VISIONS OF BLUE OR PURPLE LIGHTS:
A SCIENTIFIC PERSPECTIVE
(c) 2011 Philip T. Nicholson
What happens in the brain when
blue and purple visions appear?
1. MISTS THAT SWIRL AND DRIFT LIKE CLOUDS
(Note: Keep in mind as you read this material that, in order for a human to see these lights, the same brain mechanisms have to become active—even if the visions are initiated by God.)
Overall, the animation accurately depicts the basic "look and feel" of these visions, so they should be immediately recognizable to anyone who's seen them before; there is, however, an important qualification. In the actual vision, the cloud-like mists have textures that are much more delicate and porous than what is depicted here—a real cloud vision looks more like a spider's web, or like a lace cloth, or like the spiral galaxies photographed in outer space.
Stage 3 NREMS begins when the spindle bursts of stage 2 NREMS—the bursts generate the visions of green rings—terminate automatically after 3 to 6 volleys. During stage 3, the dominant sleep rhythm is once again the cortical slow wave, the same brainwave that oscillated during the drowsy transition to sleep. When the pulsations of the cortical slow wave get referred back to vision-relay neurons in the thalamus, those neurons fire spikes, and when those spikes are sent up to the higher-processing centers in the visual system, they register in consciousness as amorphous clouds of light. The combination of the cortical slow wave oscillating at less than 1 Hertz and the spikes discharged by thalamic vision-relay neurons generates a slow, synchronous brainwave that oscillates at delta band frequencies, that is, at frequencies that range between 1 pulse every 2 seconds (0.5 Hz) and 4 pulses per second (4 Hz).
The waves of light that manifest as amorphous, ever-changing, cloud-like mists acquire their shapes from the anatomical circuitry of the vision-relay center in the thalamus (the lateral geniculate nucleus, or LGN). The way this happens can be illustrated using an analogy that accurately reflects the functional anatomy of the LGN. The visual field is made up of all the visual signals that are relayed by the neurons in two LGNs, one located in each hemisphere of the brain. Think of the two LGNs as constituting, in effect, a dome-like structure. All of the neurons that relay visual signals that encode wavelength information—the kind of information needed to produce color sensations—are located at or near the top of the dome and only in that location. When the pulse of the cortical slow wave arrives in the dome, it triggers discharges in the vision-relay neurons in the upper regions of the dome where the neurons that relay information about color are located. This accounts for the relatively circumscribed boundaries of the blue and purple cloud visions. The discharges of the vision-relay neurons that generate the cloud visions display the same patterns as cortical slow waves: "spontaneous, periodic, synchronous bursts" erupt at unpredictable locations and at unpredictable times, expand slowly in unpredictable directions, and then hover in the visual field for short time before disappearing.
2. A BRIGHT "EYE-LIKE" NODE INSIDE THE CLOUD
The video animation accurately depicts the basic "look and feel" of there being a bright node at the center of the cloud visions, but the actual vision has some important differences that distinguish it from the video. The most important difference from the video animation is that the bright central node is constantly fluctuating back and forth between 2 states: the bright node may, at one moment, have a disk shape, i.e., the bright light is more or less uniform, but then, in the next moment, the light ebbs away from the very center of vision, opening up a dark, "pupil-like" space. Now the image has 3 components: the dark "pupil" in the center, then the brighter light, which has turned into an "iris-like" ring surrounding the "pupil," and, surrounding both of these features, the duller light with a porous, web-like texture that forms the main body of the cloud. But then the meditator sees promontories of light project out of the "iris-like" ring of bright light and down into the dark "pupil." These promontories writhe and coil about, then merge into one another, which fills in the dark space and reconstitutes the disk-shaped surface of the bright inner node. This alternation between the solid surface and the eye-like ring continues for as long as the cloud remains in the visual field. Another way the animation is different is that the inner node in the video is white, but in the actual vision the node stands out, not because it is white, but because it presents a brighter, more fine-grained, and more opaque version of the same color of the cloud that surrounds it.
The processes that generate the bright inner "eye-like" formation at the center of the cloud can be illustrated by drawing once again on the analogy that the functional anatomy of the two LGNs forms, in effect, a dome-shaped structure. The vision-relay neurons that encode information about the wavelengths of light—information that the brain needs to generate color sensations—are all located at or near the top of the dome. Now add one detail that accounts for why the cloud-like visions eventually develop an inner core that is brighter, more finely-grained, and more opaque than the rest of the colored mist. The vision-relay cells that encode wavelength information can be subdivided into 2 donut-shaped (annular) bands: there is an inner annulus, which wraps around the uppermost region of the dome which has the most wavelength-encoding vision-relay neurons, and, equally important, these neurons are very densely packed. There is also an outer annulus of wavelength-encoding neurons that surrounds the inner annulus, but in the outer band the neurons are fewer and not so densely packed. When the pulses of the cortical slow wave arriving in the LGN trigger the vision-relay neurons to discharge spikes, the differences in the densities of wavelength-encoding vision-relay neurons have an important impact: when these signals are sent forward to the higher-processing centers and are registered in the consciousness of a meditator, what appears is a vision of a cloud-like mist of relatively dull blue or purple light with porous textures, and then, at the center of that cloud, a core of much brighter blue or purple light that has a very fine-grained, opaque texture which looks somewhat like molten metal.
To explain why the bright light of the inner node ebbs back to open up a dark, "pupil-like" space, yet another detail about the LGN dome structure needs to be added. There is a tiny disk-shaped space at the very tip-top of the dome that contains no vision-relay neurons whatsoever. (In technical terms, this empty point at the top of the dome represents the center of the retina where the density of cones—the retinal receptors that respond to the wavelengths of external light—drops off to zero.) When the pulses of the cortical slow wave are simulating the discharge of the densely-packed wavelength-encoding neurons in the annular band that surrounds that tiny disk-shaped space (thereby generating the brighter light at the core of the cloud), the higher-processing regions in the brain sometimes "complete" or "fill in" what would otherwise be an empty space with light that has the same characteristics as the immediate surroundings. This aspect of the psychophysics of vision explains why the bright node is sometimes seen as if it were being "filled in" while at other times a dark space is opening up—and why the surface of the bright central node appears so unstable.
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