Effects of visual and auditory stimulation on somatosensory evoked magnetic fields

Design and methods: We investigated the effects of continuous visual (carto on and random dot motion) and auditory (music) stimulation on somatosensory evoked magnetic fields (SEFs) following electrical stimulation of the medi an nerve on 12 normal subjects using paired t test and two way ANOVA for th e statistics. Results: In the hemisphere contralateral to the stimulated nerve, the middl e-latency components (35-60 ms in latency) were significantly enhanced by v isual, but not by auditory stimulation. The dipoles of all components withi n 60-70 ms following stimulation were estimated to be very close each other , around the hand area of the primary sensory cortex (SI). In the ipsilater al hemisphere, the middle-latency components (70-100 ms in latency), the di poles of which were estimated to be in the second sensory cortex (SII), wer e markedly decreased in amplitude by both the visual and auditory stimulati on. Conclusions: These changes in waveform by visual and auditory stimulation a re thought to be due to the effects of the activation of polymodal neurons, which receive not only somatosensory but also visual and/or auditory input s, in areas 5 and/or 7 as well as in the medial superior temporal region (M ST) and superior temporal sulcus (STS), although a change of attention migh t also be a factor causing such findings. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.