Out-of-body experiences in relation to lucid dreaming and sleep paralysis: A theoretical review and conceptual model.

Out-of-body experiences (OBEs) are characterized by the subjective experience of being located outside the physical body. Little is known about the neurophysiology of spontaneous OBEs, which are often reported by healthy individuals as occurring during states of reduced vigilance, particularly in proximity to or during sleep (sleep-related OBEs). In this paper, we review the current state of research on sleep-related OBEs and hypothesize that maintaining consciousness during transitions from wakefulness to REM sleep (sleep-onset REM periods) may facilitate sleep-related OBEs. Based on this hypothesis, we propose a new conceptual model that potentially describes the relationship between OBEs and sleep states. The model sheds light on the phenomenological differences between sleep-related OBEs and similar states of consciousness, such as lucid dreaming (the realization of being in a dream state) and sleep paralysis (feeling paralyzed while falling asleep or waking up), and explores the potential polysomnographic features underlying sleep-related OBEs. Additionally, we apply the predictive coding framework and suggest a connecting link between sleep-related OBEs and OBEs reported during wakefulness.

Out-of-body illusion induced by visual-vestibular stimulation.

Out-of-body experiences (OBEs) are characterized by the subjective feeling of being located outside one's physical body and perceiving one's own body from an elevated perspective looking downwards. OBEs have been correlated with abnormal integration of bodily signals, including visual and vestibular information. In two studies, we used mixed reality combined with a motion platform to manipulate visual and vestibular integration in healthy participants. Behavioral data and questionnaires show that congruent visual-vestibular stimulation in a self-centered reference frame induced an OBE-like illusion characterized by elevated self-location and feelings of disembodiment and lightness. The OBE-like illusion was also modulated by individuals' visual field dependency assessed by the Rod and Frame Test. These results show that the manipulation of visual-vestibular stimulation in the present study induces various aspects of OBEs and further link OBE to congruency mechanisms between visual and vestibular gravitational and self-motion cues.

Physical Body Orientation Impacts Virtual Navigation Experience and Performance.

Most human navigation studies in MRI rely on virtual navigation. However, the necessary supine position in MRI makes it fundamentally different from daily ecological navigation. Nonetheless, until now, no study has assessed whether differences in physical body orientation (BO) affect participants' experienced BO during virtual navigation. Here, combining an immersive virtual reality navigation task with subjective BO measures and implicit behavioral measures, we demonstrate that physical BO (either standing or supine) modulates experienced BO. Also, we show that standing upright BO is preferred during spatial navigation: participants were more likely to experience a standing BO and were better at spatial navigation when standing upright. Importantly, we report that showing a supine virtual agent reduces the conflict between the preferred BO and physical supine BO. Our study provides critical, but missing, information regarding experienced BO during virtual navigation, which should be considered cautiously when designing navigation studies, especially in MRI.

Five-year follow-up study of tooth extraction after nonsurgical endodontic treatment in a large population in Taiwan.

BACKGROUND/PURPOSE: Nonsurgical retreatment, apical surgery and tooth extraction are three major untoward events following nonsurgical root canal treatment (NSRCT). The purpose of this study was to assess untoward events and total tooth extraction after NSRCT in a large population of dental patients in Taiwan. METHODS: A total of 1,588,217 teeth treated with NSRCT in Taiwan in 2000 were analyzed for the first untoward event and total tooth extraction over a 5-year follow-up period. RESULTS: The first untoward event occurred in 192,488 (12.1%) teeth within the first 5 years posttreatment. Nonsurgical retreatment was performed on 69,273 (36.0%) of these teeth, 4741 (2.5%) received apical surgery, and 118,474 (61.5%) were extracted. In addition, 1,463,312 (92.1%) teeth treated with NSRCT were retained in the oral cavity, and 124,905 (7.9%), including 24,499 (19.6%) anterior teeth, 33,356 (26.7%) premolars, and 67,050 (53.7%) molars were extracted within the 5 years of follow-up. Of these 124,905 teeth, 5869 (4.7%) were extracted after nonsurgical retreatment, 562 (0.4%) after apical surgery, and 118,474 (94.9%) after the first untoward events. There were significantly more molars (54.5% vs. 43.3%) and significantly fewer anterior teeth (19.0% vs. 27.5%) extracted in private clinics than in hospitals (p<0.001). The overall tooth extraction rate was significantly greater in hospitals (10.0%) than in private clinics (7.7%, p<0.001). However, tooth extraction procedures were almost evenly distributed over the 5-year follow-up period, with the annual incidence being close to 20%. The overall mean tooth extraction time was significantly greater in private clinics (2.52+/-1.43 years) than in hospitals (2.29+/-1.50 years, p<0.001). CONCLUSION: We conclude that tooth extraction (61.5%) is the most common of the three untoward events, and approximately 95% of tooth extractions are performed at the time of the first untoward event. NSRCT is still a valuable dental procedure in Taiwan because of the high rate (92.1%) of tooth retention after 5 years of follow-up.

First untoward events and reasons for tooth extraction after nonsurgical endodontic treatment in Taiwan.

In this study, 857 teeth having undergone nonsurgical root canal treatment (NSRCT) in Taiwan in 2000 were evaluated during a 5-year follow-up period for first untoward events and reasons for tooth extractions. First untoward events occurred in 83 (9.7%) teeth during this follow-up period, and nonsurgical retreatment was performed for 20 (24.1%), 4 (4.8%) received apical surgery, and 59 (71.1%) were extracted. By the end of this 5-year follow-up period a total of 64 (7.5%) teeth had been extracted. There were 65 reasons for tooth extraction given by the 56 performing dentists who responded to the extraction reason questionnaires; 6 (10.7%) were attributed to endodontically related diseases, 15 (26.8%) to periodontal diseases, 26 (46.4%) to large decay or unrestorable tooth, and 18 (32.1%) to tooth fracture. The conclusion was that 7.5% of the NSRCT teeth were extracted by the end of the 5-year follow-up period, and only 10.7% of these teeth were extracted as a result of endodontically related diseases.