Functional relationship between cat brainstem neurons during sleep and wakefulness

The neurophysiology of sleep and waking: intracerebral connections, functioning and ascending influences of the medulla oblongata

This paper focuses on the successive historical papers related to medulla oblongata (M.O.) intracerebral connections, its activities and ascending influences regulating sleep waking behavior. The M.O. certainly influences the quantitative and qualitative processes of waking. However, its neurophysiological properties are often concealed by those of the upper-situated brain stem structures. The M.O., particularly the solitary tract nucleus, is involved in sleep-inducing processes. This nucleus seem to act as a deactivating system of the above situated reticular formation, but it also impacts directly on the thalamocortical slow wave and spindle-inducing processes. The M.O. is significantly involved in paradoxical sleep mechanisms. Indeed, the mesopontine executive centers are unable to induce paradoxical sleep without the M.O. Moreover, stimulation of the solitary tract nucleus afferents can induce paradoxical sleep, and the M.O. metabolic functioning is specifically disturbed by paradoxical sleep deprivation. Finally. there seems to be a paradoxical sleep Zeitgeber. Our current knowledge shows that this lowest brain stem level is crucial for sleep waking mechanisms. It will undoubtedly be further highlighted by future electrophysiologial and neurochemical studies.

Attenuation during paradoxical sleep of signals from tooth pulp to thalamus

Quantitative evaluation of the response of thalamic neurons to tooth pulp stimulation was made in chronically prepared cats. The latency, duration and intensity of the responses were measured from the post-stimulus time histograms to estimate, from various aspects, the alteration in the responsiveness during different phases of sleep and wakefulness. During slow wave sleep, tooth pulp-evoked impulses tended to be transmitted to the thalamus in a similar or slightly higher intensity compared to wakefulness. In contrast, during paradoxical sleep the signals were often attenuated in many aspects. The results seem to be in favor of the idea that the impairment of signal to noise ratio in a variety of neuronal networks is one of the characteristics of paradoxical sleep.