Neuromagnetic imaging studies discriminate proprioceptive and cutaneous cortical inputs during median nerve stimulation in man

The localizing capabilities of the neuromagnetic imaging technique have been used to non-invasively discriminate mainly proprioceptive from cutaneous afferences to the contralateral hemisphere in human volunteers during separate median nerve stimulation at wrist and digits. The high time-resolution achieved in the localization of the equivalent sources of the early latency (15-30 ms) evoked fields permitted to follow their apparent movement as represented by an early and deep dipole (15 ms, about 5 cm deep, probably a subcortical source), a shallower one (20 ms, about 1.5 cm), and an intermediate one (23 ms, about 3 cm). These sources are supposed to be the manifestation of time-lagged parallel proprioceptive and cutaneous afferences from the thalamic ventro basal complex to different primary sensory areas in the postcentral gyrus. Both deeper and shallower dipoles could not be identified during selective stimulation of cutaneous afferents from the digital branches of the median nerve.