Evolution of neuromagnetic topographic mapping.

Magnetoencephalography has developed during the past twenty years with a different overall emphasis than found in electroencephalography. These differences are explored in selected applications. One dominant feature of magnetic studies is a quantitative approach to characterize the strength of neuronal activity, as well as its position within the brain. There is evidence from recent analyses of current source-density measurements in animal models that the deduced peak neuronal strength can also be interpreted in terms of the spatial extent of activity across cortex.