title: Signal Propagation in the Human Visual Pathways: An Effective Connectivity Analysis.
abstract: Although the visual system has been extensively investigated, an integrated account of the spatiotemporal dynamics of long-range signal propagation along the human visual pathways is not completely known or validated. In this work, we used dynamic causal modeling approach to provide insights into the underlying neural circuit dynamics of pattern reversal visual-evoked potentials extracted from concurrent EEG-fMRI data. A recurrent forward-backward connectivity model, consisting of multiple interacting brain regions identified by EEG source localization aided by fMRI spatial priors, best accounted for the data dynamics. Sources were first identified in the thalamic area, primary visual cortex, as well as higher cortical areas along the ventral and dorsal visual processing streams. Consistent with hierarchical early visual processing, the model disclosed and quantified the neural temporal dynamics across the identified activity sources. This signal propagation is dominated by a feedforward process, but we also found weaker effective feedback connectivity. Using effective connectivity analysis, the optimal dynamic causal modeling revealed enhanced connectivity along the dorsal pathway but slightly suppressed connectivity along the ventral pathway. A bias was also found in favor of the right hemisphere consistent with functional attentional asymmetry. This study validates, for the first time, the long-range signal propagation timing in the human visual pathways. A similar modeling approach can potentially be used to understand other cognitive processes and dysfunctions in signal propagation in neurological and neuropsychiatric disorders. Significance statement: An integrated account of long-range visual signal propagation in the human brain is currently incomplete. Using computational neural modeling on our acquired concurrent EEG-fMRI data under a visual evoked task, we found not only a substantial forward propagation toward "higher-order" brain regions but also a weaker backward propagation. Asymmetry in our model's long-range connectivity accounted for the various observed activity biases. Importantly, the model disclosed the timing of signal propagation across these connectivity pathways and validates, for the first time, long-range signal propagation in the human visual system. A similar modeling approach could be used to identify neural pathways for other cognitive processes and their dysfunctions in brain disorders.
authors.affiliation: Intelligent Systems Research Centre, Ulster University, Derry-Londonderry, BT48 7JL, United Kingdom, youssofzadeh-v@email.ulster.ac.uk k.wong-lin@ulster.ac.uk.
authors.forename: Vahab
authors.identifier: http://orcid.org/0000-0002-1892-5525
authors.initials: V
authors.lastname: Youssofzadeh
authors.affiliation: Intelligent Systems Research Centre, Ulster University, Derry-Londonderry, BT48 7JL, United Kingdom.
authors.forename: Girijesh
authors.identifier: http://orcid.org/0000-0003-3284-9589
authors.initials: G
authors.lastname: Prasad
authors.affiliation: National Centre for Advanced Medical Imaging, St. James Hospital/School of Medicine, Trinity College Dublin, Dublin 8, Republic of Ireland, and.
authors.forename: Andrew J
authors.identifier: http://orcid.org/0000-0002-5528-9732
authors.initials: AJ
authors.lastname: Fagan
authors.affiliation: School of Engineering, School of Medicine, Trinity Centre for Bioengineering, Trinity College Dublin, Dublin 2, Republic of Ireland.
authors.forename: Richard B
authors.initials: RB
authors.lastname: Reilly
authors.affiliation: National Centre for Advanced Medical Imaging, St. James Hospital/School of Medicine, Trinity College Dublin, Dublin 8, Republic of Ireland, and.
authors.forename: Sven
authors.initials: S
authors.lastname: Martens
authors.affiliation: National Centre for Advanced Medical Imaging, St. James Hospital/School of Medicine, Trinity College Dublin, Dublin 8, Republic of Ireland, and.
authors.forename: James F
authors.initials: JF
authors.lastname: Meaney
authors.affiliation: Intelligent Systems Research Centre, Ulster University, Derry-Londonderry, BT48 7JL, United Kingdom, youssofzadeh-v@email.ulster.ac.uk k.wong-lin@ulster.ac.uk.
authors.forename: KongFatt
authors.initials: K
authors.lastname: Wong-Lin
mesh_terms: D000328:Adult; D001931:Brain Mapping; D002540:Cerebral Cortex / Q000502:physiology; D004569:Electroencephalography; D005074:Evoked Potentials, Visual; D056228:Feedback, Sensory / Q000502:physiology; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D008959:Models, Neurological; D009434:Neural Pathways / Q000502:physiology*; D013788:Thalamus / Q000502:physiology; D014793:Visual Cortex / Q000502:physiology; D014795:Visual Pathways / Q000502:physiology*; D055815:Young Adult
keywords: concurrent EEG-fMRI; dorsal pathway; dynamic causal modeling; ventral pathway; visual-evoked potentials