There is a brief time, between waking and sleep, when reality begins to warp. Rigid conscious thought starts to dissolve into the gently lapping waves of early stage dreaming and the world becomes a little more hallucinatory, your thoughts a little more untethered. Known as the hypnagogic state, it has received only erratic attention from researchers over the years, but a recent series of studies have renewed interest in this twilight period, with the hope it can reveal something fundamental about consciousness itself.
Traditionally, the hypnagogic state has been studied as part of the sleep disorder narcolepsy, where the brain’s inability to separate waking life and dreaming can result in terrifying hallucinations. But it’s also part of the normal transition into sleep, beginning when our mind is first affected by drowsiness and ending when we finally lose consciousness. It is brief and often slips by unnoticed, but consistent careful attention to your inner experience after you bed down can reveal an unfolding mindscape of curious sounds, abstract scenery, and tumbling thoughts. This meandering cognitive state results from what Cambridge University researcher Valdas Noreika calls a “natural fragmentation of consciousness” and the idea that this can be tracked over the early minutes of sleep entry is the basis of recent hypnagogia research.
A recent proof-of-principle study, led by Noreika, intensively studied a single individual as he repeatedly transitioned into sleep while the brain’s electrical activity was recorded using EEG scalp electrodes. The would-be-sleeper was asked to press a button when he experienced an intrusive thought or image, and to verbally report it to the sleep researchers. The descriptions were pleasantly bizarre: “putting a horse into a sort of violin case and zipping it up,” “the phrase learning to consume consciously from a master,” “visual image of a curled up music manuscript.”
The electrical activity of the brain became steadily more predictable the longer the person lay still—something that’s entirely normal for sleep entry. Unexpectedly though, the hypnagogic intrusions were preceded not by sudden bursts of complex brain activity, like sparks in a fading candle, but by sudden changes to a more orderly brain state. Noreika is working on the hypothesis that when we enter sleep, the brain steadily dismantles the models and concepts we use to interpret the world, leading to moments of experience unconstrained by our usual mental filters.
This is intuitively appealing and would fit with one of the most curious aspects of the hypnagogic experience: Our thoughts can stray towards tumbling horses, zips and violins but they also can seem completely unremarkable, and indeed, entirely reasonable, until we are jolted from our reverie. Only at this point do they seem odd or out-of-context.
The difficulty that people have detecting the strangeness of these experiences prompted psychologists Clemens and Jana Speth, both at the University of Dundee, to examine reports of hypnagogic intrusions. As Clemens says, the two were hoping “to develop a timeline that shows what elements of consciousness decline or emerge as people drift into sleep.” Applying linguistic analysis to data from a sleep lab, they found evidence that reflective thought—the ability to evaluate ongoing experience—declined quickly during the hypnagogic state while thoughts about physical interaction with the imaginary world increased, indicating a change in the structure and not just the content of conscious thought.
Similarly, by comparing the hypnagogic state to REM dreaming, a 2013 study by the same researchers confirmed the long-noted observation that while dreams often feel fully immersive, hypnagogia tends to be experienced as if we were passive observers—with the hallucinatory thoughts and images occurring as a projection on our existing sense of reality. (In a famous passage on hypnagogia in Oliver Twist, Dickens wrote of “the visionary scenes that pass before us.”) The fact that our sense of immersion and reflective distance from our own experience do not always co-occur during sleep may suggest they also have different roles in waking consciousness.
Admittedly, studies from this new wave of interest in hypnagogia are small and still tentative but they reflect a growing trend towards understanding sleep not just as a state of rest and consolidation, but also as a scientific tool for observing the components of consciousness as they are stripped away for entry into slumber. What these studies may be hinting at, is that the brain processes involved in sustaining consciousness might also be central to maintaining a stable, insightful experience of the world—in other words, keeping hallucinations in check.
Francesca Siclari, a sleep and consciousness researcher at the University Hospital of Lausanne, in Switzerland, also hopes this new wave of interest will result in more practical benefits. “The transition to sleep provides a unique opportunity, as one can study how changes in consciousness relate to changes in brain activity,” she says. “This process is not only fundamental to the study of consciousness, it may also shed light on sleep disorders that are associated with an abnormal transition to sleep.”
But there is a more whimsical aspect to this work. Sleep researchers across the world are now dedicated to recording some of the most ephemeral moments of human weirdness, which are often lost to memory after the drama and haze of dream and sleep. Talking bears are being documented. Falling school friends, noted. Researchers are working not only as neuroscientists but also as archivists of the unconstrained mind.