ABSTRACT
We reported the changes of brain responses during sleep following auditory, visual, somatosensory and painful somatosensory stimulation by using magnetoencephalography (MEG). Surprisingly, very large changes were found under all conditions, although the changes in each were not the same. However, there are some common findings. Short-latency components, reflecting the primary cortical activities generated in the primary sensory cortex for each stimulus kind, show no significant change, or are slightly prolonged in latency and decreased in amplitude. These findings indicate that the neuronal activities in the primary sensory cortex are not affected or are only slightly inhibited during sleep. By contrast, middle- and long-latency components, probably reflecting secondary activities, are much affected during sleep. Since the dipole location is changed (auditory stimulation), unchanged (somatosensory stimulation) or vague (visual stimulation) between the state of being awake and asleep, different regions responsible for such changes of activity may be one explanation, although the activated regions are very close to each other. The enhancement of activities probably indicates two possibilities, an increase in the activity of excitatory systems during sleep, or a decrease in the activity of some inhibitory systems, which are active in the awake state. We have no evidence to support either, but we prefer the latter, since it is difficult to consider why neuronal activities would be increased during sleep.
Subject(s)
Auditory Perception/physiology , Magnetoencephalography/methods , Sleep/physiology , Somatosensory Cortex/physiology , Visual Perception/physiology , Adult , Electroencephalography , Evoked Potentials, Auditory/physiology , Evoked Potentials, Somatosensory/physiology , Evoked Potentials, Visual/physiology , Female , Humans , Male , Middle Aged , Neurons/physiology , Perceptual Masking/physiologyABSTRACT
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.
