Neural Field Dynamics on the Folded Three-Dimensional Cortical Sheet and Its Forward EEG and MEG

Abstract

Dynamic systems defined on the scale of neural ensembles are well-suited to model the spatiotemporal dynamics of electroencephalographic (EEG) and magnetoencephalographic (MEG) data. We develop a methodological framework, which defines the activity of neural ensembles, the neural field, on a sphere in three dimensions. Using Magnetic Resonance Imaging (MRI) we map the neural field dynamics from the sphere onto the folded cortical surface of a hemisphere. The neural field represents the current flow perpendicular to the cortex and thus allows the calculation of the electric potentials on the surface of the skull and the magnetic fields outside the skull to be measured by EEG and MEG, respectively. For demonstration of the dynamics, we present the propagation of activation at a single cortical site resulting from a transient input. Non-trivial mappings between the multiple levels of observation are obtained which would not be predicted by inverse solution techniques. Considering recent results mapping large-scale brain dynamics (EEG, MEG) onto behavioral motor patterns, this paper provides a discussion of the causal chain starting from local neural ensemble dynamics through encephalographic data to behavior.