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AUTOHYPNOTIC INDUCTION OF SLEEPRHYTHMS GENERATES VISIONS OF LIGHT

WITH FORM-CONSTANT PATTERNS

Philip T. Nicholson and R. Paul Firnhaber

Visions of internally-generated lights without memory-basedcontent (‘phosphenes’) have played major roles in the founding of,and in the continuing revitalization of, most of the world’s majorreligious traditions (Bucke 1969 [1901]; Laski 1961; Underhill 1990[1930]; Arbman 1963, 1968, 1970). Autobiographical accounts bymystics in these traditions suggest that two types of phosphene imagesare particularly prominent during the early stages of contemplativemeditation, images of phosphene rings (annuli), and images ofamorphous expanding waves (see Table 1). In this paper, we willexamine similar phosphenes (see Figure 1) from ethnographic studiesof tribal cultures and studies of prehistoric rock art, present a detaileddescription of similar phosphenes observed by the authors, and showhow analysis of phosphene spatiotemporal characteristics in light ofnew research in the neuroscience of vision, sleep, and epilepsy nowmakes it possible to identify the specific brain mechanisms thatgenerate these phosphene patterns.

The brain mechanisms implicated in this analysis are thosethat govern the normal, nightly transition from waking consciousnessto the early stages of slow wave, non-rapid-eye-movement sleep(NREMS). Slow wave sleep is the classic example of thephysiological state of ‘parasympathetic dominance,’ which ischaracterized by (1) synchronous brain rhythms, (2) relaxed skeletalmuscles, and (3) high-amplitude activity in hippocampal-septalcircuits (Mandell 1980; Winkleman 1986, 1990, 1992). Thisphysiological state is the final common outcome produced by manydifferent kinds of trance induction rituals (Winkleman 1986). In thispaper, we show that parasympathetic dominance can be induced by asimple autohypnotic technique combining immobility, relaxation, aninternal orientation, an attitude of expectancy, and fixation of attentivefixation on the center of the visual field. These behaviors are alsolikely to be present during the early stages of hallucinogen rituals.

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Figure 1. Images of internally-generated sensations of light withabstract geometric shapes and no memory-based content (‘phospheneimages’) in ethnographic reports and prehistoric rock art studies. A.Concentric Annular Images: l. Four concentric annuli: South Africa(Lewis-Williams and Dowson 1988, Fig. 1); California (Patterson1998, p. 43; Benson and Sehgal, Fig. 9-10). 2. Four concentric annuliwith central dot: Australia (Halifax 1982, pp. 39, 70; Taylor 1988, pp.286-7; Lawlor 1991, pp. 46, 48-49, 108); Ireland (Herity 1974, Fig.

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37). 3. Single annulus with central dot: Columbia (Reichel-Dolmatoff1978, Plate 38); Alaska (Nelson 1899, as cited in Benson and Sehgal,Fig. 5); Siberia (Vastokas 1977, as cited in Benson and Sehgal, Fig. 2,p. 6). 4. More than 4 densely-packed concentric annuli, a ‘tunnel-like’image which may represent a stream of dark, fast-paced recedingannuli observed during the emergence of hypersynchronous CTCseizure (see text): Mexico (Siegel and Jarvik 1975, pp. 125, 139);Ireland (Herity 1974, Fig. 81); California (Benson and Sehgal, Fig. 6,p. 8). 5. Double spiral (included here because it, along with the singlespiral, may represent an illusory sensation of movement associated withthe ‘tunnel’ sequence of dark, fast-paced annuli rather than anindependently-generate image): Ireland (Herity 1974, Fig. 70;Dronfield 1996, Fig. 9); Mexico (Halifax 1987, p. 71; Schaefer, 1996,Fig. 31, p. 156). B. Amorphous Waves and Small-Particle Mists: 1.‘Navicular’ image of horizontal ‘nested’ arcs: Ireland (Herity 1974, Fig.78); South Africa (Lewis-Williams and Dowson 1988, Figures 1 – 4;Lewis-Williams 1995, p. 7). 2. Juxtaposition of 2 sets of nested arcs:Columbia (Reichel-Dolmatoff 1975, Plates 36, 39, 1978, Plate 23);South Africa (Lewis-Williams and Dowson 1988, Fig. 2). 3. Parallelwavy lines: South Africa (Lewis-Williams and Dowson 1988, Figures1-2); California (Whitley 1994, Fig. 1). 4. Clusters of tiny dots orcircles: Columbia (Reichel-Dolmatoff 1975, Plate 36); South Africa(Lewis-Williams and Dowson 1988, Figures 1-2; Ouzman 1998, Figure3.6., p. 38). C. Eye-Like (Iris and Pupil) Images: Set 1. Ireland(Herity 1974, Fig. 28, 36); California (Patterson 1998, Fig. 3). Set 2.Columbia (Reichel-Dolmatoff 1987, Plates 10-11). E. CompoundImages: 1. Annuli-to-waves: South Africa (Lewis-Williams andDowson 1988, Fig. 1). 2. Annuli-plus-waves: Ireland (Herity 1974,Fig. 37; Dronfield 1996, Fig. 9). 3. Waves-to-eye: Ireland (Herity1974, Fig. 37). 3. Annuli-to-eyes: California (Whitley 1998, Fig. 1).

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Table 1. Visions of Abstract Geometric Phosphenes(Annuli, Amorphous Waves, and ‘Eyes’) Reported by Mystics inthe World’s Major Religious Traditions (Adapted from Nicholson1996a)

HINDU AND BUDDHIST MYSTICS

“a perfectly round, beautiful deep-blue shape, of a size appropriateto the center of a mandala, as if exquisitely painted, of extreme clarity...”Tsong Khapa

“a luminous revolving disc, studded with lights...a lotus flower infull bloom...” Gopi Krishna

“The round stone enlarged before my inner vision until it becamethe cosmic spheres, ring within ring, zone after zone, all dowered withdivinity.” Paramahansa Yogananda

“both my eyes became centered together...When this happened, ablue light arose in my eyes....like a candle flame without a wick...in theajna [brow] chakra.” Muktananda

“Calm heavens of imperishable Light...continents of violetpeace....purple suns.” Aurobindo

“there arose in me, brethern, vision of things not taught unless theDivine Eye [caksus] opens: there arose in me knowledge, insight, wisdom,light.” Gotama the Buddha

HEBREW MYSTICS

“the appearance of the wheels...was like the gleaming of beryl; andthe four had the same form, their construction being something like awheel within a wheel” Ezekiel

“something like a dome, shining like crystal, spread out about theirheads....And above the dome, something like a throne, in appearance likesapphire...” Ezekiel

“he gazes into the flaming eyes of the Chayot, highly vibrating beingscomposed of pure energy, and the wheel-shaped Ofanim, winged eyesthat glitter...” Nehuniah ben Hakana

“like a round ladder.... a full sphere, rolling back and forth beforehim...bright blue.” Abulafia

“A glowing light...clear brilliance...A purple light that absorbs alllights....” Moses de Leon

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CHRISTIAN MYSTICS

“his own state at the time of prayer resembles that of asapphire...[clear as the] sky.” Evagrius

“descending like a bright cloud of mist...like a sun, round as a circle.”Simeon Neotheologos

“beheld with the mysterious eyes of my soul the light that neverchanges.” Augustine of Hippo

“saw something in the air near him. He did not understand the typeof thing, but in some ways it appeared to have the form of a serpent, withmany things that shone like eyes, although they were not eyes.” Ignatiusof Loyola

“the soul puts on...a green almilla [mantle worn on shoulders beneatharmor]... It has one hole through which the eyes may look upwards...”John of the Cross

“a round thing, about the size of a rixdaler, all bright and clear withlight like a crystal.” H. Hayen

“I saw a bright light, and in this light the figure of a man the color ofsapphire...blazing with a gentle glowing fire...the three were in onelight....” Hildegard von Bingen

“I saw the eyes...I do not know if I was asleep or awake...” Angelaof Foligno

“an extraordinary circle of gold light...pulsating against a deep violetbackground....There were always four or five....As soon as one wouldfade, another would appear...” Phillip St. Romain

MUSLIM MYSTICS

“lights [like] chandeliers....stars, moon, or the sun...” Sharafuddinal-Maneri

“its color is deep blue; it seems to be an upsurge, like...water from aspring.” Najmoddin Kobra

“visualize yourself lying at the bottom of a well and the well..inlively downward movement.” Najmoddin Kobra

“a light colored green is the...suprasensory uniting allsuprasensories.” Alaoddawleh Semnani

“the light rises in the Sky of the heart [like] one or several light-giving moons...” Najm Razi

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Annular and wave-like phosphenes in ethnographic studies

The motif of concentric annuli appears in the decorative andritual art of many different tribes and also at many different rock artsites (see Figure 1). Among aboriginal tribes in Australia, “men ofhigh degree” (Elkin 1974 [1945]) draw 4 to 5 concentric annuli tocreate ceremonial ground-paintings (ilbantera) that symbolize a sacredwaterhole through which the ancestors, and all living beings, enter ordepart the visible world. A similar motif appears in many differentkinds of aboriginal art. (See photos in Halifax 1982:39, 70; Taylor,P. 1988:287; Lawlor 1999:46, 48-9, 107-108). To depart the visibleworld for Dreamtime, aboriginal seers often rely on autohypnotictechniques: a man withdraws from the group, “. . . sitting down byhimself with his thoughts in order ‘to see’. He is gathering his thoughtsso that he can feel and hear. Perhaps he then lies down, getting into aspecial posture, so that he may ‘see’ when sleeping. . . . “ (Elkin1977:56).

A prerequisite for becoming a shaman among the IglulikEskimos of Alaska is learning how to generate an inner “illumination,”or angákoq, “a mysterious light which the shaman suddenly feels inhis body, inside his head, within the brain, an inexplicable searchlight,a luminous fire. . . . (Rasmussen 1930: 111).” Holtved (1967) notesthat the shaman “gets his visions sitting or lying in deep concentrationat the back of the sleeping platform, behind a curtain or covered witha skin. The drum is not used in this connection (p. 47).” Somemasks made by Eskimo shamans in Siberia to commemorate theirjourneys to the spirit world use a face-sized set of concentric circlesto depict spirits (tanghak). (See Nelson 1899: Plate 99; Ray 1967:6-9, 17; both cited in Benson and Sehgal 1987).

Similar kinds of annular phosphenes are observed during theearly stages of hallucinogen intoxication. In a discussion of the peyote-induced visions of the Huichol Indians of the high Sierra Madre rangein Mexico, Schaefer (1996) reports that “phosphenes induced bypsychotic chemicals appear in two stages,” and first to appear arethe colored, abstract images, called nieríka, that “serve as portals toother worlds. Many take the form of pulsating mandalas (p.156).”(See Schaefer, Fig. 31; Benson and Sehgal 1987, Fig. 3). In a study

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analyzing the frequency of particular kinds of geometric figures inHuichol peyote visions, Siegel and Jarvik (1975) found that 71% ofitems referred to “simple forms, colors, and movement patterns,”and the most frequently-mentioned geometric form was a ‘tunnel’(15/58, or 26%).

Reichel-Dolmatoff’s studies of the Tukano tribe of theAmazonian rain forest (1972, 1975, 1978, 1987, 1996) report that“after one or two cups of yajé [ayahuasca]” Tukanos see severaldifferent kinds of “luminous patterns:” (1) circular shapes, whichthey draw as a single annulus with a dot in the center or as a set of 3to 4 concentric annuli, (2) “wavy threads called dáriri with colorsranging from green to blue to violet,” which Tukanos draw as wavylines in parallel or as clusters of curvilinear arcs nested one inside theother; and (3) eye-like images (1996, p. 33). These phosphene motifsare often used to decorate the walls of their houses. (See Reichel-Dolmatoff 1978, e.g., pp. 12-13, 23, & 36; 1996:157-203, and Plates36-39; also Reichel-Dolmatoff 1987, Plates 10, 1). The same kindsof images observed during ayahuasca intoxication also appear “duringfleeting states of dissocation, daydreaming, hypnagogic states,isolation, sensory deprivation, or other situations of stress (1996:33).”Reichel-Dolmatoff found many similarities between his catalogue ofphosphene motifs in Tukano art and a taxonomy developed severaldecades earlier in a series of psychophysics experiments by MaxKnoll.

The Knollian taxonomy of 15 basic phosphene forms

Building on the work of early European psychophysicists, Knoll(1958) led several teams (Knoll and Kugler 1959; Knoll et al. 1962,1963; Kellogg et al. 1965) in designing a series of experiments to seeif phosphene phenomena could be reliably reproduced by electronicstimulation of the forehead. Using electrical pulses in the EEGfrequency range (0.5 cycles per second [Hertz] to 32 Hz), they foundthat some subjects saw abstract geometric phosphenes in addition tothe shapeless flickers observed by all, and that, in a few cases, theseimages were “frequency-specific,” that is, they could be reliably re-excited by the same stimulus administered after several months (see

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Knoll et al. 1962). Combining data obtained from 313 subjects whodescribed 520 phosphene images, they constructed a taxonomy of 15basic phosphene forms (Kellogg et al. 1965).

Following up on reports that mescaline generates ‘form-constant’ phosphene patterns (Klüver 1966 [1944]), Knoll et al. (1963)gave an hallucinogen, mescaline, psilocybin, or LSD, to a volunteersubject before electrical stimulation. They found that drug-inducedvisual effects build up gradually and eclipse the frequency-specificphosphene images, but frequency-specific patterns reappear once thedrug dissipates. They concluded that frequency-specific phosphenesmust be generated by some kind of “resonance mechanism” in thebrain, although they were unable to propose a candidate mechanism.The Knollian taxonomy provided the first experimentally-basedevidence that electrical stimulation of an intact brain can evokeabstract, geometric phosphenes of the sort described in theanthropological literature, and thus it became influential inanthropological circles, not least among prehistoric rock artspecialists.

Annular and wave-like images in prehistoric rock art

Images of concentric annuli, wavy lines, and eye-like formshave also been found at prehistoric rock art sites in widely-dispersedgeographic locations, ranging from Australia to South Africa tocontinental Europe, Ireland, and in the far western regions of theUnited States (see Figure 1). To explain why people in so manydifferent prehistoric cultures carved abstract geometric images similarin form, and to explain why some of these rock art images resembleimages described in contemporary ethnographic reports or in theKnollian taxonomy, Lewis-Williams and Dowson (1988, 1993) haveproposed a “neuropsychological model” of prehistoric rock artproduction and consumption. This theory, which has been elaboratedin many subsequent studies (Whitley 1994, 1998; Lewis-Williams1991, 1995a, b; Dronfeld 1996a, b; Clottes and Lewis-Williams 1998;Patterson 1998), claims that the “best-fit explanation” for how andwhy some abstract, geometric images appear at prehistoric rock artsites is that these images represent depictions of phosphene phenomena

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observed by shamans (or others) during ASCs. Theneuropsychological theory remains controversial (e.g., see Bednarik1990; Bahn 1997).

One way of advancing the debate about the origins of rock art,and, at the same time, extending what we know about the tranceinduction practices of contemporary shamans, is to search for newways to demonstrate that specific trance-induction behaviors activatespecific brain mechanisms which then generate specific kinds ofphosphenes. The Knollian taxonomy, while it remains a valuableresource, suffers a drawback common to all taxonomies, thatcatalogues are not explanations. In this paper, we suggest that it isnow possible to move beyond taxonomies by drawing on recentresearch in the neuroscience of vision, sleep, and epilepsy to identifycausal links between trance induction behaviors, specific types ofphosphene imagery, and the kinds of neuronal events that would haveto take place in order for those images to appear in the visual field.

Case history

The subject, a medical writer with no history of drug or alcoholabuse, no family or personal history of epileptic symptoms, and nosectarian affiliation, is one of the co-authors (PTN) of this article. Ingraduate school he learned how to hypnotize himself using acombination of “progressive muscle relaxation” (Jacobson 1938),silent self-cuing (e.g., “let yourself relax”) used in autogenic training(Schultz and Luthe 1969), and mental images of floating or drifting.This image-based approach did not generate phosphenes, but afterthe author attended a course, except that phosphene images began toappear spontaneously.

To induce phosphenes, the author lies on his back, closes hiseyes, takes slow, deep, rhythmic breaths, keeps his eyes convergedand slightly depressed, and keeps his attention fixated on the centerof the visual field. The eye convergence is sustained with enoughforcefulness to elicit a sensation of “fullness” or “pressure” in theeyeball, and the fixation of attention is forceful enough to evoke asensation of ‘locking in.’ The concentration of attention also producesauditory feedback, a characteristic tinnitis cerebri that seems part

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sound but also part vibration. This sensation, which originates insidethe lower rim of the skull at about the level of the ears and feels as ifit radiates upward on both sides, could be described as a “dull buzz.”(This sound/vibration can be generated by staring very intently at anobject situated just beyond the tips of the fingers of the extendedarm.) To keep his level of arousal low and his mental field free ofdistraction, the author maintains a passive, indifferent attitude,allowing potentially distracting stimuli to drift in and out ofconsciousness without trying to suppress them. During this state ofcalm, inward orientation in which attention is fixed on the visualfield, the author begins to see waves of brightly-colored phosphenethat follow the predictable sequence described below. A similarsequence appears spontaneously during the normal, drowsy transitionto sleep if the author fixates on the visual field (Nicholson 1996a, b).

On one occasion, while suffering from the circadiandisturbances of ‘jet lag’ and associated sleep loss (having slept only4 of the preceding 36 hours), the author attempted to put himself tosleep just before dawn using his familiar technique of autohypnosis.He was surprised to see the familiar phosphenes appear effortlesslyand with unusual intensity, then to see them give way to new types ofphosphene images he had never seen before, including a dark, ‘tunnel’-like image formed by an influx of dark, fast-paced annuli (Nicholson1999, 2002a, b).

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Figure 2. Phosphene images induced by autohypnosis orspontaneously during the normal, nightly transition to slow wave sleep.A. One 5-second cycle of a ‘receding annuli’ sequence. Initially theauthor sees a dark, barely-perceptible wave - a sensation of movement -that flows inward from the 360° perimeter of vision, then he sees abright yellowish-green phosphene annulus illuminate in the visual fieldat about 80° of isoeccentricity. The annulus continues to shrink in

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diameter at a constant rate, preserving its symmetry, and disappearsinto the center of vision at 4 seconds (as estimated by the author’scount of “1001 . . . 1002.”). This shrinking generates an illusion thatthe annulus is ‘receding’ in 3D space. A new annulus appears every 5seconds (0.2 Hz) until the sequence terminates automatically after atotal of 4 to 5 cycles. About halfway through the trajectory, the annulusappears to fill-in with a phosphene disk. (During the early years ofphosphene induction, the color of the fill-disk was a brighter, moreopaque green than the rest of the annulus, but after several years ofphosphene induction, the color of the fill-disk changed to dark blue.)B. One example of an amorphous expanding wave with a ‘mist-like’texture. The first row shows one of many different propagationpatterns of an amorphous wave of dark blue phosphene. (The shiftfrom a yellow-green color to dark blue occurred at the same time as theblue shift in the annulus fill-disk, noted above.) These wavesilluminate upon reaching 80° of isoeccentricity, like the annuli, andthey usually enter from either the right or the left perimeter, then sweepacross the visual field with both an expanding and enveloping motion.As the leading edge expands into areas of the visual field that have notyet illuminated, the trailing edge begins to dissipate, so that the cloudis simultaneously expanding and shrinking. (The author is not able totime these amorphous waves by counting as he does with the annuli,since the amorphous waves disappear at the slightest deviation ofattention; however, it “feels like” the waves complete their trajectoryand disappear into the centerpoint of the visual field in a time framethat is only marginally longer than the 4-second duration of theannuli.) C. Eye-like phosphene nodes. After a prolonged session ofphosphene induction, the amorphous expanding clouds often begin topersist longer in the visual field and also to develop a brighter, morefinely-grained, irridescent phosphene node at the center. The center ofthis bright central core keeps ebbing back, uncovering a dark, ‘pupil’-like area surrounded by the bright, ‘iris’-like ring, then filling back inwhen promontories of bright phosphene jut into the center. The brightcore is restored momentarily but then the center ebbs away and theprocess begins again. This image bears an uncanny resemblance to adisembodied ‘eye’. Finally, after prolonged observation of successiveamorphous waves that condense into ‘eye-like’ images, the phosphenemay condense even more to form a ‘star-like’ cluster of thin, flashing,phosphene filaments colored white and blue, a tiny dot at the center ofthe visual field that appears to be hovering at some distance from the

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viewer. D. Tunnels formed by an influx of many, dark, fast-movingannuli. These non-illuminating annuli stream into the visual field at arate of more than one per second (≥2 Hz), so that two or more annulican be seen in the visual field at the same time. This inward flowquickly eclipses the preceding star-like image. The dark wavesgenerate an illusion of movement through a 3-dimensional ‘tunnel’ (seetext). After only a few seconds, the flood of dark annuli stops abruptlyand is eclipsed by the next image. E. A radiating spray of phosphene‘flecks’. A spray of mist-like phosphenes interspersed with tiny ‘flecks’seems to radiate out toward the viewer following a conical trajectoryand to ‘strike’ at the forehead. During this spray, the author feltcompelled to arch his back, open his mouth, and pull his head backagainst the pillow. There were also tremors in the small muscles of theface and extremities. (Adapted from Nicholson 2001a.) Observations of phosphene images

The phosphene images that are usually observed during self- hypnosis (or during a normal, drowsy transition to NREMS) are illustrated in Figure 2 with descriptions in the legend. The two- dimensional, schematic drawings presented here are not exact renderings of these amorphous, ever-changing, ‘smoke-like’ lights, but they do capture the important spatiotemporal characteristics. The drawings show threshold images of ‘receding’ annuli (2A), images of amorphous expanding waves (2B), and a ‘tunnel’-like image formed by several dark, fast-paced annuli (2C). There are two important points to note when comparing these phosphene images: (1) the annular images, both the bright annuli and the dark annular bands, have relatively well-formed edges (i.e., a high signal-to-noise ratio) and symmetrical shapes, unlike the amorphous expanding waves, and, (2) the dark annuli enter the visual field at a rate of 2 or more per second (≥ 2.0 Hz), ten times faster than the illuminated annuli that enter at 5 second intervals (0.2 Hz).

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Synchronous spindle bursts at sleep onset generatereceding annuli

To explain how stage 2 NREMS generates phospheneepiphenomena, we need to review several new breakthoughs in theneuroscience of sleep that have produced a consensus scenario aboutthe basic mechanisms that support slow wave sleep (Steriade andMcCarley 1990; McCormick and Pape 1990; Steriade et al. 1993a,b; von Krosigk et al. 1993). In experiments using animal models ofhuman sleep, researchers have found that the transition from wakingto NREMS is governed by the complex interaction of three differentbrain rhythms that reverberate back and forth in the reciprocalneuronal projections that link cortex and thalamus, the cortico-thalamo-cortical (CTC) circuit. The transition to NREMS beginswith a drowsy waking state (‘stage 1’), a time when large populationsof cells begin to oscillate in synchrony with ‘cortical slow (<1 Hz)waves.’

The cortical slow rhythms, when referred to the thalamus, lowerthe polarization of thalamic cell membranes (i.e., ‘hyperpolarization’).The thalamic reticular nucleus (RTN), a thin sheet of GABAergicinhibitory cells that covers the lateral posterior thalamus, respondsby changing its firing patterns: instead of firing the single spikesassociated with processing sensory signals, it shifts to firing short, 1to 3 second bursts of 7 to10 Hz spikes that wax and wane like old-fashioned wool ‘spindles.’ These synchronous spindle bursts recurevery 3 to 10 seconds (0.3 - 0.1 Hz), and terminate automaticallyafter a volley of 4.78 ± 1.62 bursts, i.e., 3 to 5 bursts (Uchida et al.1994). The spindle bursts continue to hyperpolarize thalamic cellmembranes until a threshold point at which the RTN stops firingthese bursts. At the same time, the sensory relay cells in the thalamusbegin to fire calcium spikes timed to the pulse of the cortical slowwave. The interaction between the cortical slow wave and the thalamiccalcium spikes generates the ‘delta wave’ activity of NREMS stagethree.

The timing of RTN spindle bursts (0.1 to 0.3 Hz intervals)closely matches the timing of the phosphene receding annuli; in bothcases, a new signal appears every 5 seconds, an interval of 0.2 Hz.

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Also, receding annuli terminate automatically after a volley of 3 to 5cycles, just like RTN spindle bursts. There is, to our knowledge, noother brain rhythm that operates in the visual pathways that sharesthese same temporal characteristics. Therefore, based on timing alone,it seems likely that phosphene receding annuli are generated by RTNspindle bursts, but this hypothesis can be strengthened by showingthat the shape and trajectory of the receding annuli can also beexplained by reference to spindle wave activity.

The shape of receding annuli is a function of LGN anatomy

Light receptors in the retina send projections that terminate inthe lateral geniculate nucleus (LGN) of the thalamus. The retinalaxons form one-to-one synapses with the thalamocortical (TC)neurons that relay visual signals to targets in the primary visual cortex.As shown in Figure 3A, the LGN is composed of six thin sheets(laminae) folded over a central hilus. These drawings, adapted fromanatomical studies by Le Gros Clark (1940 - 41), Connolly and VanEssen (1984), and Malpelli and Baker (1975), show how the largestand most dorsal layer, lamina 6, can be removed, converted to a two-dimensional shape, and then fitted with a grid that shows where thelines of equidistance (isoeccentricity) in the retina, and thus in thevisual field, are represented by TC cells in lamina 6. Since eachLGN represents the contralateral half of the visual field, the perceptionof a unified visual field results from fusion of neural events takingplace in both LGNs.

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Figure 3. Neurophysiological origins of the annular images. A.The primate lateral geniculate nucleus (LGN) converted into a 2-dimensional, retinotopic map. These drawings at the top of the Figure3 show how a retinotopic map of the outer surface of the LGN wasconstructed, a map we then use to demonstrate how TC cell dischargescan generate a phosphene annulus. The first drawing shows the

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anterior surface of the dorsal lamina 6, adapted from an anatomicalstudy of the monkey LGN by Le Gros Clark (1940-41). The next twodrawings in row 1 illustrate how Connolly and Van Essen (1984)separated the dorsal lamina from the rest of the LGN, flattened it intotwo dimensions, then adjusted it to show which TC cells in lamina 6represented which areas of the retina (and thus which areas of thecontralateral visual field). The grid shown here maps lines ofequidistance (isoeccentricities) from the center of the retina that werecalculated based on data published earlier by Malpelli and Baker(1975). The most important point to notice is that the TC cellsrepresenting peripheral vision are located in the more ventral regionsof the lamina, while TC cells representing central vision are locatednearer the dorsal pole. B. Origins of the phosphene ‘receding annuli’.As described in the text, the spatiotemporal characteristics of thereceding annuli can be explained as visual epiphenomena initiated byspindle bursts moving ventrodorsally through the RTN network in arelatively thin, coherent spatial wave. As it passes, the spindle waveinhibits the axons of a narrow band of TC cells in the geniculate lamina6, generating a dark annulus which blocks relay of all other afferentvisual signals, including the random metabolic discharge of the retinalreceptors which is responsible for the normal ‘eigengrau’ background.In the wake of the spindle wave, when TC cells are released frominhibition, many fire rebound spikes. Since each LGN represents halfof the visual field, a wave of TC cell rebound spikes moving alonglamina 6 from the more ventral regions (representing peripheral vision)toward the dorsal pole (representing central vision) will register in thevisual cortices as a hemi-annulus that shrinks in diameter. Spindlewaves are fired simultaneously in both RTNs, so their passing willrelease simultaneous waves of TC cell rebound spikes in both LGNs; inthe visual field, this pairing of TC cell rebound spikes will generate twocomplementary (reverse-image) phosphene annuli with tips fused toform a single annulus that shrinks in diameter. C. Origins of the dark,fast-paced annuli. A different pattern of activation of the samemechanism described above can explain the appearance of the dark,fast-paced annuli. If the RTN were to fire spindle waves at a rate eˆ2.0 Hz, or ten times the normal rate of 0.2 Hz - as happens duringemergence of hypersynchronous SW complexes - then the rapidsuccession of waves of inhibition prevents TC cells from recoveringenough to fire rebound spikes before the next spindle wave inhibition.The author observed an influx of dark annuli arriving at intervals of

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more than two per second (eˆ 2.0 Hz) during the transition from astate of calm contemplation to a paroxysmal ecstatic trance, mentionedin the text. (For more detail, see Nicholson [2001a]). The sensation ofmoving through a dark ‘tunnel’ that has been described in near deathexperiences (Ring, 1985) might result from sudden onset ofhypersynchronous activity in CTC circuits that is triggered by thephysiological effects of trauma, particularly head injuries.

The ability of TC cells in the LGN to relay visual signals fromthe retina to the cortex depends on the TC cells ‘receiving permission’from RTN inhibitory neurons arrayed in a thin sheet along the outersurface of the posterior thalamus. When TC cell axons leave theLGN, they pass through the RTN matrix where they are interceptedby inhibitory synapses. When the RTN begins firing synchronousspindle bursts, this rhythmical activity blocks the flow of sensorysignals: the wave of excitation that constitutes the spindle burst movesup through the RTN matrix of inhibitory synapses on TC cells, itimposes a wave of inhibition on all of the TC cell axons. Once thewave passes, this inhibition is removed, at which point the TC cellsusually fire rebound spikes (Coulter 1997). The waves of reboundspikes generate the phosphene epiphenomenon of receding annuli, asshown in Figure 3B and described in the accompanying legend.

Given the centripetal trajectory of the phosphene annuli, weknow that the waves of inhibition/release must begin near the moreventral regions of the LGN (where the TC cells representing theperiphery of the visual field are located) and move toward the dorsalpole (where the TC cells represent the center of the visual field).This same mechanism can also explain the dark, fast-paced annuli,as shown in Figure 3C. If the RTN were driven by cortical influencesto fire spindle bursts at a rate of e” 2 Hz, an acceleration that does infact occur during hypersynchronous cortical seizures (see below),then there will not be enough time between successive waves of spindleinhibition for TC cells to recover and fire rebound spikes. The resultof these successive inhibitions is a stream of thin, dark, recedingannuli that enter the visual field at a hypersynchronous rate of e” 2Hz. This stream of dark annuli generates a sensation of ‘optic flow,’

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i.e., an illusion of motion through a dark, tunnel-like space (Steinmetzet al. 1987).

Delta wave activity of stage 3 NREMS generatesamorphous expanding waves

To explain why amorphous expanding phosphene waves followthe receding annuli, we now continue our exposition of the consensusscenario of NREMS generation. When the RTN spindle bursts ofstage 2 terminate automatically, TC cells start to fire calcium spikesin response to the pulse of the cortical slow (< 1 Hz) wave. Theinteraction of the synchronous cortical slow waves and TC cell calciumspikes generates a synchronous brain rhythm that is recorded in thescalp EEG as delta (0.5 - 4.0 Hz) wave activity, the hallmark ofNREMS stages 3 and 4. Since delta waves appear automaticallyafter the spindle bursts, it is reasonable to expect that the amorphousphosphenes will appear right after the receding annuli stop, and thisis indeed the case.

It is also reasonable to expect that the propagation patterns ofcortical slow waves will also reflect the patterns of TC cell discharges.Cortical slow waves are a type of “periodic spontaneous expandingwave” that can be observed in large networks of locally-connectedneurons. Maeda et al. (1995) report that periodic synchronizedexpanding waves (1) originate every 10 to 20 seconds, (2) appear atrandom locations, (3) are relatively slow, averaging 50 mm/second,and (4) spread with unpredictable, asymmetrical patterns, propagating“sequentially from electrode to electrode, as each local group ofneurons ‘charges up’ its neighboring, nonrefractory areas.” Similarcharacteristics are associated with the amorphous expandingphosphenes: (1) they originate at unpredictable locations, (2) moveslowly, remaining visible for several seconds, and (3) flow intocontiguous regions that have not yet been illuminated.

After prolonged induction of amorphous expanding waves, abrighter node of phosphene may appear at the center of the mist-likewave. The center of this brighter, central disk ebbs away, leaving a

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dark area, then fills back in, creating an image that resembles an eye-like iris surrounding a dark pupil (see Figures 1 and 2).

Hypersynchronous cortical seizures generate the ‘tunnel’and ‘spray’ images

Research in animal models shows that the cellular mechanismsthat govern a normal transition to NREMS can be destabilized, givingrise to the spontaneous emergence of hypersynchronous seizures atsleep onset (Steriade and Contreras 1995; Contreras and Steriade1995; Lytton et al., 1997; Steriade and Contreras, 1998; Steriade etal, 1998; Necklemann et al, 1998; Timofeev et al. 1998). For this tohappen, cortical cells must already be abnormally excitable at thetime the transition to NREMS begins. During the emergence of ahypersynchronous seizure, there can be two kinds of paroxysmaldischarges: (1) cortical cells firing hypersynchronous spike-wave(SW) complexes at 1.5 to 2 Hz intervals, which causes thalamicRTN cells to fire spindle bursts at the same rate, or (2) cortical cellsfiring ‘fast runs’ of 10 to 15 Hz spike bursts, which causes TC cellsto discharge in an expanding wave with the unusual features describedbelow.

Based on this research, the phosphene image of a ‘tunnel’formed by dark receding annuli can be explained by cortical SWcomplexes at e” 2 Hz intervals driving RTN cells to fire spindle burstsat e” 2 Hz intervals, ten times faster than the normal rate of 0.2 Hz.These annuli are dark waves because spindle bursts driven at thisaccelerated rate impose successive waves of inhibition that do notallow time for TC cells to fire rebound spikes. The shift from astream of dark annuli to a radiating spray of phosphene flecks signalsthat cortical cells have shifted from firing SW complexes to firingfast runs. The spatial propagation pattern of cortical fast runs formsan “expanding epileptic penumbra,” i.e., waves of cortical celldischarges ‘rippling’ out in all directions from the epicenter of theseizure (Lytton et al. 1997; Steriade and Contreras 1998). This flowgenerates an epiphenomenal phosphene image of a ‘spray’ that seemsto ‘radiate’ outward toward the viewer. The variegated ‘texture’ of

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the radiating spray, its ‘fleck-like’ composition, is also consistentwith cortical fast run activity that drives TC cells to fire independently(Timofeev et al. 1998), generating a ‘mist-like’ phosphene spray with‘flecks’ that appear when groups of contiguous cells fire together.The researchers were “surprised by the high incidence of seizuresthat occurred spontaneously” at sleep onset in the cats they werestudying, and they suggested “the possibility that many spontaneouselectrographic seizures in ‘normal’ ([human) subjects areunrecognized, and that those sleeping individuals pass in and out ofseizures during their slow sleep oscillation . . . (Steriade et al.1998:1476).” Interestingly, Persinger (1984) found that SWcomplexes appeared in the EEG of a woman who was practicingglossolalia and “feeling a sense of unity with the cosmos.”

Conclusion

Sets of ring-like shapes (e.g., 3 to 5 annuli in close proximityor in concentric sets) that appear in indigenous art known to be relatedto ASCs can be explained as static, 2-dimensional representations oftemporal sequences of phosphene images of ‘receding annuli’generated by autohypnotic induction of thalamic spindle bursts thatsignal the onset of stage 2 NREMS. Similarly, wave-like or eye-likemotifs can be explained as representations of phosphene ‘amorphousexpanding waves’ generated by delta waves associated with stage 3or 4 NREMS. The inference of a sleep rhythm etiology is strengthenedif the two types of motifs are combined to form a single image, sincethis implies that the two types of images appear in tandem, like thedelta waves that follow spindle bursts during the transition to NREMS.Since these phosphenes represent ‘entry-level’ trance states, theiriconic representations might serve as symbols of the transition betweenordinary and non-ordinary realities. Sets of concentric annuli withmore than 5 rings can be explained as static, 2-dimensionalrepresentations of the ‘tunnel-like’ stream of dark, receding annuligenerated by SW complexes that emerge during hypersynchronousseizures. Images of ‘spirals’ might be seen as representations of howit feels to have the attention drawn into a tunnel of dark annuli ratherthan presenting a discrete type of phosphene image.

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