This study, based on a large representative sample of the US general population, is the first to demonstrate the prevalence of nocturnal wandering in the community. Precisely, 3.6% of the sample had more than 1 episode of nocturnal wandering in the previous year. Apart from a study we did 10 years ago in the European general population,7
where we reported a prevalence of 2% of sleepwalking, there are nearly no data regarding the prevalence of nocturnal wanderings in the adult general population. In the United States, the only prevalence rate was published 30 years ago. This study reported a prevalence of 2.5% of sleepwalking in a sample of 1,006 adults living in the Los Angeles metropolitan area.6
There are several noteworthy results in our study. Sleep fragmentation was proposed as a marker for sleepwalking.12,29,30
In our study, however, nocturnal awakenings were significantly associated with nocturnal wanderings only in bivariate analyses. It became nonsignificant in the multivariate model, which means that the association is explained by other factors, such as obstructive sleep apnea syndrome. Recent controlled clinical studies have shown that a large proportion of sleepwalkers also have sleep-disordered breathing and that sleepwalking disappears once affected individuals are treated for the breathing disorder.31,32
Furthermore, sudden arousals from slow-wave sleep were found to have a low specificity for NREM parasomnias.29
Additionally, one should keep in mind that in this study, nocturnal awakenings were based on self-report; we could not therefore account for arousals or microarousals because the participants were unaware of them. This would suggest that the sleep fragmentation in sleepwalkers might be mostly in the form of arousals and microarousals rather than complete awakenings.
Sleep restriction was also reported as a possible trigger for sleepwalking episodes.13,33
In this study, we did find a higher risk of having at least 1 nocturnal wandering episode in the previous year in individuals sleeping less than 7 hours per night after adjusting for possible confounding factors such as age, sleep, and mental disorder.
Several cases of sleepwalking associated with the intake of psychotropic medication (antidepressant, hypnotic, normothymic, neuroleptic) have been reported in the literature.14,15
However, these reports remain incidental. For most of these cases, it is impossible to tell whether the patient was sleepwalking or had episodes of nocturnal wandering (i.e., the patient is awake but is confused and has no memory of the episode upon awakening). Many of these patients had complex medical and psychiatric histories and were heavily medicated. Consequently, the causality between the use of a specific psychotropic medication and the appearance of sleepwalking episodes is not as obvious as it may appear. Furthermore, our results show that individuals taking psychotropic medication (antidepressants, anxiolytics, or hypnotics) were having nocturnal wandering episodes for as long as those without medication. Consequently, it seems unlikely that these medications cause nocturnal wandering, but rather that they appear to trigger events in predisposed individuals. We did find a higher risk of frequent nocturnal wandering episodes among individuals with insomnia disorder but not with hypnotic intake (benzodiazepine or benzodiazepine-like hypnotics). This suggests, as mentioned earlier, that sleep restriction or sleep fragmentation (because of the insomnia) might be involved in sleepwalking and nocturnal wandering.
It has been suggested that the serotonergic system may be involved in sleepwalking.34
In our study, the associations between SSRI antidepressants, major depressive disorder, obsessive-compulsive disorder, obstructive sleep apnea syndrome, and nocturnal wandering would support the hypothesis of a serotonin involvement in sleepwalking. Studies have not been carried out examining the relationship between sleepwalking and depression and obsessive-compulsive disorder while controlling for the effects of antidepressant medications. The same conclusion can be drawn for most mental disorders. There are several case reports of medications appearing to induce sleepwalking in psychiatric patients but almost no studies that have examined the incidence of mental disorders in sleepwalking individuals or vice versa. We have recalculated the multivariate models excluding all participants who were treated with a psychotropic drug to verify if the observed associations remained significant. They all remained significant. Therefore, the association between major depressive disorder and nocturnal wandering could not be attributed to the intake of a psychotropic medication. This was the same for obsessive-compulsive disorder: the association persisted in the absence of psychotropic treatment.
We also found that nearly one-third of individuals with nocturnal wandering had a family history of such disorder. A strong familial occurrence has often been reported in sleepwalking; for example, a prospective study35
reported a sleepwalking occurrence of 14% in children aged between 8 and 10 years who had 1 of their parents with sleepwalking history and 2% of sleepwalking in children with nonsleepwalking parents. The Finnish cohort twin study reported a higher concordance among monozygotic compared to dizygotic twins and another study has shown a 10-fold increase of sleepwalking among first-degree relatives of sleepwalkers compared to the general population.36
Recently, a genetic study highlighted that sleepwalking appears to be an autosomal dominant disorder with reduced penetrance and with chromosome 20q12-q13.12 localization for a gene responsible for the disorder.37
It should be kept in mind, however, that our results are based on subjective reports. Since ours is an epidemiologic study, we did not conduct laboratory testing with respondents to confirm diagnoses. Sleepwalking, however, does not require polysomnographic recording to confirm the diagnosis. However, given the absence of objective measures of sleepwalking, because complete or partial amnesia is one of the characteristics of this sleep disorder, it is likely that sleepwalking was underreported, especially among participants living alone. Nonetheless our data provide critical information regarding this understudied sleep disorder.
Historically, sleepwalking has been believed to be associated with psychological or psychiatric conditions, particularly if it begins in, or persists into, adulthood. This study supports the organic nature of sleepwalking, and underscores the fact that sleepwalking is much more prevalent in adults than previously appreciated. It is now clear that sleepwalking represents an admixture of wakefulness and sleep, supporting the fact that sleep is not a global, whole-brain phenomenon.38–40