Somatosensory evoked magnetic fields to median nerve stimulation in newborns

We studied somatosensory evoked magnetic fields (SEFs) to electric and tactile stimulation in newborns. The electric stimulation was applied to the left median nerve at the wrist and the tactile stimulation to the tip of the left or right index finger. An interstimulus interval of 2 s was used. The evoked magnetic fields were measured over the right hemisphere with a 306-channel MEG-system (Elekta Neuromag Oy). The data were off-line analyzed for active and quiet sleep stages. The first deflection after the median nerve stimulation, M30, corresponding to the adult N20 m, peaked at about 30 ms. The field pattern of this early peak was dipolar, and the activity could be modeled using an equivalent current dipole (ECD). The coordinates of the ECD were in agreement with activity generated at the primary somatosensory cortex, the current dipole pointing anteriorly. The locations of the later deflections were compared with the origin of M30.