THE SHIFT TO PAROXYSMAL VISIONS:
A SCIENTIFIC PERSPECTIVE
(c) 2011 Philip T. Nicholson
What happens in the brain when
this sequence of visions appears?
1. THE STAR IMAGE
(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.)
The animation presents a very accurate depiction of the tiny, "star-like" image that condenses at the center of the visual field when a meditator induces many blue or purple cloud visions with bright inner "eye-like" nodes.
In order for a tiny, twinkling "star" to condense at the center of a dark visual field, an intense barrage of excitation must be reverberating back and forth in a few of the axons forming the reciprocal circuits that link vision-relay neurons in the thalamus with vision-processing neurons in the primary visual cortex. As the meditator continues to stare at the star image, the intense concentration of excitatory signals in the reciprocal circuits creates a positive feedback loop driven by the meditator's attention. In effect, the star image is a "focus" of excitation that has the potential to trigger a shift to an epileptic-like seizure—but in this case the "epileptic-like focus," instead of being produced by defective neuron assemblies in the person's brain, is being produced by the meditator's intent concentration on the visual field. During stage 3 NREMS, the slow oscillations of delta brainwaves would normally suppress seizures, but this is not a normal situation: the meditator is staring intently the star image without wavering in order to prolong its appearance, and this concentration of attention sets up a positive feedback loop of excitatory signals, signals that are confined within only a few reciprocal circuits. This feedback loop creates an unstable situation.
2. A "TUNNEL" OF DARK, FAST-MOVING RINGS
- The animation that depicts the influx of dark, fast-moving rings streaming in from the perimeter of the visual field is very accurate, except that, in the actual vision, the background color of the visual field becomes very dark—much darker than shown here—and the flow of black rings against a black background is barely perceptible or even subliminal. In either case, this influx generates a powerful sensation of "optic flow" in which people feel as if they are moving physically even though they are not moving. Those people who do perceive the black rings "receding" away from them sense that they're in a dark, moving "tunnel," and that they're either being pulled toward a distant vortex or falling rapidly backward.
- The synchronous spindle waves of stage 2 NREMS, the brainwaves that in normal circumstances put people to sleep, can be easily destabilized. For this to happen, other neurons in the brain have to have become abnormally excitable before the transition to sleep begins—this might happen, for example, if a religious mystic were to spend long hours in nightly prayer vigils that create a substantial sleep deficit.
If sleep spindle mechanisms become destabilized, the inhibitory neurons that are wrapped around the thalamus (i.e., the thalamic reticular nucleus, or RTN) begin firing synchronous spindle bursts at an accelerated pace: instead of firing at the normal rate of 1 burst every 3 to 10 seconds (0.2 Hz), and instead of terminating automatically after a 3 to 6 volleys, the destabilized spindle bursts fire continuously and at a "hypersynchronous" rhythm of 2 to 3 bursts every second (2.0-3.0 Hz), a 10-fold increase from the normal rate (0.2 Hz). The onset of these fast-paced spindle waves represents the outbreak of a hypersynchronous seizure in the reciprocal circuits linking the vision-relay neurons of the thalamus and their target neurons in the primary visual cortices. The fast-paced spindle bursts are one type of hypersynchronous seizure triggered by the destabilization of sleep rhythm oscillators, but there is a second type of hypersynchronous seizure that alternates with the first. The second type of hypersynchronous seizure is exemplified in the next vision to appear—the radiating spray.
- The dark visual field and the "tunnel" effect are produced by an almost continual suppression of the vision-relay cells in the thalamus. The waves of inhibition that the fast-paced spindle bursts impose on the vision-relay cells flow in such rapid succession that the neurons don't have time to recover and fire rebound spikes before the next wave of inhibition rolls over them. As this is happening, meditators see the background color of the visual field become quite dark (because no visual signals are being forwarded to higher-level processing centers), and they also see, or just sense, an influx of black waves pouring into the visual field at a rate of 2 to 3 per second and generating the illusion of a "tunnel."
3. A RADIATING SPRAY OF BEIGE FLECKS
- The animation of the radiating spray is very realistic except that the viewer of a video is excused from experiencing the non-visual, seizure-like symptoms that erupt during the vision of the spray—muscle tremors in the face and extremities and a feeling of being compelled to arch the back and let the mouth fall slack.
- The vision of the radiating spray is generated by the shift from spindle bursts to the second type of hypersynchronous excitation, called "cortical fast-runs." As the name suggests, neuron discharges ripple out in all directions from an epileptic-like "focus" located at the center of the visual field. An apt analogy would be waves in a pond that ripple away from where a stone was thrown. The waves of excitation that form the "expanding epileptic penumbra" triggered in the primary visual cortices by "fast-runs" of neuron discharges get referred back to vision-relay neurons in the thalamus, and it is the reaction of the vision-relay cells that determines what appears in the meditator's visual field.
- When the vision-relay neurons receive waves of excitation generated by the "expanding epileptic penumbra" of "fast-runs," only about 40% of the vision-relay neurons respond by firing spikes. Those neurons that do fire spikes respond directly to the receipt of cortical feedback and are not influenced by what's happening to the neighboring cells. When these spikes get relayed forward to the higher-level processing centers in the visual pathways, they register in consciousness as tiny flecks of light separated from each other. As the "cortical fast runs" keep rippling outward in an "expanding epileptic penumbra," this process keeps on stimulating waves of discharges of vision-relay neurons that flow away from the top of the LGN dome and down its sides. The shape of the dome gives shape to the spikes so that, when the signals they generate are registered in the consciousness of a meditator, the light-flecks flow as if they were rings with expanding diameters—the exact opposite effect of the light-rings generated by spindle-generated light-rings which have shrinking diameters. While meditators see what looks to them like a spray of individual sparks each radiating out along a centripetal trajectory, this is not because each spark of light actually moves along that trajectory; rather, there are many sparks that contribute to this image, each flashing out as a point of light for only the briefest instant, so it is a series of illuminations that creates the illusion of a single spark in motion. A good analogy would be the illusion of motion that occurs when a string of pixels in a computer-generated digital screen are turned on and off in a sequence that creates the illusion that a small spark of light is moving across the screen.
4. A DAWN-LIKE BRIGHTENING AND BLUING
- The hypersynchronous activity in the neuron circuits linking the vision-relay neurons and their target cells in the primary visual cortices sends a barrage of excitation through the visual pathways to the terminal structure in the visual system, the hippocampus. This is a structure that is known to be vulnerable to build-ups of rhythmic discharges, and in this circumstance just this sort of build-up is driven by the receipt of rhythmic discharges from thalamic and cortical networks.
- When a gradual brightening and bluing of the visual field begins to appear and then proceeds to eclipse the vision of the radiating spray, this is evidence that the build-up of hypersynchronous discharges in the hippocampus has become self-sustaining and also strong enough to block the hippocampal processing of any visual signals forwarded from the visual pathways. As a result, the meditator sees a gradual and uniform brightening of the visual field generated by the build-up of rhythmic activity within the hippocampus.
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