H. W. Magoun

Brain stem reticular formation and activation of the EEG

1. Stimulation of the reticular formation of the brain stem evokes changes in the EEG, consisting of abolition of synchronized discharge and introduction of low voltage fast activity in its place, which are not mediated by any of the known ascending or descending paths that traverse the brain stem. The alteration is a generalized one but is most pronounced in the ipsilateral hemisphere and, sometimes, in its anterior part. 2. This response can elicited by stimulating the medical bulbar reticular formation, pontile and midbrain tegmentum, and dorsal hypothalamus and subthalamus. The bulbar effect is due to ascending impulses relayed through these more cephalic structures. The excitable substrate possesses a low threshold and responds best to high frequencies of stimulation. 3. Some background synchrony of electrocortical activity is requisite for manifestation of the response. In the encephale isolé, reticular stimulation has no additional effect upon the fully activated EEG. With synchrony, in spontaneous drowsiness or light chloralosane anesthesia, the effect of reticular stimulation is strikingly like Bergers alpha wave blockade, or any arousal reaction. In full chloralosane anesthesia, high voltage slow waves are blocked but no increase in lower amplitude, fast activity occurs. With barbiturate anesthesia, the reticular response is difficult to elicit or is abolished. 4. In the chloralosane preparation, the secondary cortical response evoked by a sensory volley is generally unaffected by reticular stimulation. Consequent sensory after-discharge is abolished, however, as is pyramidal tract discharge and jerky movements referable to it. Outside the sensory receiving area, secondary responses themselves may be reduced or prevented. 5. The convulsive spikes produced by local strychnine and those of a fit following supramaximal cortical excitation, are not decreased by stimulating the reticular formation. 6. The cortical recruiting response induced by low frequency stimulation of the diffuse thalamic projection system is reduced or abolished by reticular stimulation. 7. There is some indication that the cortical effect of reticular stimulation may be mediated by this diffuse thalamic projection system, for synchronized activity within it is similarly prevented by reticular excitation, and direct high frequency stimulation of this system, within the thalamus, reproduces the reticular response. It is possible, however, that other mechanisms may be involved in its mediation. 8. The reticular response and the arousal reaction to natural stimuli have been compared in the encéphale isolé, in which EEG synchrony was present during spontaneous relaxation or was produced by recruiting mechanisms, and the two appear identical. 9. The possibility that the cortical arousal reaction to natural stimuli is mediated by collaterals of afferent pathways to the brain stem reticular formation, and thence through the ascending reticular activating system, rather than by intra-cortical spread following the arrival of afferent impulses at the sensory receiving areas of the cortex, is under investigation. 10. The possibility is considered that a background of maintained activity within this ascending brain stem activating system may account for wakefulness, while reduction of its activity either naturally, by barbiturates, or by experimental injury and disease, may respectively precipitate normal sleep, contribute to anesthesia or produce pathological somnolence.

Effect upon the EEG of acute injury to the brain stem activating system

The effect upon the EEG in the unanesthetized ecéphale isolé of acute brain stem lesions in a position to involve the ascending reticular activating system has been studied. Elimination of the bulbar segment was without marked effect. Some synchronization followed elimination of the pons, but the most pronounced and prolonged changes occurred as a result of mesencephalic transection, or of discrete injury to the midbrain tegmentum or basal diencephalon, following which the EEG activation pattern of low voltage fast activity was reduced or abolished and the cortical record became dominated by recurring bursts or spindles of high voltage slow waves like those of normal sleep or barbiturate anesthesia. Bursts could be recorded from the intralaminar and other nuclei of the thalamus and these thalamic bursts were abolished by acute decortication. Conversely, cortical bursts were abolished by acute thalamic lesions. Possible interrelations of these regions in this activity is discussed. These results offer an explanation for the clinical observation of somnolence following basal injury to the brain, and suggest that a maintained influence of the ascending brain stem activating system underlies wakefulness, while absence of this influence precipitates sleep.

Behavioral and EEG changes following chronic brain stem lesions in the cat.

Abstract The effect upon behavior and the EEG of chronic lesions in the rostral brain stem has been studied in a series of cats. Of lesions in sensory paths, in the periaqueductal grey, or in the midbrain tegmentum and basal diencephalon, only the latter, in a position to interrupt the ascending reticular activating system, were followed by chronic somnolence and EEG synchrony. Activation of the synchronized EEG by somatic and auditory stimulation was still possible either after the reticular activating system or after long sensory paths had been interrupted immediately behind the thalamus. Collateral sensory excitation of the reticular activating system in the lower brain stem, and the direct arrival of afferent impulses at some site above the midbrain, thus serve equally well to induce EEG arousal, but only in the former instance does prolonged wakefulness follow. Poverty of behavior after lesions of the reticular activating system suggests that its influences may be directed both cephalically to activate the EEG and caudally to facilitate motor activity, in maintaining the waking state.

Augmentation of evoked electro-cortical activity during spindle bursts

Abstract Several types of evoked electro-cortical activities have been observed to undergo pronounced augmentation during spindle bursts and depression during the inter-burst period. The alternation is attribute to a periodic waxing and waning of background excitability, of which the burst may be a manifestation rather than a cause.

John B. Watson and the study of human sexual behavior

Abstract This article reviews the steps in John B. Watsons career from his initial experiments in rat learning, through studies of reflexes in newborn and infant children, to his exploration of adult human sexual behavior. The latter began with questionnaire studies of World War I films on sex hygiene. Watson was next reported to have engaged in laboratory studies of human sexual behavior at The Johns Hopkins University. Subsequently, “a set of small instruments for measuring the female sex response,” stated to have been Watsons, came to light. A photograph and descriptions of these instruments are presented. Other indications of Watsons interests in human sexual behavior, and the early hazards of undertaking such research in academia, are briefly surveyed.