Spatial extent of coherent sensory-evoked cortical activity

Abstract

Analysis of published values for the depth profile of evoked potentials in primary sensory cortex of cat and monkey provide a consistent estimate for the net current dipole moment per unit area of cortical surface. Comparison with values of the total current dipole moment obtained from neuromagnetic studies on human subjects indicates that coherent neuronal activity giving rise to long-latency sensory evoked components recorded in the human electroencephalogram or magnetoencephalogram extends over a cortical area that is typically approximately 40-400 mm2.

Invariance in current dipole moment density across brain structures and species: Physiological constraint for neuroimaging

“…These values matched the value of q primary previously computed for the monkey visual cortex by Lü and Williamson (1991). We then estimated q primary in the neocortex of rat and human based on previous MEG studies by others.…”

“…The q primary estimated by Lü and Williamson (1991) for the data reported by Mitzdorf and Singer (1979) was 0.39–0.40 nAm/mm 2 for the monkey in a condition where the population activity was evoked by an electrical stimulation of the optic chiasm. Lü and Williamson (1991) also estimated q primary for visually evoked responses in the visual cortex of cat. In this case the maximum value was 0.14 nAm/mm 2 , lower than the electrically evoked responses.…”

“…It is 0.40 nAm/mm 2 in monkey visual cortex (Lü and Williamson, 1991). The estimate is based on the CSD analysis of the evoked responses in Area 17 of the monkey produced by electrical stimulation of the optic chiasm (Mitzdorf and Singer, 1979), not on MEG data.…”

“…turtle cerebellum - Okada and Nicholson, 1988; Okada et al, 1989; guinea pig hippocampus - Murakami et al, 2002, 2003; swine neocortex - Okada et al, 1996; and monkey visual cortex - Lü and Williamson, 1991). The straightforward method of estimating q according to this definition is problematic because it does not necessarily estimate the q primary strictly due to neuronal currents.…”

Modeling the effect of dendritic input location on MEG and EEG source dipoles

“…In particular, excitatory inputs to the apical tuft of pyramidal cells in the superficial cortical layers result in surface negative EEG [14,66], corresponding to current dipole direction towards the white matter. Multi-contact intracranial recordings can provide data about the expected dipole direction in terms of laminar input patterns and neural excitation [8,20,40,44,52,58]. For the interpretation of the macroscopic current dipole in terms of the input type, however, it will be important to relate the laminar locations of the synaptic inputs to their locations within the dendritic tree of the individual neurons [50].…”