Connectivity Analysis Based on Multielectrode EEG Inversion Methods with and without fMRI A Priori Information
Human neocortical processes involve temporal and spatial scales spanning several orders of magnitude, from the rapidly shifting somatosensory processes, characterized by a temporal scale ofmilliseconds and spatial scales of a few squaremillimeters, to the memory processes, involving time periods of seconds and spatial scales of square centimeters. Information about brain activity can be obtained by measuring different physical variables arising from the brain processes, such as the increase in consumption of oxygen by the neural tissues or the variation of the electric potential on the scalp surface. All these variables are connected directly or indirectly to
the neural ongoing processes, and each variable has its own spatial and temporal resolution. The different neuroimaging techniques are then confined to the spatiotemporal resolution offered by the monitored variables. For instance, it is known from physiology that the temporal resolution of the hemodynamic deoxyhemoglobin increase/decrease lies in the range of 1-2 s, while its spatial resolution is generally observable with the current imaging techniques over the scale of a few millimeters.