A study of centrally evoked potentials and of effects of lesions on sleep and wakefulness

Abstract

Some areas of midbrain and pons were stimulated with single pulses and the differences in strengths required to cause an arousal response in the electrographic pattern and behavior were studied in free-moving cats having permanently implanted electrodes. Stimulation of the area lateral to nucleus tr. spinalis n. trigemini in lateral pons caused arousal effects even for a single pulse of 0.5 V and 0.3 msec duration. In contrast, the rostral peri-aqueductal grey matter required 13 times, mesencephalic substantia grisea centralis 10-13 times, nucleus reticularis pontis oralis and medial vestibular nuclei 3 times stronger stimuli to evoke similar arousal response. It is discussed that these regional differences lend support to the concept that the brainstem is regionally differentiated and that all of the regions may not be connected with the regulation of wakefulness. Regional specificity was also observed in the forms of potentials evoked in the lateral gyrus by stimuli of lesser magnitude during wakeful state, slow wave phase of sleep and paradoxical phase of sleep. The potentials during slow wave phase of sleep were generally different either in duration or amplitude or wave composition, from those of wakeful state and paradoxical phase of sleep. The additional waves of these potentials may reflect the augmented cortical reactivity during slow wave state of sleep. Both the EEG and the forms of evoked potentials were qualitatively similar in wakeful phase and paradoxical phase of sleep suggest that the two phases have some common synaptic mechanisms. Lesions of the area lateral to nucleus tr. spinalis n. trigemini abolished ipsilateral eye movements selectively during the paradoxical phase of sleep and not during alert state. The movements, however, became normal by about the seventh day following lesioning. The basis of the effect was not identified. From the features of the evoked potentials and the dynamogenic effects it is, however, discussed that the effects of the region may be due to reticular and any sensory elements likely to be involved.