Although the information from the visual hemifield is largely represented in the contralateral brain, there is also representation of visual hemifield in the ipsilateral brain. Similarly, it has been shown that visual motion in the hemifield is also represented in the ipsilateral extrastriate area. However, the characteristics of such representation have not been fully demonstrated. In the present study, we recorded the neuromagnetic response to apparent motion visual stimuli in one hemifield from both cerebral hemispheres using magnetoencephalography, and examined the characteristics of signal transmission to bilateral MT+ areas. Three normal adults were used. The apparent motion visual stimuli, consisted of two vertical bars, were presented with varied eccentricities of 0.5-3.5 degree visual angle. The neuromagnetic responses, generated around MT+ area, were studied. When the stimulus was presented within the foveal field, the latency of the ipsilateral response (mean±SD: 158.7±4.1ms) was almost the same with contralateral one (151.9±6.9ms), suggesting direct input via the ipsilateral primary visual area. On the other hand, when the stimulus was outside the foveal field, the latency of the ipsilateral response (187.3±6.5ms) was longer by 27±2.9ms than contralateral one (160.2±5.4ms), suggesting indirect input via corpus callosum. The amplitude of the response in both cerebral hemispheres was reduced according to the increase of stimulus eccentricity, and the ipsilateral response was reduced steeply compared to contralateral one. Thus, magnetoencephalography could demonstrate the characteristics of signal transmission to bilateral MT+areas.
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