Altered states phenomena induced by visual flicker light stimulation

Flicker light stimulation can induce short-term alterations in consciousness including hallucinatory color perception and geometric patterns. In the study at hand, the subjective experiences during 3 Hz and 10 Hz stroboscopic light stimulation of the closed eyes were assessed. In a within-subjects design (N = 24), we applied the Positive and Negative Affect Schedule (mood state), time perception ratings, the Altered State of Consciousness Rating Scale, and the Phenomenology of Consciousness Inventory. Furthermore, we tested for effects of personality traits (NEO Five-Factor Inventory-2 and Tellegen Absorption Scale) on subjective experiences. Such systematic quantification improves replicability, facilitates comparisons between pharmacological and non-pharmacological techniques to induce altered states of consciousness, and is the prerequisite to study their underlying neuronal mechanisms. The resulting data showed that flicker light stimulation-induced states were characterized by vivid visual hallucinations of simple types, with effects strongest in the 10 Hz condition. Additionally, participants’ personality trait of Absorption scores highly correlated with the experienced alterations in consciousness. Our data demonstrate that flicker light stimulation is capable of inducing visual effects with an intensity rated to be similar in strength to effects induced by psychedelic substances and thereby support the investigation of potentially shared underlying neuronal mechanisms.

Quantification of Retinal Vessel Myogenic Constriction in Response to Blood Pressure Peaks: Implications for Flicker Light-Induced Dilatation

Background/AimsFlicker-light induced retinal vessel dilatation (FID), a marker of microvascular endothelial function, has been shown to be blunted in sedentary cardiovascular risk patients (SR) as well as healthy physically active individuals (HA). This study aimed to quantify the retinal myogenic response to blood pressure (BP) peaks and its effects on consecutive FID for differentiation of microvascular health.MethodsTen HA and eleven SR with a previously established restriction of arteriolar FID (aFID) (<2.2%) were invited in order to assess BP-induced myogenic constriction following a standardized handgrip task and a consecutive FID. BP was measured beat-to-beat.ResultsThe complete dataset of nine HA (3 female, mean age 65 years) and nine SR (5 female, mean age 61 years) individuals was analyzed. The central retinal arteriolar diameter equivalent (CRAE) was 183 ± 11 μm for HA and 176 ± 20 μm for SR. Initial baseline aFID was 1.6 ± 0.4% in HA and 1.6 ± 0.7% in SR. Systolic (p = 0.334) and diastolic (p = 0.245) BP increase following the handgrip task was in the range of 20–30% and comparable in both groups. BP increase was followed by a significantly higher arteriolar (−2.9 ± 1.3% vs. −1.3 ± 0.6%, p < 0.01) myogenic constriction in HA compared to SR. Moreover, in the consecutive assessment of FID directly after the BP-induced vessel constriction, aFID (4.1 ± 2.0% vs. 1.6 ± 0.9%, p < 0.01) was higher in HA compared to SR.ConclusionInitial baseline aFID was blunted in HA and SR. Retinal myogenic constriction was impaired in SR compared to HA. The consecutive aFID after BP-induced myogenic constriction recovered in HA but remained blunted in SR. Additional assessment of retinal myogenic constriction needs to be considered to improve CV risk stratification and reduce false-positive findings of endothelial dysfunction in otherwise healthy active individuals.Clinical Trial RegistrationClinicalTrials.gov: NCT03986892 (https://clinicaltrials.gov/ct2/show/NCT03986892).

Impaired retinal microvascular function predicts long-term adverse events in patients with cardiovascular disease

Aims Endothelial dysfunction is a precursor to the development of symptomatic atherosclerosis. Retinal microvascular reactivity to flicker light stimulation is a marker of endothelial function and can be quantified in vivo. We sought to determine whether retinal microvascular endothelial dysfunction predicts long-term major adverse cardiovascular events (MACE). Methods and results In a single-centre prospective observational study, patients with coronary artery disease (CAD) or cardiovascular risk factors underwent dynamic retinal vessel assessment in response to flicker light stimulation and were followed up for MACE. Retinal microvascular endothelial dysfunction was quantified by measuring maximum flicker light-induced retinal arteriolar dilatation (FI-RAD) and flicker light-induced retinal venular dilatation (FI-RVD). In total, 252 patients underwent dynamic retinal vessel assessment and 242 (96%) had long-term follow-up. Of the 242 patients, 88 (36%) developed MACE over a median period of 8.6 years (interquartile range 6.0–9.1). After adjustment for traditional risk factors, patients within the lowest quintile of FI-RAD had the highest risk of MACE [odds ratio (OR) 5.21; 95% confidence interval (CI) 1.78–15.28]. Patients with lower FI-RAD were also more likely to die (OR 2.09; 95% CI 1.00–4.40, per standard deviation decrease in FI-RAD). In Kaplan–Meier analysis, patients with FI-RAD responses below the cohort median of 1.4% exhibited reduced MACE-free survival (55.5 vs. 71.5%; log-rank P = 0.004). FI-RVD was not predictive of MACE. Conclusion Retinal arteriolar endothelial dysfunction is an independent predictor of MACE in patients with CAD or cardiovascular risk factors. Dynamic retinal vessel analysis may provide added benefit to traditional risk factors in stratifying patients at risk for cardiovascular events.

Altered states phenomena induced by visual flicker stimulation

Flicker light stimulation is a non-pharmacological method to induce short-term consciousness alterations, like hallucinatory perceptions of colors and geometric patterns. Recently, the subjective experiences elicited by different techniques to induce altered states of consciousness were investigated in a structured manner. Such systematic quantification improves replicability, allows comparisons between techniques, and is the prerequisite to study their underlying neuronal mechanisms. In a within-subjects repeated measures design (N = 24), we assessed the subjective experiences during 3 Hz and 10 Hz flicker light stimulation, by application of the Positive and Negative Affect Schedule (mood state), time perception ratings, the Altered State of Consciousness Rating Scale, and the Phenomenology of Consciousness Inventory. Furthermore, we tested for effects of personality traits (NEO Five-Factor Inventory-2 and Tellegen Absorption Scale) on subjective experiences. The data show that flicker light stimulation-induced states were especially characterized by vivid visual hallucinations of simple types, with stronger effects in the 10 Hz condition. Besides, we found high correlations between the extent of the subjectively experienced alterations in consciousness state with participants’ personality trait of Absorption. Our data demonstrate that flicker light stimulation can induce visual effects comparable to the effects induced by psychedelic substances and thereby motivates the investigation of potentially shared underlying neuronal mechanisms.

Psychophysics Study on LED Flicker Artefacts for Automotive Digital Mirror Replacement Systems

LED flicker artefacts, caused by unsynchronized irradiation from a pulse-width modulated LED light source captured by a digital camera sensor with discrete exposure times, place new requirements for both visual and machine vision systems. While latter need to capture relevant information from the light source only in a limited number of frames (e.g. a flickering traffic light), human vision is sensitive to illumination modulation in viewing applications, e.g. digital mirror replacement systems. In order to quantify flicker in viewing applications with KPIs related to human vision, we present a novel approach and results of a psychophysics study on the effect of LED flicker artefacts. Diverse real-world driving sequences have been captured with both mirror replacement cameras and a front viewing camera and potential flicker light sources have been masked manually. Synthetic flicker with adjustable parameters is then overlaid on these areas and the flickering sequences are presented to test persons in a driving environment. Feedback from the testers on flicker perception in different viewing areas, sizes and frequencies are collected and evaluated.

Serum Phosphate and Microvascular Function in a Population-Based Cohort

Background and objectivesHigher serum phosphate is associated with cardiovascular events and all-cause mortality. Explanations of this association have focused on large vessel calcification and stiffness. Studies suggest that a higher serum phosphate induces microvascular dysfunction, but relationships in humans with direct measures of microvascular function are lacking.Design, setting, participants, & measurementsWe performed a cross-sectional analysis of 3189 community-living participants that underwent skin capillaroscopy, laser-Doppler flowmetry, and flicker light–induced retinal vessel responses. We used linear regression to assess the association between serum phosphate and each microvascular outcome. The primary outcome was skin capillary recruitment during postocclusive peak reactive hyperemia by capillaroscopy. Secondary outcomes included capillary recruitment during venous congestion, heat-induced skin hyperemic response, flicker light–induced retinal arteriolar, and venular dilation.ResultsThe mean age of the cohort was 59±8 years, 48% were women, 7% had an eGFR <60 ml/min per 1.73 m2, and the mean serum phosphate concentration was 3.2±0.5 mg/dl. A 1 mg/dl higher serum phosphate was independently associated with a 5.0% lower postocclusive capillary recruitment (95% CI, −10.0% to −0.1%). Results were similar for capillary recruitment with venous congestion (−4.5%; 95% CI, −9.8% to 0.7%). A 1 mg/dl higher serum phosphate was also independently associated with a 0.23% lower retinal venular dilation in response to flicker light (95% CI, −0.44% to −0.02%). A higher serum phosphate was not associated with change in flicker light–induced retinal arteriolar dilation or heat-induced skin hyperemic response, however a higher serum phosphate was associated with a lower heat-induced skin hyperemic response among men (−149% [95% CI, −260 to −38] per 1 mg/dl higher serum phosphate) but not women (P interaction, 0.01).ConclusionsHigher serum phosphate concentrations, even within the normal range, are associated with microvascular dysfunction in community-living individuals.PodcastThis article contains a podcast at https://www.asn-online.org/media/podcast/CJASN/2019_09_20_CJN02610319.mp3