Several paradigms of perceptual learning suggest that practice can trigger long-term, experience-dependent changes in the adult visual system of humans. As shown here, performance of a basic visual discrimination task improved after a normal night's sleep. Selective disruption of rapid eye movement (REM) sleep resulted in no performance gain during a comparable sleep interval, although non-REM slow-wave sleep disruption did not affect improvement. On the other hand, deprivation of REM sleep had no detrimental effects on the performance of a similar, but previously learned, task. These results indicate that a process of human memory consolidation, active during sleep, is strongly dependent on REM sleep.

Medullary disorders can be associated with a sleep apnea syndrome. The present patient developed a sleep apnea syndrome with approximately 25 episodes of apnea or hypopnea during each hour of sleep following a lateral medullary infarction. The presence of predisposing factors and involvement of respiratory centers in the area of the medullary lesion may determine the appearance of sleep apnea with brainstem infarction. Investigation of breathing during sleep may be helpful in such cases. (Stroke 1988; 19:637-639) T he respiratory neurons are located in the reticular formation of the medulla oblongata. They are closely related to motor activity centers of the upper respiratory tract involving the tongue and pharynx. The larynx ventilation undergoes changes during rapid eye movement (REM) and non-REM sleep as a consequence of changes in the reticular system of the medulla oblongata.' The anatomic proximity of the centers controlling breathing, sleep, and upper respiratory tract motility suggests a close physiologic interrelationship. Sleep in general and REM sleep in particular depress upper respiratory tract motor function, favoring and accentuating respiratory disturbances.Sleep apnea has been reported in medullary infarction, high cervical cordotomy, syringobulbia, bulbar poliomyelitis, olivopontocerebellar degeneration, neardrowning, neoplasms, hindbrain abnormalities, multiple sclerosis, and trauma (Table I).2 "' 9 Of the medulla oblongata disorders, vascular disturbance is the most frequent cause of respiratory sleep distress.2 " 516 Case Report .'i 49-year-old man with no history of hypertension or obesity suffered a left Wallenberg's syndrome. The clinical signs consisted of hoarse voice, intractable hiccup, left Horner's syndrome, mild skew deviation, left soft palate palsy, left vocal cord paralysis, ataxia (left more than right), right dissociated hemianalgesia with no left face hemianalgesia, right Babinski's sign, and Romberg's sign. Following the stroke the patient had severe difficulty in swallowing. Routine laboratory examinations were normal. Computed tomography (CT scan) with and without contrast done at the time of admission showed no abnormality. Fine cuts through the posterior fossa could not be obtained because of temporary technical limitations.During the next 10 days, as his swallowing disturbance improved, very noisy snoring appeared, with abrupt pauses accounting for apneic spells. An earnose-throat examination revealed a long uvula and a septum deviation occluding his left nostril. Based on anamnestic data collected from his wife, there was no history of loud snoring or respiratory arrest before the brainstem stroke. Sleep was monitored for two nights following an adaptation night, using a routine polygraphy technique. The routine porygraphy consisted of electroencephalography, electro-oculography, electromyography, breathing monitoring, and closedcircuit television. Breathing monitoring consisted of nasal-oral airflow, rib-abdominal cages, and ear oximetry. The mean data for two nig...

Despite the fact that yawning is a reality of everyday life, its study is not included in the curriculum of medical schools, and most medical textbooks barely mention its existence. Two factors may help to explain this puzzling situation: (a) yawning's borderline position between psychology and neurology, and (b) researchers' lack of understanding as to why people yawn. After review of the literature and personal observation, it is concluded that yawning is a complex arousal defense reflex located in the reticular brainstem with a peripheral and central arche, whose aim is to reverse brain hypoxia. Yawning occurs with loss of interest (boredom) and may or may not be associated with fatigue. By reversing drowsiness, yawning avoids a decreased concentration capacity resulting from borderline hypoxia. It is hoped that this article will stimulate further research on the phenomenon.

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Non-REM sleep transforms the waking alternating Parkinsonian tremor into subclinical repetitive muscle contractions whose amplitude and duration decrease as non-REM sleep progresses from stages I to IV. During REM sleep Parkinsonian tremor disappears while the isolated muscle events increase significantly.