[Electroencephalographic changes during experimental plateau waves].

The present study was designed to induce plateau waves by electrical stimulation of the brain stem and examine the changes in EEG during the plateau waves. Experiments were carried out on 10 adult mongrel dogs which were slightly anesthetized, immobilized and artificially respired. Electroencephalogram (EEG), intracranial pressure (ICP), systemic blood pressure (SBP) and cerebral perfusion pressure were simultaneously recorded on the electromagnetic tape after transorbital puncture of the intracavernous internal carotid artery. EEGs were recorded from cortical electrodes, and were analyzed by a frequency analysis. At the stage of increased ICP, the mesencephalic reticular formation was stimulated. Stimulation parameters, i.e., intensity, duration and frequency, were 0.1 mA, 1 msec and 40 - 50 Hz, respectively. The total duration of each period was 5 seconds. Spontaneous plateau waves occurred in 2 dogs associated with subarachnoid hemorrhage, subdural hematoma and intraventricular hemorrhage. Plateau waves were induced by electrical stimulation in the mesencephalic reticular formation in one of two dogs with spontaneous plateau waves. Twenty-one repetitions of electrical stimulation induced ten plateau waves. Two plateau waves were induced during slow EEG associated with desynchronization of EEG. Eight plateau waves were induced during fast EEG activity with no changes in EEG before and after the stimulation. In addition, plateau waves occurred immediately after short duration (5 seconds) of electrical stimulation. It seems that CBV increases during plateau waves are due to rapidly occurring neurogenic vasodilatation of cerebral vessels, later augmented by increases in cerebral metabolism. In conclusion, plateau waves are produced in a rigid condition within the cranial cavity by stimulation of the brainstem reticular formation which influences cortical activation and cerebral vasodilatation.