Structure of visual evoked magnetic field during sleep in humans

To investigate the effects of sleep on the visual evoked magnetic fields (VEF), we recorded VEF following flash light stimulation in healthy adults during sleep. The awake VEF contained several components with approximate latencies of 40, 55, 65, 80, 100, 110, 150, and 180 ms. In contrast, the sleep VEF contained mainly three components with approximate latencies of 65, 100 and 115 ms. By comparing the magnetic components between the awake and sleep conditions based on similarities in the contour pattern of the isomagnetic field, three components for the sleep condition were found to be enhanced, those at 55, 80-100 and 100-110 ms in the awake VEF. Other components of the awake VEF may be reduced or disappear during sleep. This large change in the VEF during sleep suggests that some qualitative changes occur in the cortical visual processing, for example, a reduction in the inhibitory activities at works while awake.