Different kinds of meditation are practiced in many religions and cultures for the general wellbeing of an individual. However, meditation-related experiences and negative effects of meditation are not uncommon. Meditation-induced psychosis has been reported in the past.
Here, we present a case of a year-old male patient who developed acute and transient psychosis twice after meditation and discuss the role of meditation as a precipitating factor to psychosis. Meditation is generally used to denote various forms of mental exercises with techniques of concentration or contemplation [ 1 ]. It is a state between attention to an object and absorption within it [ 2 ]. Meditation is a technique in which an individual practices activity to achieve a mentally clear and emotionally calm and stable state.
This is done either by mindfulness or focusing on an object or thoughts [ 3 ]. In Vipassana meditation, the meditator observes his own thoughts and sensations in a motionless seated position and meditates for hours [ 4 ].
Meditation is regarded as a self-regulation approach to reduce the stress and manage the emotion [ 5 ]. Meditation has a significant role in chronic illness such as hypertension, insomnia, and chronic pain [ 6 ]. Meditation generally has a beneficial effect on mental illnesses such as anxiety disorder, mood disorder, substance use disorder, and suicidality [ 7 ].
However, a few reports suggest that meditation can have hazards. As reviewed by West et al. There is also evidence that meditation may even lead to psychosis or worsen it in some cases [ 9 ].
In , Morita was the first to describe psychotic symptoms related to meditation in superstitious people with low educational levels and considered the phenomena as a culture-specific disorder [ 10 ]. It has also been described as a culture-bound syndrome [ 11 ]. Here, we present a case from our tertiary care center with recurrence of psychosis after practicing meditation. There are some previous case reports of psychotic disorder having association with meditation, but it has been difficult to show cause effect relationship between the two.
This paper reports a case in which psychosis was precipitated by intensive meditation Vipassana twice with an attempt to show the temporal relation between psychosis and meditation. The case was a year-old married male of middle socioeconomic status, who worked as a part-time officer in a private office and was preparing for a government officer job.
He had a well-adjusted premorbid personality with culturally accepted religious views. There was no history of any medical problems, trauma, or substance use as well as no history of any psychiatric illness in the family. The patient presented to the emergency department ED with abnormal behaviour and difficulties to be at home because of suspiciousness, aggressive behaviour, and disturbed sleep for five days.
On further evaluation, the family members gave a history of similar symptoms nine years earlier following ten days of intensive Vipassana meditation. At that time, the patient had a history suggestive of delusions of persecution and reference, auditory hallucination 2 nd person commenting type, and decreased sleep.
His symptoms had completely remitted within one month of taking psychotropic medication, details of which is not known. On detailed evaluation of the current episode of the patient, family members revealed that apart from the episode nine years back, he never had any other such episodes. However, thinking no harm can occur after many years, the patient had gone for a day meditation program in the Vipassana meditation centre for a second time.
He had been practicing the same intensive meditation for 18 days as in the past prior to the onset of illness. In this Vipassana meditation, the patient along with other participants would practice meditation for about 18 hours a day, eat once a day, and sleep as little as possible, i. During the Vipassana meditation, he had to sit in squatting position with eyes closed taking natural breaths in the meditation hall, a quiet place.
He had to focus his full attention to his body movements and sensations. He should not communicate with anyone by any means throughout the stay, nor involve in any other activity apart from meditation. Everything was going smoothly until the 16 th day of intensive meditation, when the patient started saying people were looking at him and trying to harm him, even though no one noticed any such activity.
Since the patient was found self-muttering, aggressive towards other participants, and not meditating, he was sent home on the 18 th day. At home also, he repeatedly expressed of harm from other unknown people, was firm about it, and did not believe his friends and family when they told there was no such activity. While awake and in full consciousness, he also started expressing of hearing voices—with his both ears—clearly coming from the room next to. These voices were not heard by others.
The patient was restless and aggressive and frequently expressed that he could hear voices saying family members were trying to harm him. He accused his wife of having an extramarital affair with his brother in his absence. He tore her clothes and burnt them and verbally abused his wife if she enquired about doing so. He blamed his wife and other unknown people conspiring against him and wanting to kill him by poisoning his food. He threw the food when served and physically assaulted his wife claiming the food is poisoned.
The family members attempt to reassure him, explaining to him that none of his suspicions was true and that they did not hear any voices of harming him went in vain as the patient did not believe them.
Hallucinations of this sort include large mountains, rivers and streams, heavenly spirits, ghosts, and monsters. One can also hear different sorts of sounds. The most commonly encountered are those of ghosts, monsters, and heavenly spirits. In meditation, one is strongly advised against becoming afraid of these ghosts, monsters, and heavenly spirits, because fear can cause harm to the gallbladder, the kidneys, and the Qi. In serious cases, it can lead to mental disorders.
Why do people experience these hallucinations during meditation? From the perspective of eastern religions, there is in addition to our world another place where human spirits go after death. At the same time, it also is a kind of training for our heart-minds, as it helps us take a calm and undisturbed perspective on many things.
When I was at Wudang mountain I met an old woman who enjoyed meditation and religious culture. She did not have a teacher, but he had built a thatch hut for herself on the mountain.
We chose to use inductive content analysis, where categories are derived from the data, because this is the method that is recommended if there is little former knowledge about a phenomenon Elo and Kyngas, Because the varieties of meditation-related experiences have not been well documented in scientific literature, it was crucial that the interview content was driven by the subject, not the researcher. A total of min of audio recording were transcribed into pages and separated into separate units of analysis.
Within the transcripts, a new unit of analysis was created for each change in speaker, concept, or event, and each unit was allocated to a separate row in an excel spreadsheet Cavanagh, ; Graneheim and Lundman, ; Elo and Kyngas, Following the methodology of open coding, coders assign a tentative heading or category to each unit of analysis. They then read and code the transcript repeatedly until all aspects of the content are categorized.
As the coding structure evolved from the initial open coding, the research team met repeatedly to create and revise a list of standardized definitions for each type of experience with inclusion and exclusion criteria, supported by example texts MacQueen et al. To establish reliability for the codebook, an interview was chosen at random and was coded independently by each of the researchers. Exclusion criteria were metaphorical uses of light that were not directly linked with visual perception or that had ambiguous phenomenal quality cf.
Complex involuntary mental images involving objects, figures, and scenes that were not linked to a light-related experience were included in another category and therefore are not addressed in this paper.
Among these reports, the level of light of the meditation environment varied according to setting and time of day and was not intentionally manipulated. Practitioners who reported lights had been practicing within one or more Buddhist traditions for an average of 5. Our discussion begins by presenting a basic typology of meditation-induced light experiences based upon the data derived from the coded interviews from our subject pool.
Data from these first-person reports of meditation-induced light experiences are then compared to typologies of related phenomena derived from traditional Buddhist literary sources. The second main subsection discusses the neurobiology of light-related experiences according to scientific research on sensory deprivation, perceptual isolation, and clinical disorders of the visual system. We draw upon this literature both to posit the possible underlying mechanisms of meditation-induced light experiences and in order to suggest a novel interpretation of meditation that calls attention to its structural similarities with sensory deprivation and perceptual isolation.
We end our discussion with the implications of our findings for the scientific study and clinical application of meditation. Literature throughout the Therav da Buddhist tradition describes a particular mental phenomenon called a nimitta. The nimitta arises once a preliminary mastery of concentration has been established, and especially through developing concentration by focusing attention on the inhalation and exhalation of the breath Ledi Sayadaw, Although the particular mental image or form of the nimitta varies across practitioners and depends upon the object of concentration, the most common Buddhist meditation practice involves taking the breath as a primary object of attention.
A fifth century treatise entitled The Path of Purification Buddhaghosa, , p. One practitioner from our study also described a white light that appeared to be the size of moon as seen in the night sky. Extensive presentations of light-related signs of attainment can be found in the Buddhist tantras — a vast body of literature associated with ritual and contemplative practices that developed and flourished in India between the seventh and the eleventh century Samuel, Various tantras present the progressive sequence of mental images in different orders; Gyatso explains that this is due to the different techniques that can be used to induce the involuntary mental images.
The second class of light-related phenomena includes patterned and diffuse changes to the visual field, most commonly described as shimmering, pixelation, or brightening. This class of phenomena can be distinguished from the first class on account of not having a distinct and circumscribed shape, size, color, or spatial location.
Full et al. In addition to the shimmering and pixelation described above, six practitioners reported a homogenous brightening of the visual field.
Four other practitioners characterized the homogenous field of light as a mental image arising behind closed eyes. On account of this curtain of light, this practitioner reported being able to perceive memories and dream-like reveries as clearly as external objects. Two practitioners also reported a proprioceptive dimension to their meditation-induced light experience. As suggested above, reports of meditation-induced light phenomena can be found across Buddhist traditions, in both historical, textual accounts and among accounts from contemporary practitioners.
A survey of both historical and contemporary accounts reveals that there is no single, consistent interpretation of meditation-induced light experiences in Buddhist traditions. Some types of light may signal that a particular discipline such as concentration has reached a certain stage of development, whereas other lights may be the result of imbalanced practice.
Some interpret lights as a vehicle for investigating the constructed nature of phenomenal appearances; other light experiences are deemed unimportant side effects of meditation.
In the context of Therav da and Tantric Buddhism, meditation-induced light experiences are often deliberately sought as part of the method of transforming consciousness or are interpreted as a sign that such transformations have occurred. At that point, this involuntary light experience can then replace the breath or an external object as the new object of concentration Ledi Sayadaw, Similarly, in Tibetan traditions, the progressive sequence of signs that are thought to manifest on account of tantric practices, including both discrete lightforms and diffuse lights such as shimmering, are interpreted as positive signs that the clarity and luminosity of the mind is becoming apparent to the practitioner Gyatso, ; Sherab and Dongyal, However, similar typologies of light-related experiences are elsewhere treated as involuntary side effects of meditation.
Some Therav da Buddhist authors from contemporary Burmese lineages Nanarama, , p. Like the lights that arise in the context of the imperfections of insight, light-related nyams such as pixelation are to be left alone, and the practitioner is to proceed without becoming attached to them Wallace, According to other traditional interpretations, especially prominent in the Dzogchen tradition of Tibetan Buddhism, one of the objectives of advanced meditation practices is to stabilize the lightforms that arise and investigate them Chagme and Gyatrul, , p.
Such meditation-induced light experiences are not important in and of themselves; rather, they are valuable only insofar as they assist the practitioner in recognizing the way in which the mind constructs visual appearances and reifies them as external objects Wangyal, , pp. In this trajectory of practice, certain Buddhist meditation traditions utilize visual hallucinations as a means of gaining insight into the way in which perceptual experience of the phenomenal world is constructed, rather than given.
Some contemporary theories in cognitive science have characterized phenomenal consciousness as a process that simulates the relationship between the body and its environment e. As the following section will demonstrate, the neurobiology of visual hallucinations and veridical visual perceptions are closely related Ffytche et al.
Scientific studies of light-related experiences tend to classify such phenomena as visual hallucinations. This section presents findings from sensory deprivation, perceptual isolation, and disorders of the visual system. Sensory deprivation includes exposure to environments that present the subject with minimal sensory input. Sensory deprivation may include occlusion of individual sense organs, such as with earplugs or blindfolds, or multiple senses at once, such as through sitting alone in a dark and silent room.
Perceptual isolation refers to exposure to homogenous, invariant, or unstructured stimuli Wackermann et al. Among disorders of the visual system, Charles Bonnet Syndrome is classically associated with visual hallucinations and light-related experiences. Charles Bonnet Syndrome is most commonly found among elderly patients who have very poor vision or are blind on account of an impairment of their visual system, ranging from eye abnormalities to dysfunctions in the occipital lobe Vukicevic and Fitzmaurice, ; Kazui et al.
Hallucinations are different both from illusions, which are distortions of actual external stimuli, and from intentionally constructed mental imagery, which remains under volitional control and lacks perceptual vividness Reichert et al. Thus, our typologies of visual hallucinations will focus on those that arise during wake, as the phenomenology of waking visual hallucinations is the most congruent with the reports from participants in our study.
Researchers of sensory deprivation Zubek et al. Documented visual hallucinations range from simple forms or flashes of light or color to grid-like patterns to animated figures or scenes. Simple hallucinations often include circumscribed objects, patterns, and diffuse changes across the visual field. Patterned hallucinations may include regular, overlapping patterns tessellopsia like lattices, grids, and cobwebs, branching forms dendropsia like vines, ropes or roads, and zigzag patterns teichopsia.
Other patterns include the perception of visual snow or television-like static. Diffuse hallucinations include a brightening of the visual field, descriptions of mist or fog, shimmering, or bright sunsets Ffytche and Howard, ; Merabet et al. TABLE 2. Comparative typology of visual hallucinations and meditation-related light experiences.
Both circumscribed and diffuse simple visual hallucinations arise as result of sensory deprivation Zubek et al. The authors also point out that natural environments, such as a uniformly blue or cloudy sky, can function in a manner similar to intentionally constructed perceptual isolation environments p. Simple hallucinations are much more common than complex ones. Simple hallucinations can be evoked with very brief exposure to attenuated input, whereas complex hallucinations require more prolonged or more extensive sensory deprivation or perceptual isolation Wackermann et al.
Complex hallucinations are thought to draw upon many brain areas, including those involved in memory Collerton et al. More prolonged or extensive deprivation and brain changes may also begin to include cross-modal experiences where visual phenomena are experienced proprioceptively and incorporated into body schema and emotional meaning or value structures Ffytche et al.
Researchers have found that simple visual hallucinations are associated with activity in the occipital cortex, the primary visual-processing center of the brain Boroojerdi et al. Ffytche et al. This led the researchers to conclude that in terms of their neurobiology, visual hallucinations are more like ordinary perceptions than they are like visualized mental images.
Similarly, a perceptual isolation study Lloyd et al. Attenuation of sensory input reliably leads to hallucinations, even after a short time. Decreased sensory input leads to spontaneous firing and hallucinations through homeostatic plasticity — a set of feedback mechanisms that neuronal circuits use to maintain stable activity and firing rates close to a set point Desai, Homeostatic plasticity may include adjusting synaptic input strength synaptic homeostasis or changing the intrinsic excitability of the neuron intrinsic plasticity Turrigiano, When sensory inputs are attenuated or lost, the homeostatic plasticity mechanisms increase neuronal excitability and firing thresholds Boroojerdi et al.
In the case of sensory attenuation, homeostatic mechanisms often overcompensate to the point of generating spontaneous firing, which is experienced subjectively as hallucinations Schultz and Melzack, ; Burke, ; Maffei and Turrigiano, ; Reichert et al. A wide variety of conditions of sensory attenuation or monotony lead to increased cortical excitability, spontaneous firing, and hallucinations. Given that meditators are reporting visual hallucinations in the context of meditation, it is worth considering the sensory attenuating qualities of meditation practices.
While there are a variety of approaches to meditation, many practices incorporate structural components analogous to sensory deprivation and perceptual isolation, including sensory, social and kinesthetic deprivation, or invariance. The practice of meditation tends to be done in social isolation or in groups in which social interactions are minimized.
During a formal practice session, practitioners adopt a stable, seated posture. The locations for meditation practice also tend to be quiet environments removed from excessive auditory stimuli. Through dimly lit environments or through practicing with the eyes closed or open with a fixed gaze, visual stimuli are restricted.
It is important to note that even when meditation is not practiced within such sensory minimal environments, the practice of meditation functions in a manner analogous to perceptual isolation through restricting attention to monotonous or homogenous stimuli.
In practices that involve movement, the emphasis is on monotonous, repetitive movements, such as slow walking. In concentration practice on the breath, other kinesthetic, auditory, and visual stimuli are deselected in order to attend, again and again, to the repetition of inhalation and exhalation. Even when meditators practice with their eyes open, the gaze either remains unfocused and on the entirety of the visual field or is restricted to a single invariant object.
Thus, whether through practicing in environments with minimal sensory input, or through attending only to monotonous, repetitive stimuli, the context and function of meditation is similar to both sensory deprivation and perceptual isolation Table 3.
That advanced practitioners often deliberately choose to isolate themselves further by practicing in remote caves or in sensory deprivation environments demonstrates how Buddhist meditation traditions have recognized the importance of practicing within sensory minimal environments. Not surprisingly, discussions of meditation experiences in dark retreat closely resemble the typology of visual hallucinations discussed above.
Tenzin Wangyal Rinpoche, who undertook an extensive dark retreat when he was a young boy, reports both simple and complex visual hallucinations arising as a result of the prolonged sensory deprivation Wangyal, , , pp. Tibetan Buddhists also prescribe a shorter-term technique of fixing the gaze upon a cloudless sky as a means of inducing simple visual hallucinations Gyatso, As mentioned above, Wackermann et al.
TABLE 3. Comparison of sensory deprivation, perceptual isolation, and meditation. In addition to the structural aspects of meditation practices listed above, it is possible that the intense attentional engagement of Buddhist meditation practices also functions as a form of sensory deprivation.
The act of paying attention facilitates the processing of relevant stimuli while inhibiting irrelevant stimuli. The active processing of relevant stimuli is associated with increased fast frequency gamma oscillations and decreased slow frequencies i.
In contrast, suppression or inhibition of irrelevant stimuli is associated with the opposite pattern, decreased beta and gamma and increased alpha power or alpha synchronization in areas not related to the task Pfurtscheller and Lopes da Silva, ; Suffczynski et al. Alpha activity is also associated with decreases in fMRI BOLD signal and is thought to reflect the functional inhibition of neural activity in task-irrelevant areas Goldman et al.
For example, during visual tasks, information from non-visual e. Studies of spatial attention have shown decreases in alpha power in areas related to active processing of target locations but increases in alpha in areas related to non-target locations Thut et al.
Although most early research on attention focused on gamma activity in task-relevant areas and ignored alpha activity in task-irrelevant areas, it now appears that alpha inhibition is as important or more important than gamma facilitation.
Indeed, optimal task performance on a number of cognitive tasks, including selective and sustained attention, is determined by the extent of alpha activity in task-irrelevant areas rather than gamma in task-relevant areas Dockree et al. Various meditation practices, especially focused attention or concentration practice, involve selecting target or relevant stimuli and deselecting non-target or irrelevant stimuli.
Areas of the body that are related to the sensations of breathing or walking are a common target of focus in many forms of Buddhist meditation, and the ability to maintain focus on these target areas and inhibit distracting non-target stimuli is considered to be a hallmark of proficiency in focused attention forms of meditative practice.
Meditation-related increases in interoceptive accuracy to frequently attended targets Kerr et al. Thus, it could be argued that proficiency or expertise in focused attention as a result of meditation can be indexed by the degree of cortical inhibition.
However, the model in this paper suggests that inhibition of non-target sensory input can also result in a compensatory increase in neuronal excitability, which is often measured either by a decreased sensory threshold or by increased firing rates or spontaneous firings hallucinations.
In terms of decreased sensory thresholds, studies of Tibetan Shamatha MacLean et al. In terms of increased firing rates, long-term practitioners in both Therav da Vipassan Cahn et al. The reports of visual hallucinations from this paper suggest that visual areas of the occipital cortex have become hyperexcitable as a result of focused attention on non-visual target areas.
While it is still unknown if meditation-related light experiences are indeed caused by suppression of sensory input via alpha inhibition leading to compensatory disinhibition, this model is supported by perceptual isolation and sensory deprivation studies.
Visual hallucinations in perceptual isolation Wackermann et al. Although the relationship to a visual hallucination is unclear, Lo et al. This association fits with existing neurobiological models that suggest that hallucinations can be related to alpha inhibition Hayashi et al.
Together these data suggest that the attentional and structural components of meditation serve to attenuate sensory input, which activates homeostatic forms of neuroplasticity that lead to hyperexcitability, spontaneous firing, and hallucinations. The possibility of viewing meditation practice as a form of sensory deprivation has potentially profound implications. Current medical technologies are combining non-invasive brain stimulation techniques that alter neuronal excitability and enhance cortical plasticity with training protocols to enhance outcomes in neuropsychiatric patients, including dementia, pain, addiction, anxiety, and depression Nitsche et al.
In addition to improving symptoms, this enhanced neuroplasticity is also associated with improved learning, working memory, attention, and other cognitive improvements Guse et al. Similarly, the attenuation of sensory inputs increases neuronal excitability and facilitates a period of enhanced neuroplasticity Ffytche et al. Whether through brain stimulation or sensory attenuation, changes in neuronal excitability that accelerate neuroplasticity can be used to facilitate therapeutic changes beyond usual training protocols.
Since meditation training contains sensory attenuation components, it is possible that this form of cognitive training may have enhanced neuroplastic potential. Furthermore, the appearance of visual lights or other hallucinations could potentially serve as an indicator of a period of enhanced neuroplasticity, during which the ability to make a significant affective, perceptual, or cognitive shifts could be maximized.
However, the meditation-induced light experiences described in this paper suggest that meditation is a form of sensory attenuation that is capable of activating an enhanced period of neuroplasticity that may not occur in other forms of skill acquisition.
Visual hallucinations arising in the context of meditation practice may serve as indicators that homeostatic plasticity has been activated and that the brain may be more malleable to learning and change. While still highly speculative, this suggests that the sensory attenuation components of meditation may enhance its neuroplastic potential beyond other forms of skill acquisition.
Meditation researchers are also currently struggling with ways to measure meditative proficiency or expertise. Meditation-induced light experiences are worthy of further consideration and study as a potential indicator of meditative proficiency. Converging reports from our subjects, Buddhist textual sources, as well as multiple scientific research domains suggest that lights may, at least in some cases, be signs that the practitioner has attained a certain degree of concentration.
Proficiency in concentration could be determined by the degree to which a practitioner is able to inhibit irrelevant inputs from impinging on attention. Meditation-related light experiences may serve as a fairly consistent signpost of concentrative attainment across Buddhist traditions because such visual hallucinations tend to arise as a result of the attenuation of sensory input. In addition, because the spontaneous firings that generate visual hallucinations are associated with the activation of homeostatic plasticity, they may also herald entry into a time of enhanced learning, progress, and insight.
However, any traditional or well-known marker of progress potentially introduces demand characteristics. Further research that triangulates self-reports with both behavioral and neurobiological markers is necessary. While light-related experiences arising in the context of meditation are well documented in traditional contexts, they are largely unknown in clinical settings. In assessing meditators practicing outside of traditional contexts, it is important to carefully attend to the nuances of light-related discourses when evaluating whether lights are signs of positive changes or inconsequential side effects of meditation.
In traditional contexts, meditation-induced light experiences are frequently subject to scrutiny before they are attributed either positive or negative value. Without the traditional safeguards of a student-teacher relationship, the clinical application of meditation practices may be particularly susceptible to misinterpreting lights and other meditation experiences, since visual hallucinations are well-known indicators of both psychosis and vision system impairment.
It is important, therefore, not to uncritically pathologize these anomalous perceptual experiences. Light-related experiences are likely to be benign, but may cause distress to the practitioner if they are unexpected or accompanied by other psychological changes.
By empirically studying and documenting meditation-induced light experiences and describing them within their traditional Buddhist frameworks, we hope to help educate clinicians and meditation teachers about some of the common side effects of meditation in order to create more appropriate support structures for practitioners. The investigation of phenomena that has received little empirical attention requires inductive methods that are intended to be free of both assumptions and hypotheses.
Thus, our grounded-theory-based approach, which is appropriate for this stage of research, is both a strength and a limitation. As a limitation, by not asking participants if they had certain experiences, such as lights, the current report may have underestimated the actual prevalence of light-related meditation experiences.
This study has a number of other limitations. Demand characteristics and subject expectations are an inherent limitation of many types of studies, including nearly all intervention studies, meditation studies, and pharmacology studies. First, lights are not commonly described in American Buddhist meditation literature and are likely not well known to most American practitioners.
Participants in this study were deliberately recruited on the basis that the experiences they had with meditation were unexpected. In our sample, only one participant made an explicit association between their own experience and Buddhist theories about the significance of lights. It may seem plausible that the light-related experiences in our sample were just hypnagogic hallucinations that were caused by falling asleep and not by meditation practice.
We find it unlikely that sleep played a role in these experiences for several reasons. First, hypnagogic hallucinations are extremely common Ohayon et al.
Second, Buddhist meditation practice, especially among more-experienced practitioners, is associated with an increased alertness that is neurologically distinct from and resistant to sleepiness Britton et al. Third, as described previously, hypnagogic hallucinations are phenomenologically and neurologically different from waking hallucinations that arise in the context of sensory deprivation or perceptual isolation Cheyne et al. Finally, several of our subjects reported that their eyes were open during these experiences, and mentioned them in conjunction with concentration, never drowsiness or sleep.
Nevertheless, future studies of meditation-induced light experiences should include real-time measurements of brain activity to rule out this possibility. Now that some of the basic phenomenology of meditation-related light experiences has been described, we can begin to investigate follow-up questions in a hypothesis-driven experimental design that uses quantitative statistical analyses.
Future studies would benefit from investigating light-related experiences in larger sample of practitioners, with a range of practice types and durations, including secular, clinical meditation practices e. The hypothesized link between concentration and meditation-induced light experiences could be empirically investigated with neuropsychological tests of attention e.
Real-time neuroimaging concurrent with reports of light experiences may be able to determine neurological mechanisms as well as the possible relationship to hypnagogic hallucinations. Future studies should also make an effort to control for light exposure, both in terms of the ambient light in the environment, and in terms of whether the eyes are open or closed.
Changes in light exposure can result in compensatory changes in the retina dark adaptation that may also cause short-lived changes in visual experience Lamb and Pugh,
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