Relationship between the hypnagogic/hypnopompic states and reports of anomalous experiences - sleep

Journal of Parapsychology, The, June, 2002 by Simon J. Sherwood

A whole range of anomalous experiences (1) has been reported during the hypnagogic or hypnopompic states that surround periods of sleep. It is not uncommon for people to experience brief, vivid, and often strange imagery or to find themselves temporarily unable to move or speak during these periods between wakefulness and sleep. These brief sensations and the temporary paralysis are known as hypnagogic or hypnopompic imagery and sleep paralysis, (2) respectively (American Sleep Disorders Association [ASDA], 1990).

Recent surveys found that people who report more childhood experiences of hypnagogic/hypnopompic imagery or sleep paralysis also report a greater number of anomalous experiences during childhood or adulthood (Sherwood, 1999, 2000). More specifically, hypnagogic/hypnopompic imagery has been associated with reports of extrasensory perception (ESP), apparitions and communication with the dead, out-of-the-body experiences (OBEs), visions of past lives, and experiences involving extraterrestrials (e.g., Glicksohn, 1989; Gurney, Myers, & Podmore, 1886; Leaning, 1925; Mavromatis, 1983, 1987; McCreery, 1993; McKellar, 1957; Spanos, Cross, Dickson, & DuBreuil, 1993). In addition to the above anomalous experiences, sleep paralysis has also been associated with reports of psychokinesis (PK) and near-death experiences (NDEs) (Baker, 1992; Green & McCreery, 1994; Rose & Blackmore, 1996; Rose, Hogan, & Blackmore, 1997; Spanos et al., 1993; Spanos, McNulty, DuBreuil, Pires, & Burgess, 1995).

The question is: are the hypnagogic/hypnopompic states conducive to anomalous processes and events or are normal hypnagogic/hypnopompic features being misinterpreted? Perhaps both statements are true? The aim of this article is to consider evidence for each of these possibilities. First, it is necessary to outline the characteristics of the hypnagogic/hypnopompic states and the features of some of the experiences that can occur within them.

CHARACTERISTICS OF HYPNAGOGIC/HYPNOPOMPIC STATES

Most research, both experimental and survey-based, seems to have focused on the hypnagogic state (the period between wakefulness and sleep, i.e., just as a person is falling asleep). Comparatively little research has been carried out on the hypnopompic state (the period between sleep and wakefulness, i.e., just as a person is waking from sleep). Thus, this article focuses mainly on the hypnagogic state. The hypnagogic state, like the sleep state, is fairly complex and contains a number of steps and stages (Mavromatis, 1983; Rechtschaffen, 1994). Hori, Hayashi, and Morikawa (1994) concluded that the sleep onset period is unique and cannot be accurately categorised as either waking or sleeping. It is very difficult to determine the precise point of falling asleep, except by using arbitrary criteria, because the transition is gradual, because the changes are not always synchronised, and because there are large individual differences in when the changes occur (Lavie, 1996; Rechtschaffen, 1994).

During alert wakefulness, eye movements are fairly rapid, and the normal EEC trace consists of irregular waves of high frequency (Bray, Cragg, Macknight, Mills, & Taylor, 1992). As a person relaxes or becomes drowsy, there is an increase in alpha activity (8-12 Hz), and eye movements become slower and less frequent (Parker, 1975; Rechtschaffen, 1994). In fact, the presence of slow eye movements is considered to be an extremely accurate indicator of hypnagogic mentation (Schacter, 1976). Stickgold and Hobson (1994) found that as the period of eyelid movement quiescence lengthens, that is, as the eyelids move less, mentation becomes more dreamlike. This contrasts with the positive association between eyelid movements and dreamlike mentation during REM sleep. As a person passes through the hypnagogic period into the early stages of non-REM sleep, there is a decline in alpha activity and a concomitant increase in slower theta activity (4-7 Hz; Baddia, Wright, & Wauquier, 1994; Bray et al., 1992; Rechtschaffen, 19 94). A person is typically considered to be asleep once they reach Stage 2 sleep, which is characterised by theta activity and the appearance of sleep spindles (Lavie, 1996; Rechtschaffen, 1994). During the transition from wakefulness to sleep, there is also a decrease in muscle tone, a slowing of the heart and respiration rates, a reduction in blood pressure, and an increase in skin temperature (Mavromatis, 1983; Mavromatis & Richardson, 1984; Schacter, 1976). Upon awakening, these changes go in the opposite direction (Mavromatis, 1983).

During the hypnagogic/hypnopompic states, people can experience brief and vivid imagery or sensations in one or more different sensory modalities (e.g., Foulkes & Vogel, 1965; Hori et al., 1994; Mavromatis, 1987; Sherwood, 2001) or temporary paralysis (ASDA, 1990). Recall of hypnagogic imagery has been found to peak around the middle of standard Stage 1 sleep when the EEG mainly consists of theta activity (Hori et al., 1994).