Spatial extent of coherent sensory-evoked cortical activity

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.