Sleepwalking Déjà Vu

THE ARTICLE OF OUDIETTE ET AL1 PUBLISHED IN THIS EDITION OF SLEEP GIVES OFF A DISTINCT FEELING OF SLEEP SCIENCE DEJA VU. THEIR REPORT OF “dreamlike” mentation in sleepwalkers and night terror patients is similar in many ways to descriptions and theories of sleepwalking that go back hundreds of years. These theories had disappeared from sleep science but now are reappearing, although with a completely different scientific basis. In 1838, Dr. Isaac Ray, the first American Forensic Psychiatrist, wrote with regard to somnambulism: “Whether this condition is really anything more than a cooperation of the voluntary muscles with the thoughts which occupy the mind during sleep, is far from being settled among physiologists.”2 It may seem that we have not advanced far in the last 170 years regarding theories of sleepwalking. However, the trip from 1838 to the present has had many twists and turns. Our scientific understanding of sleepwalking and related disorders has certainly advanced dramatically, especially in the last 10 years.3 But how far have we advanced in understanding the relationship between sleepwalking behavior and the “mind” during sleep? In the middle ages, sleepwalkers were thought to be possessed. In more recent times, prior to the beginning of the modern sleep medicine era in the 1960s, sleepwalking and night terrors were thought to reflect the enactment of dreams driven by prior, repressed psychic trauma. Sleepwalking was most often seen through the lens of psychodynamic or Freudian theory. These theories were most popular before the discovery of REM sleep and before sleepwalkers were studied in modern sleep laboratories.4 Sleep laboratory studies first conducted in the 1960s showed that sleepwalking and night terrors were not disorders of REM sleep, but instead came out of deep NREM sleep following sudden arousals. Many pre-1960 reports of complex behaviors attributed to sleepwalking or night terrors are now thought to have been more likely the result of REM behavior disorder (RBD), a disorder in which the individual enacts REM related dreams.5 However, clinical reports of night terrors have provided a window into what might be going on in the mind of the sleepwalker. Night terrors often begin with a sudden, dreamlike, frightening image that the patient can recall and describe. The subsequent behavior of patients with night terrors often appears to be a response to that initial image.6 Studies of mentation in sleepwalkers have lagged far behind those of pathophysiological and neurophysiological aspects of sleepwalking and night terrors in the last 10 years. Occasional anecdotal reports in single patients have appeared. In my own career I have witnessed an apnea-triggered violent night terror episode, in which the patient partially destroyed the sleep laboratory room.7 When he was asked within an hour of the episode what he remembered he replied “someone was chasing me” and could provide no further details. However, opportunities of this sort are extremely rare and cannot be planned in advance. In the post-1960s era, it has typically been reported that sleepwalkers and night terror patients have no memory for their behaviors. Later, definitions of and criteria for the diagnosis of sleepwalking were modified to say that the sleepwalkers may have fragmentary memories. This change appears related to the substantial growth in sleep medicine and sleep disorders research. Suddenly, the diagnosis of sleepwalking and night terrors was not that rare. Estimates of their incidence now approach 4% in adults,8 which has made case series studies a possibility. In 2006, the first reports of mentation and cognitive function in a group of 34 adult chronic sleepwalkers appeared.9 Zadra and colleagues reported in an abstract that 41% of their population believed their episodes to be related to mentation, and 65% reported a memory of some type of strong emotion. This is now followed by an even more detailed study by Oudiette et al1 in this issue of SLEEP. How should these data be evaluated and integrated into what we now know about sleepwalking? First, the methodological limitations should be considered. Oudiette et al1 reports of dreamlike mentation are for episodes of sleepwalking and night terrors that occurred sometime in the past. There is no way to verify that these dreamlike reports are directly connected to these episodes or whether these episodes in the past were actually sleepwalking or night terror episodes. The proper diagnosis of these past episodes remains educated speculation. Oudiette and colleagues1 correctly address this problem by suggesting these anecdotal studies should be followed by empirical studies. However they also acknowledge this has proven to be extremely difficult in the past. In the real world, sleepwalking and night terrors appear only intermittently and may require a “perfect storm” of factors such as sleep deprivation, stress, and triggers that occur only rarely.3 However, the possibility of conducting laboratory-based studies of sleepwalking and night terrors has increased dramatically in the last 5 years with the publication of a series of studies by Zadra, Montplaisir, and colleagues.10 They have shown that episodes of complex behavior can be elicited in the sleep laboratory using sleep deprivation and audio stimuli. But can these techniques be used to take reports of dreamlike mentation in the sleep laboratory? It is well known that sleepwalkers are extremely hard to awaken. Additionally, in at least one study in which researchers tried to trigger sleepwalking, members of the technical staff were actually physically assaulted by the research subjects in the midst of their episodes.11 This report needs to be approached with an open mind as well as with caution.1 The collection of retrospective anecdotal reports in otherwise well-diagnosed patients may not be the result of the most sophisticated research methods. But in some cases, it may be the only way to collect data. In those cases, replication of another retrospective anecdotal report—as in Zadra et al9—lends power to the notion that sleepwalkers and night terror patients may actually have much more detailed mentation during their episodes than is currently thought; mentation may be a trigger for full blown episodes in some patients or be somehow related to the actual behaviors in others. However, these conclusions are far from certain and will be very difficult to confirm under the best of experimental conditions. We have not come quite full circle on the question of the nature of mentation in sleepwalking and sleep terrors in the last 150 years, but progress has been made. However, the basic question of what goes on in the mind/brain of a sleepwalker has yet to be fully unraveled.