Forebrain mechanisms related to internal inhibition and sleep

In experiments performed on cats and monkeys over the past nine years a “forebrain inhibitory system” has been investigated through recording of neurophysiologic, behavioral, reflexive and intracellular parameters. This forebrain system is capable of expressing its inhibitory influences widely throughout the body, and on both somatic and visceral mechanisms. Electrical stimulation within this system has been shown to: a) suppress ongoing behavior, synchronize the EEG and induce the initial stages of sleep. These behavioral effects could be conditioned to indifferent stimuli. Other studies have shown that lesions within this system result in marked alterations in sleep patterns and in behavioral hyperactivity,b) Inhibit remarkably monosynaptic and polysynaptic reflexes in the brain stem and at cervical and lumbosacral levels of the spinal cord.c) Induce hyperpolarizing potentials within motoneurons of the final common path. Cl infusion caused the hyperpolarization to change to depolarization. Studies of the “forebrain inhibitory system” indicate that at least in part it is a descending system involving both multisynaptic (loop) pathways and direct pathways. It is felt that descending circuits from the forebrain to inhibitory centers in the medulla are responsible for the effects observed at the final common paths from stimulation in the forebrain. It has been found that behaviorally, reflexively and intracellularly, the “forebrain inhibitory system” acts generally in opposition to the reticular activating system of the brain stem, and that the achievement of an organism’s overt behavioral patterns depends on the functional state of both systems.