Sleep and other behavioural responses induced by acetylcholinic stimulation of frontal and mesial cortex

Abstract

With the aim of mapping out the possible existence of hypnogenic areas in the frontal and mesial cortex, microcrystals of acetylcholine were applied through cannulae permanently implanted in awake unrestrained cats. The behavioural responses to the chemical stimulus were simultaneously monitored by several electrophysiological indices such as the electrical activity of the neo- and entorhinal cortex, eye movements and the EMG of the nuchal muscles. It was found: That acetylcholine elicited all the behavioural and electrographic manifestations of the two patterns of sleep from well defined cortical areas including mainly the gyrus coronalis, the gyrus proreus, the posterior and anterior sygmoid gyri, as well as the anterior limbic cortex in the mesial surface of the hemisphere. That local atropinization prevented sleep otherwise produced by low frequency stimulation of the same cortical loci in the orbitofrontal cortex. That electrolytic lesions destroying the medial forebrain bundle at the preoptic region, prevented sleep formerly elicited by acetylcholinic stimulation of the same frontal and anterior limbic cortical areas. It is concluded that the disclosed hypnogenic frontolimbic cortical areas have anatomical connections with the limbic-midbrain hypnogenic circuit forming part of the corticofugal descending limb of a cholinergic sleep system.