Memory problems alone, however, do not appear to be the whole story. In a new paper for Sleep Medicine Reviews, Peter Fazekas of the University of Antwerp and colleagues instead suggest that white dreams are better understood as a diminished form of consciousness. According to this hypothesis, white dreaming is a bit like watching a badly tuned TV, with the volume muted: The sleeper really is dreaming, but the signal is too weak to establish any definite details beyond the vaguest impressions.
Fazekas’s previous research focused on the variations in waking consciousness, such as the vividness of a sensory experience. In so-called masking experiments, for example, researchers quickly flash one image, “the target,” before the participants’ eyes, followed by another picture, “the mask.” Sometimes the participants have a clear impression of the target—a cat, say—while at other times its presentation is too quick for conscious perception; they only see the mask.
Read: A new theory explains how consciousness evolved
Between those extremes, however, many participants report a vague sense of having seen something, without being able to give the details of what it is. This sense of vividness—or lack of it—usually correlates with activity in the posterior regions at the back of the brain. The greater the high-frequency activity in this area, the richer and more detailed the experience, while muted activity corresponds to the weaker impressions.
Perhaps, Fazekas hypothesized, white dreams are similar to those minimal forms of conscious awareness. Working with Georgina Nemeth at Eotvos Lorand University in Hungary and Morten Overgaard at Aarhus University, he took another look at Siclari’s data to see whether this was true. They noticed that Siclari’s statistical analysis had unintentionally obscured some potentially important differences in the posterior brain activity between white dreams, remembered dreams, and the sensation of having not dreamed at all. Sure enough, a reanalysis of the raw data suggested that white dreams do indeed reflect a striking reduction in that posterior brain activity, compared with remembered dreams, but still greater activity than when participants report no dreaming experience at all.
The reduced frontal and central activity that Siclari observed would naturally follow from this, Fazekas believes, since those regions would have little information to encode into a memory. “For those areas to turn on, so to speak, you need an intense experience, which you don’t have in the white dream,” Fazekas says.
Siclari agrees that Fazekas offers a feasible interpretation of her data, though she believes that the reduced recall is still the primary distinguishing feature of white dreams. When prompted to dig deeply into their memories, she says, some participants were later able to draw details from those apparently content-less experiences, which suggests that in at least some cases, it is purely a failure of recall.