.lastname: Milsap
authors.affiliation: Department of Neurology, Johns Hopkins University, 600 N. Wolfe St., Meyer 2-161, Baltimore, MD 21287, USA.
authors.forename: Anna
authors.initials: A
authors.lastname: Korzeniewska
authors.affiliation: Department of Neurology, Johns Hopkins University, 600 N. Wolfe St., Meyer 2-161, Baltimore, MD 21287, USA.
authors.forename: Nathan E
authors.initials: NE
authors.lastname: Crone
mesh_terms: D001931:Brain Mapping / Q000379:methods*; D002540:Cerebral Cortex / Q000502:physiology*; D003198:Computer Simulation; D000069280:Electrocorticography / Q000379:methods*; D005260:Female; D006801:Humans; D007802:Language; D008297:Male; D008959:Models, Neurological; D009415:Nerve Net / Q000502:physiology*; D011932:Reading; D013060:Speech / Q000502:physiology; D055815:Young Adult
keywords: Electrocorticography (ECoG); Functional connectivity; High gamma; Language networks; Speech processing; Subnetworks