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figure 13.1 REM sleep polysomnograms demonstrating the necessity of extensive extremity EMG monitoring in documenting RBD. (A) Shows customary REM sleep, with its distinct electrophysiological profile: the triad of dense, high-voltage REMs (1 -2), activated EEG (3-5), and chin EMG atonia with one minor burst of phasic twitching (6). Channels 1 -6 are sufficient for scoring sleep stages throughout the night, according to the standard methods and criteria of Rechtschaffen and Kales. However, (B) contains identical channels 1-6 from (A) and reveals that extensor and flexor EMGs of the four limbs have excessive twitching. EKG rate (15) remains constant and respirations (16) are mildly irregular. (Adapted from Mahowald, M. W„ and Schenck, C. H. (1990). REM Sleep Behavior Disorder, In Handbook of Sleep Disorders, M. J. Thorpy, ed., p. 567, New York: Marcel Dekker, with permission.)

figure 13.1 REM sleep polysomnograms demonstrating the necessity of extensive extremity EMG monitoring in documenting RBD. (A) Shows customary REM sleep, with its distinct electrophysiological profile: the triad of dense, high-voltage REMs (1 -2), activated EEG (3-5), and chin EMG atonia with one minor burst of phasic twitching (6). Channels 1 -6 are sufficient for scoring sleep stages throughout the night, according to the standard methods and criteria of Rechtschaffen and Kales. However, (B) contains identical channels 1-6 from (A) and reveals that extensor and flexor EMGs of the four limbs have excessive twitching. EKG rate (15) remains constant and respirations (16) are mildly irregular. (Adapted from Mahowald, M. W„ and Schenck, C. H. (1990). REM Sleep Behavior Disorder, In Handbook of Sleep Disorders, M. J. Thorpy, ed., p. 567, New York: Marcel Dekker, with permission.)

effect. These cats also displayed de novo "hallucinatory-type" behaviors during REM sleep that strongly resembled "oneirism" (i.e., dream-enactment). The oneiric behaviors in these cats always occurred during unequivocal REM sleep, with REM sleep retaining all its defining features (apart from loss of REM-

atonia): cortical EEG activation; unresponsiveness to environmental stimuli; periodic cycling with NREM sleep; ponto-geniculo-occipital (PGO) waves; pronounced myosis; and relaxation of the nictitating membranes. Thus, the mechanisms responsible for the oneiric behaviors were postulated to result from disruption of brain neuronal organization during REM sleep.

Further work by Jouvet's group on "paradoxical sleep without atonia" revealed that a stereotypic repertoire of behaviors was displayed, without external provocation, during REM sleep. Attack behavior was most commonly displayed, and sexual or feeding behaviors were never observed (Sastre and Jouvet, 1979; Jouvet et al., 1981). These cats were never inappropriately aggressive during wakefulness—a finding mirrored in human RBD.

Morrison's group, in addition to Jouvet's group, has identified four categories of oneiric behaviors in the cat model of RBD (Henley and Morrison, 1974; Morrison, 1979; Hendricks et al., 1982). The appearance of each behavioral category is dependent on the location and size of the pontine tegmental lesions (Hendricks et al., 1982): (1) minimal syndrome of generalized limb or truncal twitching and jerking, which can intermittently become prominent and violent; (2) orienting and exploratory behaviors, involving staring, head raising, head turning, grasping, and searching; (3) stalking imaginary prey, and episodic attack behavior; and (4) locomotion.

These animal experiments revealed that loss of REM-atonia alone is insufficient to generate RBD. There also must presumably be disinhibition of motor pattern generators in the mesencephalic locomotor region to result in phasic motor overactivation with behavioral release during REM sleep (Morrison, 1979; Hendricks et al., 1982). Studies in dogs have identified a colocalization of the atonia and locomotor systems in the pons, thus providing an anatomic basis for the simultaneous dysregulation of the tonic and phasic motor systems in RBD (Lai and Siegel, 1990).

Supraspinal mechanisms responsible for REM-atonia originate in the perilocus ceruleus (LC)-alpha nucleus of the pons that then excite neurons of the nucleus reticularis magnocellularis in the medulla, which then transmit descending inhibitory projections—more powerful than the competing descending excitatory projections—to the spinal alpha motoneurons, resulting in hyper-polarization and resultant muscle atonia (Pompeiano, 1976; Sakai et al., 1981). Therefore, REM-atonia results from an active process involving a specific neuronal circuitry and is not the result of passive cessation of motor activity.

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