Effects of visual and auditory stimulation on somatosensory evoked magnetic fields

Design and methods: We investigated the effects of continuous visual (cartoon and random dot motion) and auditory (music) stimulation on somatosensory evoked magnetic fields (SEFs) following electrical stimulation of the median nerve on 12 normal subjects using paired t test and two way ANOVA for the statistics. Results: In the hemisphere contralateral to the stimulated nerve, the middle-latency components (35–60 ms in latency) were significantly enhanced by visual, but not by auditory stimulation. The dipoles of all components within 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 ipsilateral hemisphere, the middle-latency components (70–100 ms in latency), the dipoles of which were estimated to be in the second sensory cortex (SII), were markedly decreased in amplitude by both the visual and auditory stimulation. Conclusions: These changes in waveform by visual and auditory stimulation are thought to be due to the effects of the activation of polymodal neurons, which receive not only somatosensory but also visual and/or auditory inputs, in areas 5 and/or 7 as well as in the medial superior temporal region (MST) and superior temporal sulcus (STS), although a change of attention might also be a factor causing such findings.