Middle and long latency peak sources in auditory evoked magnetic fields for tone bursts in humans

The relative position of the P50m and the N100m sources of the auditory evo ked magnetic field remains unclear. Magnetoencephalography was performed in 24 normal subjects. Contralateral P50m to left and right ear stimulus was observed in 21 and 19 hemispheres, respectively. Ipsilateral P50m to left a nd right ear stimulus was observed in 17 and 16 hemispheres, respectively. N100m was observed in all subjects for all stimuli. Relative position of th e equivalent current dipole of the P50m was 1.0 +/- 7.6 (mean +/- SD) mm po sterior, 2.0 +/- 5.8 mm inferior and 1.8 +/- 8.0 mm medial to the N100m dip ole position considering all observations. We suggest that the P50m and N10 0m sources are colocated in an extended area of the cortex. (C) 2000 Elsevi er Science Ireland Ltd. All rights reserved.