title: Eigenmodes of brain activity: Neural field theory predictions and comparison with experiment.
abstract: Neural field theory of the corticothalamic system is applied to predict and analyze the activity eigenmodes of the bihemispheric brain, focusing particularly on their spatial structure. The eigenmodes of a single brain hemisphere are found to be close analogs of spherical harmonics, which are the natural modes of the sphere. Instead of multiple eigenvalues being equal, as in the spherical case, cortical folding splits them to have distinct values. Inclusion of interhemispheric connections between homologous regions via the corpus callosum leads to further splitting that depends on symmetry or antisymmetry of activity between brain hemispheres, and the strength and sign of the interhemispheric connections. Symmetry properties of the lowest observed eigenmodes strongly constrain the interhemispheric connectivity strengths and unihemispheric mode spectra, and it is predicted that most spontaneous brain activity will be symmetric between hemispheres, consistent with observations. Comparison with the eigenmodes of an experimental anatomical connectivity matrix confirms these results, permits the relative strengths of intrahemispheric and interhemispheric connectivities to be approximately inferred from their eigenvalues, and lays the foundation for further experimental tests. The results are consistent with brain activity being in corticothalamic eigenmodes, rather than discrete "networks" and open the way to new approaches to brain analysis.
authors.affiliation: School of Physics, University of Sydney, New South Wales 2006, Australia; Center for Integrative Brain Function, University of Sydney, New South Wales 2006, Australia. Electronic address: robinson@physics.usyd.edu.au.
authors.forename: P A
authors.initials: PA
authors.lastname: Robinson
authors.affiliation: School of Physics, University of Sydney, New South Wales 2006, Australia; Center for Integrative Brain Function, University of Sydney, New South Wales 2006, Australia.
authors.forename: X
authors.initials: X
authors.lastname: Zhao
authors.affiliation: School of Physics, University of Sydney, New South Wales 2006, Australia; Center for Integrative Brain Function, University of Sydney, New South Wales 2006, Australia; Sir Peter Mansfield Imaging Center, University of Nottingham, Nottingham NG7 2RD, UK, EU.
authors.forename: K M
authors.initials: KM
authors.lastname: Aquino
authors.affiliation: School of Physics, University of Sydney, New South Wales 2006, Australia; Center for Integrative Brain Function, University of Sydney, New South Wales 2006, Australia; Rotman Research Institute at Baycrest, 3560 Bathurst St, Toronto, Ontario, M6A 2E1, Canada.
authors.forename: J D
authors.initials: JD
authors.lastname: Griffiths
authors.affiliation: Center for Integrative Brain Function, University of Sydney, New South Wales 2006, Australia; Design Lab, School of Architecture, Design, and Planning, University of Sydney, New South Wales 2006, Australia.
authors.forename: S
authors.initials: S
authors.lastname: Sarkar
authors.affiliation: School of Physics, University of Sydney, New South Wales 2006, Australia; Center for Integrative Brain Function, University of Sydney, New South Wales 2006, Australia.
authors.forename: Grishma
authors.initials: G
authors.lastname: Mehta-Pandejee
mesh_terms: D001921:Brain / Q000502:physiology*; D063132:Connectome / Q000379:methods*; D006801:Humans; D008959:Models, Neurological; D015233:Models, Statistical