Magnetoencephalographic investigations of cortical reorganization in humans.

The central representation of sensory perception relates in an orderly way to the spatial arrangement of receptors in the periphery. The cortical maps of visual space (retinotopy), the body surface (somatotopy), or tone frequency (cochlear place; tontotopy) can be individually determined by means of magnetic source imaging. In a similar manner, it is possible to map motor organization along the central sulcus. Usually, a first major peak of the magnetic field evoked by a sensory stimulus is determined and a single equivalent moving dipole is fitted to the field measured from sensors over the respective primary cortical area. Tactile evoked fields, for instance, show a first major peak around 30-70 ms after stimulus onset. The field pattern of short-latency somatosensory components is fairly dipolar and a single moving dipole is an adequate model to localize the generator of this SEF component in most cases. This generator is located in area 3b contralateral to the stimulated site [1-5].