閃光刺激下における脳幹網様体興奮性に及ぼす外来刺激の影響(1)

Abstract

The changes in excitability of the brainstem reticular formation due to exteroceptive stimulation in the presence and absence of flash stimuli was studied in the rabbit. The exteroceptive stimulation consisted of the attachment of a soft or hard contact lens (CL) to the eye of the rabbit.1) The threshold of the arousal reaction appearing in the cerebral cortex EEG and the hippocampal EEG elicited by stimulation of the midbrain reticular formation with 100 Hz increases on attachment of the soft CL and the hard CL in the absence of flash stimulus but decreases in the presence of the flash stimulus. The rate of change in the arousal reaction threshold is higher with the hard CL than with the soft CL.2) The threshold of the evoked muscular discharge a ppearing in the fore- and hind limbs by 100 Hz stimulation of the midbrain reticular formation increases in most cases on attachment of the soft CL and the hard CL in the absence of flash stimulus but showed little change or decreased in the psesence of the flash stimulus.These findings suggest that excitabilit y of the brainstem reticular formation is suppressed by attachment of the contact lens in the absence of flash stimulus and the level of activity of consciousness and motor function declines whereas excitability of the brainstem reticular formation is intensified and the level of activity of consciousness and motor function tends to rise by attachment of the CL when flash stimulus is present. It is believed that the diffuse thalamocortical projection system and the limbic system are involved in this mechanism.