Palinopsia revamped: A systematic review of the literature

Reversible bilateral central scotoma under scotopic conditions associated with oral semaglutide

Introduction

Semaglutide is a glucagon-like peptide-1 receptor agonist that treats type 2 diabetes mellitus and can be used as an adjunct for weight loss when combined with exercise and diet. Here we report a case of a bilateral, incongruent central visual scotoma under scotopic conditions in a board-certified ophthalmologist associated with semaglutide use that resolved quickly following medication discontinuation.

Case report

A 72-year-old male ophthalmologist (JAD) started 3.0 mg daily oral semaglutide (Rybelsus) to help with weight loss and seventeen days after treatment initiation developed a small, round central scotoma in his right eye that enlarged over several days. After two days a similar but smaller scotoma developed in his left eye. These symptoms were present only under scotopic conditions and were not visible in daylight or artificially lit conditions. When symptoms developed in the left eye, the medication was discontinued, and all symptoms completely resolved two days later. A subsequent clinical evaluation revealed no abnormalities on macular optical coherence tomography, fundus photography, fundus autofluorescence or Humphrey visual field.

Conclusions

This case of a bilateral central scotoma under scotopic conditions that resolved after medication discontinuation expands the knowledge of potential side effects from this increasingly popular diabetic and weight loss medication.

Alterations of the alpha rhythm in visual snow syndrome: a case-control study

BACKGROUND

Visual snow syndrome is a disorder characterized by the combination of typical perceptual disturbances. The clinical picture suggests an impairment of visual filtering mechanisms and might involve primary and secondary visual brain areas, as well as higher-order attentional networks. On the level of cortical oscillations, the alpha rhythm is a prominent EEG pattern that is involved in the prioritisation of visual information. It can be regarded as a correlate of inhibitory modulation within the visual network.

METHODS

Twenty-one patients with visual snow syndrome were compared to 21 controls matched for age, sex, and migraine. We analysed the resting-state alpha rhythm by identifying the individual alpha peak frequency using a Fast Fourier Transform and then calculating the power spectral density around the individual alpha peak (+/- 1 Hz). We anticipated a reduced power spectral density in the alpha band over the primary visual cortex in participants with visual snow syndrome.

RESULTS

There were no significant differences in the power spectral density in the alpha band over the occipital electrodes (O1 and O2), leading to the rejection of our primary hypothesis. However, the power spectral density in the alpha band was significantly reduced over temporal and parietal electrodes. There was also a trend towards increased individual alpha peak frequency in the subgroup of participants without comorbid migraine.

CONCLUSIONS

Our main finding was a decreased power spectral density in the alpha band over parietal and temporal brain regions corresponding to areas of the secondary visual cortex. These findings complement previous functional and structural imaging data at a electrophysiological level. They underscore the involvement of higher-order visual brain areas, and potentially reflect a disturbance in inhibitory top-down modulation. The alpha rhythm alterations might represent a novel target for specific neuromodulation.

TRIAL REGISTRATION

we preregistered the study before preprocessing and data analysis on the platform osf.org (DOI: https://doi.org/10.17605/OSF.IO/XPQHF , date of registration: November 19th 2022).

Visual imagery vividness correlates with afterimage conscious perception

Afterimages are illusory, visual conscious perceptions. A widely accepted theory is that afterimages are caused by retinal signaling that continues after the physical disappearance of a light stimulus. However, afterimages have been reported without preceding visual, sensory stimulation (e.g., conditioned afterimages and afterimages induced by illusory vision). These observations suggest the role of top-down, brain mechanisms in afterimage conscious perception. Therefore, some afterimages may share perceptual features with sensory-independent conscious perceptions (e.g., imagery, hallucinations, and dreams) that occur without bottom-up, sensory input. In the current investigation, we tested for a link between the vividness of visual imagery and afterimage conscious perception. Participants reported their vividness of visual imagery and perceived sharpness, contrast, and duration of negative afterimages. The afterimage perceptual features were acquired using perception matching paradigms that were validated on image stimuli. Relating these perceptual reports revealed that the vividness of visual imagery positively correlated with afterimage contrast and sharpness. These behavioral results support shared neural mechanisms between visual imagery and afterimages. This study encourages future research combining neurophysiology recording methods and afterimage paradigms to directly examine the neural mechanisms of afterimage conscious perception.

Visual Snow Syndrome in Patient with Migraine: Case Report and Literature Review

Visual snow syndrome (VSS) is a rarely diagnosed neurological phenomenon. It is a visual disorder characterised by the presence of numerous white, black, or translucent dots in the visual field, resembling the 'snow' of an analogue TV set experiencing reception interference. According to The International Classification of Headache Disorders, 3rd edition, visual snow is defined as a pattern of continuous small dots across the visual field lasting >3 months and accompanied by at least two of the following four additional symptoms: palinopsia, increased entoptic phenomena, photophobia, and nyctalopia. These complaints are not consistent with a typical migraine with visual aura and cannot be better explained by another disorder. The authors present the case of a 39-year-old woman who was diagnosed with VSS. The symptoms appeared after a migraine attack and had not alleviated. The patient reported a sensation of constant 'TV screen snow'. A neurological examination found no signs of focal damage to the nervous system. The results of the ophthalmological examination, MRI of the brain with contrast, MRI of the eye sockets, and EEG were normal. VSS is a phenomenon that is still not fully understood, different from migraine aura and associated with a number of additional symptoms. VSS is very difficult to treat. In this case, a lot of drugs were used without improvement. Further research must be conducted to determine the best treatment options for these patients.

Visual Snow: Updates and Narrative Review

PURPOSE OF REVIEW

Visual snow (VS) involves visualization of innumerable dots throughout the visual field, sometimes resembling "TV static." Patients who experience this symptom may also have additional visual symptoms (e.g., photophobia, palinopsia, floaters, and nyctalopia) with a pattern now defined as visual snow syndrome (VSS). This manuscript describes both VS and VSS in detail and provides an updated review on the clinical features, pathophysiology, and optimal management strategies for these symptoms.

RECENT FINDINGS

VS/VSS may be primary or secondary to a variety of etiologies, including ophthalmologic or brain disorders, systemic disease, and medication/hallucinogen exposure. Evaluation involves ruling out secondary causes and mimics of VS. Increasing evidence suggests that VSS is a widespread process extending beyond the visual system. Pathophysiology may involve cortical hyperexcitability or dysfunctional connectivity of thalamocortical or attention/salience networks. VSS is typically a benign, non-progressive syndrome and can be managed with non-medicine strategies. Though no medication provides complete relief, some may provide partial improvement in severity of VS.

Visual snow syndrome and migraine: a review

Visual snow syndrome is a neurological condition characterized by ongoing prominent phenomena described consistently as tiny dots moving across the entire visual field, often associated with complex visual symptoms. These can take the form of afterimages, entoptic phenomena, nyctalopia and light sensitivity. Although some of these symptoms can be benign, they can nonetheless become significantly impactful for many who experience them, particularly in cases that have a sudden and abrupt start. As visual snow syndrome becomes increasingly recognized in clinical practice we begin to learn about its typical presentation and underlying pathophysiology. Treatment of visual snow, however, still proves quite challenging, and efforts need to be focused on unravelling the biological mechanisms of the syndrome. This endeavour has characterized the most recent research on visual snow, mostly involving neuroimaging, neurophysiological and neurobehavioral studies aimed at understanding its underlying neural signature. Another important aspect of the syndrome, which will likely prove critical in deepening our understanding of visual snow, is represented by the intricate biological and historical connexion with migraine. This narrative review focused on visual snow syndrome will explore its clinical, pathophysiological and treatment aspects in detail.

Imprinting: expanding the extra-pharmacological model of psychedelic drug action to incorporate delayed influences of sets and settings

Background

Psychedelic drug experiences are shaped by current-moment contextual factors, commonly categorized as internal (set) and external (setting). Potential influences of past environments, however, have received little attention.

Aims

To investigate how previous environmental stimuli shaped the experiences of patients receiving ketamine for treatment-resistant depression (TRD), and develop the concept of "imprinting" to account for such time-lagged effects across diverse hallucinogenic drugs.

Methods

Recordings of treatment sessions and phenomenological interviews from 26 participants of a clinical trial investigating serial intravenous ketamine infusions for TRD, conducted from January 2021 to August 2022, were retrospectively reviewed. A broad literature search was undertaken to identify potentially underrecognized examples of imprinting with both serotonergic and atypical psychedelics, as well as analogous cognitive processes and neural mechanisms.

Results

In naturalistic single-subject experiments of a 28-year-old female and a 34-year-old male, subjective ketamine experiences were significantly altered by varying exposures to particular forms of digital media in the days preceding treatments. Higher levels of media exposure reduced the mystical/emotional qualities of subsequent psychedelic ketamine experiences, overpowering standard intention-setting practices and altering therapeutic outcomes. Qualitative data from 24 additional patients yielded eight further spontaneous reports of past environmental exposures manifesting as visual hallucinations during ketamine experiences. We identified similar examples of imprinting with diverse psychoactive drugs in past publications, including in the first-ever report of ketamine in human subjects, as well as analogous processes known to underly dreaming.

Conclusions/interpretation

Past environmental exposures can significantly influence the phenomenology and therapeutic outcomes of psychedelic experiences, yet are underrecognized and understudied. To facilitate future research, we propose expanding the contextual model of psychedelic drug actions to incorporate imprinting, a novel concept that may aid clinicians, patients, and researchers to better understand psychedelic drug effects.

Clinical trial registration

ClinicalTrials.gov, identifier NCT04701866.

Psychedelic replications in virtual reality and their potential as a therapeutic instrument: an open-label feasibility study

Background

Recent research has shown promising results for the therapeutic benefits of psychedelics. One popular view claims that these benefits are mediated by the subjective experiences induced by these substances. Based on this, we designed a virtual reality experience, Psyrreal, that mimics the phenomenological components of psychedelic experiences.

Aims

We aimed to investigate the therapeutic efficacy of Psyrreal and psychedelic VR experiences in treating depressive symptoms as well as explore the effect of Psyrreal on subjective factors which have been suggested to mediate the therapeutic benefits of psychedelics.

Methods

In this open-label feasibility study, thirteen participants with mild-to-moderate depression underwent a 2-day therapeutic intervention implementing Psyrreal. Depressive symptoms were evaluated by the Emotional State Questionnaire (EST-Q2) at the start of the intervention and 2 weeks after. A thematic analysis of semi-structured interviews after Psyrreal was also conducted as an additional assessment of the method.

Results

A 2-day intervention implementing Psyrreal led to significant decreases in depressive symptoms at the 2-week follow-up (n = 10, p = 0.007, Hedges' g = 1.046) measured by the Emotional State Questionnaire (EST-Q2). The analysis of semi-structured interviews suggests that Psyrreal could lead to insight and alterations in the sense of self in some people.

Conclusion

This work proposes a novel method using virtual reality to augment the treatment of psychological disorders as well as to precisely investigate the mediating subjective factors of the therapeutic effects of psychedelic substances. Our preliminary results suggest that VR experiences combined with psychological support show potential in treating depressive symptoms and further research into similar methods is warranted.

Short-term palinopsia after three doses of clomiphene: A case report

Palinopsia is a phenomenon consisting of the persistence or recurrence of a visual image after the stimulus has been removed, and can be static or kinetic. Palinopsia can be caused by a variety of different factors. Drug-induced palinopsia usually takes the form of visual trailing, a subset of illusory palinopsia, where patients report that an object leaves after-images trailing behind the object. There have been few reported cases of clomiphene-induced palinopsia. All have led to permanent palinopsia. This report demonstrates a case of transient clomiphene-induced palinopsia. Palinopsia occurred after only three doses of clomiphene and resolved within 10 days of cessation of therapy.

Differential Diagnosis of Visual Phenomena Associated with Migraine: Spotlight on Aura and Visual Snow Syndrome

Migraine is a severe and common primary headache disorder, characterized by pain as well as a plethora of non-painful symptoms. Among these, visual phenomena have long been known to be associated with migraine, to the point where they can constitute a hallmark of the disease itself. In this review we focus on two key visual disorders that are directly or indirectly connected to migraine: visual aura and visual snow syndrome (VSS). Visual aura is characterized by the transient presence of positive and negative visual symptoms, before, during or outside of a migraine attack. VSS is a novel stand-alone phenomenon which has been shown to be comorbid with migraine. We discuss key clinical features of the two disorders, including pathophysiological mechanisms, their differential diagnoses and best treatment practices. Our aim is to provide an aid for clinicians and researchers in recognizing these common visual phenomena, which can even appear simultaneously in patients with an underlying migraine biology.

Palinopsia

Palinopsia is an uncommon but important neuro-ophthalmic condition. It can present with a range of visual phenomena and may be misdiagnosed as migraine or a functional disorder. The list of possible causes is long and includes structural cerebral lesions. We present a clinical case to illustrate the condition before reviewing different palinoptic subtypes and discussing how these may help clinicians to narrow the differential diagnosis.

Cortical oscillatory dysrhythmias in visual snow syndrome: a magnetoencephalography study

Visual snow refers to the persistent visual experience of static in the whole visual field of both eyes. It is often reported by patients with migraine and co-occurs with conditions such as tinnitus and tremor. The underlying pathophysiology of the condition is poorly understood. Previously, we hypothesized that visual snow syndrome may be characterized by disruptions to rhythmical activity within the visual system. To test this, data from 18 patients diagnosed with visual snow syndrome, and 16 matched controls, were acquired using magnetoencephalography. Participants were presented with visual grating stimuli, known to elicit decreases in alpha-band (8–13 Hz) power and increases in gamma-band power (40–70 Hz). Data were mapped to source-space using a beamformer. Across both groups, decreased alpha power and increased gamma power localized to early visual cortex. Data from the primary visual cortex were compared between groups. No differences were found in either alpha or gamma peak frequency or the magnitude of alpha power, p > 0.05. However, compared with controls, our visual snow syndrome cohort displayed significantly increased primary visual cortex gamma power, p = 0.035. This new electromagnetic finding concurs with previous functional MRI and PET findings, suggesting that in visual snow syndrome, the visual cortex is hyperexcitable. The coupling of alpha-phase to gamma amplitude within the primary visual cortex was also quantified. Compared with controls, the visual snow syndrome group had significantly reduced alpha–gamma phase–amplitude coupling, p < 0.05, indicating a potential excitation–inhibition imbalance in visual snow syndrome, as well as a potential disruption to top-down ‘noise-cancellation’ mechanisms. Overall, these results suggest that rhythmical brain activity in the primary visual cortex is both hyperexcitable and disorganized in visual snow syndrome, consistent with this being a condition of thalamocortical dysrhythmia.

Perception of Happening: How the Brain Deals with the No-History Problem

In physics, the temporal dimension has units of infinitesimally brief duration. Given this, how is it possible to perceive things, such as motion, music, and vibrotactile stimulation, that involve extension across many units of time? To address this problem, it is proposed that there is what is termed an "information construct of happening" (ICOH), a simultaneous representation of recent, temporally differentiated perceptual information on the millisecond time scale. The main features of the ICOH are (i) time marking, semantic labeling of all information in the ICOH with ordinal temporal information and distance from what is informationally identified as the present moment, (ii) vector informational features that specify kind, direction, and rate of change for every feature in a percept, and (iii) connectives, information relating vector informational features at adjacent temporal locations in the ICOH. The ICOH integrates products of perceptual processing with recent historical information in sensory memory on the subsecond time scale. Perceptual information about happening in informational sensory memory is encoded in semantic form that preserves connected semantic trails of vector and timing information. The basic properties of the ICOH must be supported by a general and widespread timing mechanism that generates ordinal and interval timing information and it is suggested that state-dependent networks may suffice for that purpose. Happening, therefore, is perceived at a moment and is constituted by an information structure of connected recent historical information.

Palinopsia as an initial symptom of cerebral amyloid angiopathy-related inflammation

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We report the first case of cerebral amyloid angiopathy-related inflammation (CAA-RI) presenting palinopsia initially.

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Palinopsia is generally caused by intracranial diseases involving the parietal and occipital areas.

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CAA dominantly affects parietal and occipital lobes, therefore palinopsia could be an important phenomenon of the disease.

Visual Snow Syndrome as a Network Disorder: A Systematic Review

Aim: By reviewing the existing clinical studies about visual snow (VS) as a symptom or as part of visual snow syndrome (VSS), we aim at improving our understanding of VSS being a network disorder. Background: Patients with VSS suffer from a continuous visual disturbance resembling the view of a badly tuned analog television (i.e., VS) and other visual, as well as non-visual symptoms. These symptoms can persist over years and often strongly impact the quality of life. The exact prevalence is still unknown, but up to 2.2% of the population could be affected. Presently, there is no established treatment, and the underlying pathophysiology is unknown. In recent years, there have been several approaches to identify the brain areas involved and their interplay to explain the complex presentation. Methods: We collected the clinical and paraclinical evidence from the currently published original studies on VS and its syndrome by searching PubMed and Google Scholar for the term visual snow. We included original studies in English or German and excluded all reviews, case reports that did not add new information to the topic of this review, and articles that were not retrievable in PubMed or Google Scholar. We grouped the studies according to the methods that were used. Results: Fifty-three studies were found for this review. In VSS, the clinical spectrum includes additional visual disturbances such as excessive floaters, palinopsia, nyctalopia, photophobia, and entoptic phenomena. There is also an association with other perceptual and affective disorders as well as cognitive symptoms. The studies that have been included in this review demonstrate structural, functional, and metabolic alterations in the primary and/or secondary visual areas of the brain. Beyond that, results indicate a disruption in the pre-cortical visual pathways and large-scale networks including the default mode network and the salience network. Discussion: The combination of the clinical picture and widespread functional and structural alterations in visual and extra-visual areas indicates that the VSS is a network disorder. The involvement of pre-cortical visual structures and attentional networks might result in an impairment of "filtering" and prioritizing stimuli as top-down process with subsequent excessive activation of the visual cortices when exposed to irrelevant external and internal stimuli. Limitations of the existing literature are that not all authors used the ICHD-3 definition of the VSS. Some were referring to the symptom VS, and in many cases, the control groups were not matched for migraine or migraine aura.

Visual snow syndrome, the spectrum of perceptual disorders, and migraine as a common risk factor: A narrative review

OBJECTIVE

The aim of this narrative review is to explore the relationship between visual snow syndrome (VSS), migraine, and a group of other perceptual disorders.

BACKGROUND

VSS is characterized by visual snow and additional visual and nonvisual disturbances. The clinical picture suggests a hypersensitivity to internal and external stimuli. Imaging and electrophysiological findings indicate a hyperexcitability of the primary and secondary visual areas of the brain possibly due to an impairment of inhibitory feedback mechanisms. Migraine is the most frequent comorbidity. Epidemiological and clinical studies indicate that other perceptual disorders, such as tinnitus, fibromyalgia, and dizziness, are associated with VSS. Clinical overlaps and parallels in pathophysiology might exist in relation to migraine.

METHODS

We performed a PubMed and Google Scholar search with the following terms: visual snow syndrome, entoptic phenomenon, fibromyalgia, tinnitus, migraine, dizziness, persistent postural-perceptual dizziness (PPPD), comorbidities, symptoms, pathophysiology, thalamus, thalamocortical dysrhythmia, and salience network.

RESULTS

VSS, fibromyalgia, tinnitus, and PPPD share evidence of a central disturbance in the processing of different stimuli (visual, somatosensory/pain, acoustic, and vestibular) that might lead to hypersensitivity. Imaging and electrophysiological findings hint toward network disorders involving the sensory networks and other large-scale networks involved in the management of attention and emotional processing. There are clinical and epidemiological overlaps between these disorders. Similarly, migraine exhibits a multisensory hypersensitivity even in the interictal state with fluctuation during the migraine cycle. All the described perceptual disorders are associated with migraine suggesting that having migraine, that is, a disorder of sensory processing, is a common link.

CONCLUSION

VSS, PPPD, fibromyalgia, and chronic tinnitus might lie on a spectrum of perceptual disorders with similar pathophysiological mechanisms and the common risk factor migraine. Understanding the underlying network disturbances might give insights into how to improve these currently very difficult to treat conditions.

Short-Wave Sensitive ("Blue") Cone Activation Is an Aggravating Factor for Visual Snow Symptoms

Background and Purpose: Visual Snow (VS) is a disorder characterised by the subjective perception of black-and-white visual static. The aetiology of this condition is not known. In our previous work we suggested that there is a link between short-wave (S or “blue” cone) signals and severity of visual snow symptoms. Therefore we aimed to further characterise this potential link.

Methods: Patients (n = 22) with classic VS based on the diagnostic criteria and healthy controls (n = 12), underwent Intuitive Colorimetry (IC) testing (Cerium Visual Technologies). Twelve hue directions (expressed as angle in CIE 1976 LUV space relative to D65) were rated on a five-point scale from preferred (relieving, positive score) to non-preferred (exacerbating, negative score), and overall preferred and non-preferred angles were chosen.

Results: A non-preferred violet region near the tritanopic confusion line / S-cone axis (267 deg.) was strongly associated with exacerbation of VS symptoms (range 250–310 deg, mean 276 ± 16, n = 20, Rayleigh p < 0.001). Two subjects with non-preferred region > 90 deg from mean were considered as outliers. Median rank at hue angle 270 deg was significantly lower than at angle 90 (−1.5 vs. 0.0, p < 0.001, Wilcoxon non-parametric rank-sum test). Patients showed preference for one of two spectral regions which relieved VS symptoms: orange-yellow (range 50–110 deg., mean 79 ± 24, n = 14) and turquoise-blue (range (210–250 deg., mean 234 ± 27, n = 8).

Conclusion: Our results show that visual snow symptoms are exacerbated by colour modulation that selectively increased levels of S-cone excitation. Because S-cone signals travel on primordial brain pathways that regulate cortical rhythms (koniocellular pathways) we hypothesis that these pathways contribute to the pathogenesis of this disorder.

Illusions, hallucinations, and visual snow

Illusions and hallucinations are commonly encountered in both daily life and clinical practice. In this chapter, we review definitions and possible underlying mechanisms of these phenomena and then review what is known about specific conditions that are associated with them, including ophthalmic causes, migraine, epilepsy, Parkinson's disease, and schizophrenia. We then discuss specific syndromes including the Charles Bonnet syndrome, visual snow syndrome, Alice in Wonderland syndrome, and peduncular hallucinosis. The scientific study of illusions and hallucinations has contributed significantly to our understanding of how eye and brain process vision and contribute to perception. Important concepts are the distinction between topologic and hodologic mechanisms underlying hallucinations and the involvement of attentional networks. This chapter examines the various ways in which pathological illusions and hallucinations might arise in relation to the phenomenology and known pathology of the various conditions associated with them.

Dyskinetopsic Palinopsia: Palinopsia Accompanied by Moving Afterimages

Palinopsia refers to the abnormal persistence, or recurrence, of visual images after a visual stimulus has subsided. We describe here a case of palinopsia accompanied by a visual motion perception disorder as manifested by moving afterimages. A 71-year-old man presented to us after having experienced acute-onset, vivid, visual hallucinations for 1 week. A detailed history revealed that he was hallucinating multiple living and nonliving objects. He also complained of a persistence of afterimages, particularly in the left visual field. He reported that, on a few occasions, while sitting by the window in his room, he had seen a moving car on the road; immediately after the car had disappeared from his sight, he had then seen the same car moving backward at almost the same speed-as if the driver had applied the reverse gear. A neuropsychological assessment did not reveal any deficits in attention, language, or episodic memory. Visual field testing by confrontational perimetry suggested left hemianopia. An MRI of the brain revealed an arteriovenous malformation in the medial part of the right occipital lobe, affecting both the lingual gyrus and the inferior occipital gyrus. Palinopsia has generally been described in reference to static afterimages. In our case, not only was the afterimage that was perceived by the patient in motion, but the direction of the movement was also opposite to that of the actual object. We propose the term dyskinetopsic palinopsia, or simply motion-related palinopsia, for this particular condition.

Neuro-ophthalmologic Findings in Visual Snow Syndrome

Background and Purpose

The findings of ophthalmic examinations have not been systematically investigated in visual snow syndrome. This study reviewed the abnormal neuro-ophthalmologic findings in a patient cohort with symptoms of visual snow syndrome.

Methods

We retrospectively reviewed 28 patients who were referred for symptoms of visual snow to a tertiary referral hospital from November 2016 to October 2019. We defined the findings of best corrected visual acuity (BCVA), visual field testing, pupillary light reflex, contrast sensitivity, full-field and multifocal electroretinography, and optical coherence tomography.

Results

Twenty patients (71%) were finally diagnosed as visual snow syndrome. Their additional visual symptoms included illusionary palinopsia (61%), enhanced entoptic phenomenon (65%), disturbance of night vision (44%), and photophobia (65%). A history of migraine was identified in ten patients (50%). The mean BCVA was less than 0.1 logarithm of the minimum angle of resolution, and electrophysiology showed normal retinal function in all patients. Contrast sensitivity was decreased in two of the seven patients tested. Medical treatment was applied to five patients which all turned out to be ineffective. Among the eight patients who were excluded, one was diagnosed with rod-cone dystrophy and another with idiopathic intracranial hypertension.

Conclusions

Neuro-ophthalmologic findings are mostly normal in patients with visual snow syndrome. Retinal or neurological diseases must be excluded as possible causes of visual snow.

The perceived present: What is it, and what is it there for?

It is proposed that the perceived present is not a moment in time, but an information structure comprising an integrated set of products of perceptual processing. All information in the perceived present carries an informational time marker identifying it as "present". This marker is exclusive to information in the perceived present. There are other kinds of time markers, such as ordinality ("this stimulus occurred before that one") and duration ("this stimulus lasted for 50 ms"). These are different from the "present" time marker and may be attached to information regardless of whether it is in the perceived present or not. It is proposed that the perceived present is a very short-term and very high-capacity holding area for perceptual information. The maximum holding time for any given piece of information is ~100 ms: This is affected by the need to balance the value of informational persistence for further processing against the problem of obsolescence of the information. The main function of the perceived present is to facilitate access by other specialized, automatic processes.

Structural and functional footprint of visual snow syndrome

Patients with visual snow syndrome suffer from a continuous pan-field visual disturbance, additional visual symptoms, tinnitus, and non-perceptional symptoms. The pathophysiology of visual symptoms might involve dysfunctional visual cortex. So far, the extra-visual system has not been investigated. We aimed at identifying structural and functional correlates for visual and non-visual symptoms in visual snow syndrome. Patients were compared to age- and sex-matched controls using ¹⁸F-2-fluoro-2-deoxy-d-glucose PET (n = 20 per group) and voxel-based morphometry (n = 17 per group). Guided by the PET results, region of interest analysis was done in voxel-based morphometry to identify structural-functional correspondence. Grey matter volume was assessed globally. Patients had corresponding hypermetabolism and cortical volume increase in the extrastriate visual cortex at the junction of the right lingual and fusiform gyrus. There was hypometabolism in the right superior temporal gyrus and the left inferior parietal lobule. Patients had grey matter volume increases in the temporal and limbic lobes and decrease in the superior temporal gyrus. The corresponding structural and functional alterations emphasize the relevance of the visual association cortex for visual snow syndrome. The broad structural and functional footprint, however, confirms the clinical impression that the disorder extends beyond the visual system.

When Left is One and Right is Double: An Experimental Investigation of Visual Allesthesia after Right Parietal Damage

Illusory visual phenomena, such as palinopsia, polyopsia or allesthesia, are rare manifestations of posterior cortical damage. Symptoms are characterized by illusory perceptions, ranging from isolated stationary objects to scenes and moving persons. Such illusions may appear while the original object is still in view, or become manifest with a delay and last for minutes, hours or even days. Some authors have suggested a disinhibited cortical response underlying visual illusions, but experimental studies supporting this hypothesis are lacking. Here, we examined a rare patient who after focal right parietal injury consistently reported a second stimulus on the left when briefly shown a target in his right hemifield. The patient perceived the illusory stimulus as less intense, and therefore concluded that it must have a different shape than the original stimulus. A masking experiment revealed that the frequency of the illusion was inversely related to the visibility of the original stimulus, suggesting that it depended on early, feedforward visual processing. We propose that illusory perceptions reflect the interplay of two physiological processes: a fast and automatic activation of contralateral, homotopic visual cortex after unilateral stimulation, and the lack of top-down inhibition following damage to the posterior parietal cortex.

Palinopsia Accompanied with Migraine Attack After Having Occipital Brain Abscess

Palinopsia is defined as persistence of recurrent visual images after the stimulus has been removed. A 55-year-old male patient with long-standing migraine history developed brain abscess in the right occipital lobe. The patient developed episodes of palinopsia accompanied with migraine attack after healing of occipital lesion. The phenomenon cannot be sufficiently explained with single risk factor, although occipital lesion and migraine are both known to cause palinopsia. We speculated that migrainous brain is not always symptomatic but may drive cortex sensitive for second insult, such as occipital brain lesion. The predisposition may contribute to appearance of palinopsia.

Symptoms related to the visual system in migraine

Migraine is a common headache disorder characterized by often-severe headaches that may be preceded or accompanied by a variety of visual symptoms. Although a typical migraine aura is not difficult to diagnose, patients with migraine may report several other visual symptoms, such as prolonged or otherwise atypical auras, "visual blurring", "retinal migraine", "ophthalmoplegic migraine", photophobia, palinopsia, and "visual snow". Here, we provide a short overview of these symptoms and what is known about the relationship with migraine pathophysiology. For some symptoms, the association with migraine is still debated; for other symptoms, recent studies indicate that migraine mechanisms play a role.

Illusory palinopsias induced by in vitro fertilization treatment: a case report

Background

In the current era, in vitro fertilization, a type of assisted reproductive technology, has been commonly used for infertility management and gestational surrogacy. The techniques that are routinely used in in vitro fertilization include ovarian hyperstimulation to generate multiple eggs, preparation of the ova and sperm, and culture and selection of resultant embryos before transfer into a uterus. These steps increase the chances of successful pregnancy following in vitro fertilization treatment many-fold, especially in young women. Complications reported with in vitro fertilization treatment include multiple gestations, ovarian hyperstimulation syndrome, and birth defects while ocular side effects reported include retinal detachment and progression of keratoconus. We report a case of visual illusory palinopsia following in vitro fertilization treatment in a patient with unexplained infertility.

Case presentation

A 31-year-old Asian woman was administered in vitro fertilization treatment for her unexplained infertility. She complained of visually disturbing flashes in her peripheral vision during her pregnancy. She described these flashes as occurring usually in the morning hours or while walking, coming in sets of three to four, occurring five–six times a day and lasting for less than 5–10 minutes. Her flashes were not accompanied by other ocular symptoms such as pain, redness, photophobia, or decrease in vision. Her ocular examination was normal. Neuroimaging with magnetic resonance imaging revealed no pathology. A diagnosis of visual illusory palinopsia secondary to in vitro fertilization treatment was made.

Conclusion

Disturbing visual palinopsia and afterimages can occur following in vitro fertilization treatment for infertility due to increased estrogen levels. This rare ocular side effect caused by in vitro fertilization treatment is not reported in the literature to the best of our knowledge. Gynecologists and/or infertility experts should educate their patients regarding these possible ocular symptoms. Even ophthalmologists should be aware of this rare cause for visual palinopsia.

Palinopsia Following Acute Unilateral Partial Vestibular Deafferentation: A Case Report

Palinopsia is defined as the persistence or reappearance of images after cessation of the visual stimulus. One patient presented episodes of palinopsia after the functional loss of the 3 semicircular canals of the right ear while the otolithic function was preserved. None of classical causes was identified in this patient, intoxications, brain tumors, migraines, psychiatric disorders, etc. For a movement to be perceived as a single event, central processes of temporal integration are necessary to correct the shift between the rapid vestibular information, and the slow visual information. However, it has been shown on animal models that vestibular inputs are slower than normal in case of peripheral deafferentation limited to the canalar function with preservation of the otolithic function, which is the case in this patient. Therefore, we hypothesize that episodes of palinopsia he presents result from the fact that temporal integration processes do not take into account the slower than normal vestibular information due to the peripheral disorder and continue to slow it down. Thus, the patient keeps the visual image in memory until the late arrival of the vestibular information.

There's something in the air

A 20-year-old woman presented with bilateral constant positive visual phenomenon since she was 9 years old. The symptoms had been worsening and becoming more intrusive in the last 3 years. Recently she has also had a migrainous episode. All ophthalmic and neurological investigations were normal. Her symptoms met the diagnostic criteria for visual snow. The diagnosis was explained, and the patient was reassured. Ophthalmologists and neurologists need to be aware of this condition to avoid over investigation and worsening of patient anxiety.

Fundamental computational constraints on the time course of perception and action

A cognitive system faced with contingent events that cause rapid changes in sensory data may (i) incrementally incorporate new data into the ongoing perceptual and motor processing; or (ii) restart processing on each new event; or (iii) sample the data and hold onto the sample until its processing is complete, while disregarding any contingent changes. We offer a set of computational first-principles arguments for a hypothesis, according to which any system that contends with certain classes of perception and behavioral control tasks must include the sample-and-hold option (possibly alongside the other two, which may be useful in other tasks). This hypothesis has implications for understanding the dynamics of perception and action. In particular, a sample-and-hold channel necessarily processes sensory data on some kind of cycle (which does not imply precise periodicity). Further, being prepared to face the world at all times requires that the sampling that initiates each cycle be triggered by every significant action on part of the agent itself, such as saccades. We survey a range of evidence for the sample-and-hold functionality, touching upon diverse phenomena such as attentional blink and backward masking, the yoking of olfaction to respiration, thalamocortical interactions, and metastable brain dynamics in perception and consciousness.

Transient monocular blindness: Vascular causes and differential diagnoses

Transient monocular blindness is an acute episode of ischemic origin in which one eye has profound visual loss, followed by full recovery within one hour. Transient monocular blindness most often occurs in the setting of retinal ischemia secondary to carotid embolism, but other mechanisms have been reported, including thrombosis (most often in the setting of giant cell arteritis), hemodynamic disorders (secondary to severe carotid stenosis), or vasospasm. Transient monocular blindness is considered a transient ischemic attack originating in the carotid arteries, and must be managed the same as transient ischemic attack involving the brain, in order to prevent a subsequent stroke.

Is conscious perception a series of discrete temporal frames?

This paper reviews proposals that conscious perception consists, in whole or part, of successive discrete temporal frames on the sub-second time scale, each frame containing information registered as simultaneous or static. Although the idea of discrete frames in conscious perception cannot be regarded as falsified, there are many problems. Evidence does not consistently support any proposed duration or range of durations for frames. EEG waveforms provide evidence of periodicity in brain activity, but not necessarily in conscious perception. Temporal properties of perceptual processes are flexible in response to competing processing demands, which is hard to reconcile with the relative inflexibility of regular frames. There are also problems concerning the definition of frames, the need for informational connections between frames, the means by which boundaries between frames are established, and the apparent requirement for a storage buffer for information awaiting entry to the next frame.

Migraine with brainstem aura: Why not a cortical origin?

Background Migraine with brainstem aura is defined as a migraine with aura including at least two of the following symptoms: dysarthria, vertigo, tinnitus, hypacusis, diplopia, ataxia and/or decreased level of consciousness. Aim The aim of this study is to review data coming from clinical observations and functional mapping that support the role of the cerebral cortex in the initiation of brainstem aura symptoms. Results Vertigo can result from a vestibular cortex dysfunction, while tinnitus and hypacusis can originate within the auditory cortex. Diplopia can reflect a parieto-occipital involvement. Dysarthria can be caused by dysfunctions located in precentral gyri. Ataxia can reflect abnormal processing of vestibular, sensory, or visual inputs by the parietal lobe. Alteration of consciousness can be caused by abnormal neural activation within specific consciousness networks that include prefrontal and posterior parietal cortices. Conclusion Any symptom of so-called brainstem aura can originate within the cortex. Based on these data, we suggest that brainstem aura could have a cortical origin. This hypothesis would explain the co-occurrence of typical and brainstem aura during attacks and would fit with the theory of cortical spreading depression. We propose that migraine with brainstem aura should be classified as a typical migraine aura.

Clomiphene citrate-induced visual hallucinations: a case report

BACKGROUND

Polycystic ovary syndrome is a common cause of chronic anovulation and infertility in otherwise healthy fertile couples. Clomiphene citrate is used as a first-line ovulation induction therapy in patients with polycystic ovary syndrome. Clomiphene citrate can cause both systemic and ocular side effects. We report a rare side effect of illusory palinopsias in a patient with polycystic ovary syndrome treated with ovulation induction therapy with clomiphene citrate, and emphasize the need for gynecologists and their patients to be aware of this rare ocular side effect.

CASE PRESENTATION

A 30-year-old Asian woman complained of persistent visual afterimages following treatment with 100 mg clomiphene citrate for anovulation. Her symptoms started on the fourth day after commencing the treatment and would last for 5 to 10 minutes. Similar visual symptoms were noted during her second cycle of treatment with clomiphene citrate. The severity of her symptoms reduced following the stoppage of the medication; however, the symptoms have persisted for more than 1 year since she stopped taking the drug.

CONCLUSIONS

Clomiphene citrate can cause disturbing illusory palinopsias. These afterimages persist even after stopping the infertility medication. It is a side effect not frequently seen by gynecologists or ophthalmologists. Gynecologists should make their patients aware of this rare ocular side effect when their patients start treatment with clomiphene citrate for infertility.

Alice in Wonderland Syndrome: A Clinical and Pathophysiological Review

Alice in Wonderland Syndrome (AIWS) is a perceptual disorder, principally involving visual and somesthetic integration, firstly reported by Todd, on the literary suggestion of the strange experiences described by Lewis Carroll in Alice in Wonderland books. Symptoms may comprise among others aschematia and dysmetropsia. This syndrome has many different etiologies; however EBV infection is the most common cause in children, while migraine affects more commonly adults. Many data support a strict relationship between migraine and AIWS, which could be considered in many patients as an aura or a migraine equivalent, particularly in children. Nevertheless, AIWS seems to have anatomical correlates. According to neuroimaging, temporoparietal-occipital carrefour (TPO-C) is a key region for developing many of AIWS symptoms. The final part of this review aims to find the relationship between AIWS symptoms, presenting a pathophysiological model. In brief, AIWS symptoms depend on an alteration of TPO-C where visual-spatial and somatosensory information are integrated. Alterations in these brain regions may cause the cooccurrence of dysmetropsia and disorders of body schema. In our opinion, the association of other symptoms reported in literature could vary depending on different etiologies and the lack of clear diagnostic criteria.

Is palinopsia in migraineurs an enhanced physiological phenomenon?

Background

We report the occurrence of palinopsia in patients with migraine and its correlation with migraine characteristics, triggers and allodynia.

Methods

This study included 153 consecutive patients with migraine and recorded their clinical details, including allodynia and migraine triggers and characteristics. Palinopsia was evaluated in migraineurs and 101 controls by using a questionnaire and a novel method.

Results

According to the questionnaire assessment, 9.8% migraineurs had palinopsia. According to the novel method, 57.5% of migraineurs and 12% of controls had palinopsia. Migraineurs most frequently had palinopsia to red color (51.6%), followed by yellow (49.7%), blue (47.7%), green (46.4%) and the least to white (30.7%). A similar pattern with a lesser frequency was noted in controls. The duration of palinopsia was longer in migraineurs than in controls (32.68 ± 20.24 vs. 5.92 ± 4.55 seconds; p < 0.001). Migraineurs with palinopsia differed from those without in terms of noise as a migraine trigger ( p < 0.001) and allodynia as a migraine-associated phenomenon ( p = 0.03). In multivariable analysis, predictors of palinopsia were the frequency ( p = 0.003) and severity ( p = 0.04) of headache and the presence of headache during examination ( p = 0.0001).

Conclusion

Migraineurs had a pattern of palinopsia to different colors that was similar to the controls, but the palinopsia of migraineurs was more frequent and of longer duration, especially during headaches.

Visual processing in migraine

Background

Migraine is a common neurological condition that often involves differences in visual processing. These sensory processing differences provide important information about the underlying causes of the condition, and for the development of treatments.

Review of psychophysical literature

Psychophysical experiments have shown consistent impairments in contrast sensitivity, orientation acuity, and the perception of global form and motion. They have also established that the addition of task-irrelevant visual noise has a greater effect, and that surround suppression, masking and adaptation are all stronger in migraine.

Theoretical signal processing model

We propose utilising an established model of visual processing, based on signal processing theory, to account for the behavioural differences seen in migraine. This has the advantage of precision and clarity, and generating clear, falsifiable predictions.

Conclusion

Increased effects of noise and differences in excitation and inhibition can account for the differences in migraine visual perception. Consolidating existing research and creating a unified, defined theoretical account is needed to better understand the disorder.