Biology subjects

Najjar, R. P.

Publications and source records attributed to Najjar, R. P..

9 recordsLinked to original sources

bioRxiv2026

Pre-task light exposure primes higher-order cognition and preserves mood

Light is a fundamental regulator of human physiology and behaviour. Whether prior light exposure shapes subsequent higher-order cognition and mood beyond the period of exposure remains unknown. We tested this in a within-subject, randomised crossover experiment in which 24 healthy young adult males completed a multimodal cognitive battery following 2x15 min of full-spectrum light (FL; median 1,029 melanopic equivalent daylight illuminance [mEDI]) or standard indoor light (SL; median 234 mEDI), with all testing conducted under identical dim illumination. FL improved Digit-Symbol Substitution Test accuracy and promoted digit-directed gaze reallocation, consistent with more efficient associative encoding. On the Balloon Analogue Risk Task, FL reduced reward-seeking behaviour and suppressed backward-referencing gaze transitions linking current and prior-trial reward information. Mood declined following SL but remained stable after FL. Sustained attention, vigilance, and subjective sleepiness were unaffected. Our findings identify pre-task FL exposure as a selective primer of higher-order cognition and mood, independent of alertness.

neuroscience↗

bioRxiv2026

Human-Perception-Aligned Machine Learning for Indoor-Outdoor Classification

Daylight is vital for eye, brain, and overall health, yet misperceptions of what constitutes true outdoor daylight exposure can lead to poor behavioural choices and weaken public health recommendations. We developed InNOut, a perception-aligned machine learning model trained on 73,879 minutes of multispectral light data to classify environments as indoor or outdoor, and benchmarked against public (n = 383) and expert (n = 17) judgments across 183 scenes. InNOut achieved excellent performance (AUC = 0.92 [95% CI, 0.92-0.93], sensitivity 73.9%, specificity 94.5%), closely aligning with expert (83.5%) and public (80.8%) judgments. Clear outdoor and indoor scenes were reliably classified, whereas ambiguous settings (e.g., windowed rooms, vehicles) were often judged indoor by participants but outdoor by the model, consistent with their spectral light profiles. InNOut bridges perception and measurement, offering a scalable means to map light environments and inform digital interventions in medicine and public health.

physiology↗

bioRxiv2024

Interactions between high-intensity light and unrestricted vision in the drive for hyperopia

PURPOSETo evaluate the impact of optical versus illuminance factors and their duration-dependency on lens-induced hyperopia (LIH) in chick eyes. METHODSHyperopia was induced in one eye in chicks (10 groups, n=126) from day 1 (D1) post-hatching until D8 using +10 D lenses with fellow eyes as controls. One group (LIH) served as the control without any interventions. Remaining groups were exposed to 2, 4 or 6 hours of unrestricted vision (UnV), high intensity light (HL), or both (HL +UnV). Ocular axial length (AL), refractive error, and choroidal thickness were measured on days 1, 4, and 8. Inter-ocular difference (IOD = experimental - contralateral eye) {+/-} SEM was used to express outcome measures. RESULTSBy D8, LIH decreased AL (-0.42{+/-}0.03 mm) and produced hyperopic refraction (+3.48{+/-}0.32 D) and choroidal thickening (+85.81{+/-}35.23 {micro}m) in the LIH group (all, P<0.001). Exposure to UnV reduced LIH (i.e., hyperopic refraction, axial shortening, and choroidal thickening) in a duration-dependent manner, whereas HL potentiated the development of LIH in a duration-dependent manner. When combined, UnV overpowered HL, with resultant impact on refraction and AL being close to UnV alone, except after 6 hours, when HL+UnV induced shorter AL compared to UnV alone (P=0.03). CONCLUSIONDaily exposure to HL, UnV, and HL+UnV altered LIH in a duration-dependent manner with UnV and LIH producing competing signals. The signal generated by UnV was generally stronger than HL in combined exposure, yet longer durations of HL affected the drive for emmetropization in eyes with UnV.

developmental biology↗

bioRxiv2023

Differences in the Pupillary Responses to Evening Light between Children and Adolescents

PurposeTo assess differences in the pupillary light responses (PLRs) to blue and red evening lights between children and adolescents. MethodsForty healthy participants (8-9 years, n=21; 15-16 years, n=19) completed a PLR assessment 1 h before their habitual bedtime. After a 1 h dim-light adaptation period (<1 lux), baseline pupil diameter was measured in darkness for 30 s, followed by a 10 s exposure to 3.0x1013 photons/cm2/s of either red (627 nm) or blue (459 nm) light, and a 40 s recovery in darkness to assess pupillary re-dilation. Subsequently, participants underwent 7 min of dim-light re-adaptation followed by an exposure to the other light condition. Lights were counterbalanced across participants. ResultsAcross both age groups, maximum pupil constriction was significantly greater (p< 0.001, {eta}p2=0.48) and more sustained (p< 0.001, {eta}p2=0.41) during exposure to blue compared to red light. For adolescents, the post-illumination pupillary response (PIPR), a hallmark of melanopsin function, was larger after blue compared with red light (p= 0.02, d=0.60). This difference was not observed in children. Across light exposures, children had larger phasic (p< 0.01, {eta}p2=0.20) and maximal (p< 0.01, {eta}p2=0.22) pupil constrictions compared to adolescents. ConclusionsBlue light elicited a greater and more sustained pupillary response than red light across participants. However, the overall amplitude of the rod/cone-driven phasic response was greater in children than in adolescents. Our findings using the PLR highlight a higher sensitivity to evening light in children compared to adolescents, and continued maturation of the human non-visual photoreception/system throughout development.

physiology↗

bioRxiv2023

Melatonin suppression by light involves different retinal photoreceptors in young and older adults

IntroductionAge-related sleep and circadian rhythm disturbances may be due to altered non-visual photoreception. Here, we investigated the temporal dynamics of light-induced melatonin suppression in young and older individuals. MethodsIn a within-subject design study, young and older participants were exposed for 60 minutes (0030-0130 at night) to 9 narrow-band lights (range: 420 to 620 nm). Plasma melatonin suppression was calculated at 15, 30, 45, and 60 min time intervals. Individual spectral sensitivity of melatonin suppression and photoreceptor contribution were predicted for each interval and age group. ResultsIn young participants, melanopsin solely drove melatonin suppression at all time intervals, with an invariant peak sensitivity at [~]485 nm established only after 15 minutes of light exposure. Conversely, in older participants, spectral light-driven melatonin suppression was best explained by a model combining melanopsin + L-cones with a stable peak sensitivity ([~]499 nm) at 30, 45, and 60 minutes of light exposure. ConclusionAging is associated with a distinct photoreceptor contribution to melatonin suppression by light. While in young adults melanopsin-only photoreception is a reliable predictor of melatonin suppression, in older individuals this process is jointly driven by melanopsin and L-cones. These findings offer new prospects for customizing light therapy for older individuals.

neuroscience↗

bioRxiv2023

ENLIGHT Consensus Checklist and Guidelines for reporting laboratory studies on the non-visual effects of light in humans

Beyond vision, light has wide-reaching effects on human health and well-being. However, there is no consensus on reporting light characteristics in studies investigating non-visual responses to light. This project aimed at developing a reporting checklist for laboratory-based investigations on the impact of light on non-visual physiology. To this end, a four-step modified Delphi process (three questionnaire-based feedback rounds and one face-to-face group discussion) involving international experts was conducted. Across these four rounds, an initial list of 61 items related to reporting light-based interventions was condensed to a final checklist containing 25 items, based upon consensus among experts (final n=60). Nine of these items were determined to be necessary to report regardless of the specific research question or context. A description of each item was provided in the accompanying guidelines. Most participants (92%) reported being satisfied or very satisfied with the consensus process, checklist, and guidelines. The ENLIGHT Checklist and Guidelines are the first consensus-based guidelines for documenting and reporting ocular light-based interventions for human studies. The implementation of the checklist and guidelines will enhance the impact of light-based research by ensuring comprehensive documentation and reproducibility and enabling data aggregation across studies.

neuroscience↗

bioRxiv2022

A duration-dependent interaction between high-intensity light and optical refocus in the drive for myopia control

PURPOSETo evaluate the duration-dependent and synergetic impact of high-intensity light (HL) and optical refocus (RF) on lens-induced myopia (LIM) development in chickens. METHODSMyopia was induced in one eye in chicks (10 groups, n=126) from day 1 post- hatching (D1) until D8 using -10D lenses. Fellow eyes remained uncovered as controls. Nine groups were exposed daily to continuous 2 hours (h), 4h, or 6h of either HL (15,000 lux); RF (removal of -10D lens); or both (HL+RF). One group served as the LIM group without any interventions. Ocular axial length (AL), refractive error, and choroidal thickness were measured on D1, D4, and D8. Outcome measures are expressed as inter-ocular difference (IOD= experimental - control eye) {+/-}SEM. RESULTSBy D8, LIM increased AL (0.36{+/-}0.04 mm), myopic refraction (-9.02{+/-}0.37D), and choroidal thinning (-90.27{+/-}16.44 {micro}m) in the LIM group (all, P<0.001). Compared to the LIM group, exposure to 2h, 4h, or 6h of HL, RF, or HL+RF reduced myopic refraction in a duration-dependent manner, with RF being more effective than HL (P<0.05). Only 6h of HL+RF (not 2h or 4h) prevented LIM and was more effective than RF (P=0.004) or HL (P<0.001) in reducing myopic refraction, and more effective than HL (P<0.001) in reducing axial elongation. CONCLUSIONDaily exposure to 2h, 4h, or 6h of HL, RF, or HL+RF reduced lens-induced myopic refraction in a duration-dependent manner in chickens. Only 6h of HL+RF completely stopped LIM development. The synergetic effect of HL and RF is dependent on the duration of the interventions.

neuroscience↗

bioRxiv2022

The Structural Layers of the Porcine Iris Exhibit Inherently Different Biomechanical Properties

PurposeTo isolate the structural components of the ex vivo porcine iris tissue and to determine their biomechanical properties. MethodsThe porcine stroma and dilator tissues were separated, and their dimensions were assessed using optical coherence tomography (OCT). The stroma underwent flow test (n = 32) to evaluate for permeability using Darcys Law ({Delta}P = 2000 Pa, A = 0.0391 mm2), and both tissues underwent stress relaxation experiments ({varepsilon} = 0.5 with initial ramp of {delta}{varepsilon} = 0.1) to evaluate for their viscoelastic behaviours (n = 28). Viscoelasticity was characterised by the parameters {beta} (half width of the Gaussian distribution), {tau}m(mean relaxation time constant), E0 (instantaneous modulus) and E{infty} (equilibrium modulus). ResultsFor the stroma, the hydraulic permeability was 9.49 {+/-} 3.05 x 10-6 mm2/Pa{middle dot}s, and the viscoelastic parameters were {beta} = 2.50 {+/-} 1.40, and {tau}m = 7.43 {+/-} 4.96 s, with the two moduli calculated to be E0= 14.14 {+/-} 6.44 kPa and E{infty} = 6.08 {+/-} 2.74 kPa. For the dilator tissue, the viscoelastic parameters were {beta} = 2.06 {+/-} 1.33 and {tau}m = 1.28 {+/-} 1.27 s, with the two moduli calculated to be E0 = 9.16 {+/-} 3.03 kPa and E{infty} = 5.54 {+/-} 1.98 kPa. ConclusionWe have established a new protocol to evaluate the biomechanical properties of the structural layers of the iris. Overall, the stroma was permeable and exhibited smaller moduli than those of the dilator muscle. An improved characterisation of iris biomechanics may form the basis to further our understanding of angle closure glaucoma.

bioengineering↗

bioRxiv2021

Recovery from form-deprivation myopia in chicks is dependent upon the fullness and correlated colour temperature of the light spectrum

BackgroundTo evaluate the impact of full-spectrum light-emitting diodes (LEDs) mimicking sunlight on ocular axial elongation and refractive error development in a chicken model of myopia. MethodsA total of 39 chicks (Lohmann brown), 1 day-old, were randomly distributed into 3 groups. Animals were housed for 28 days in a temperature-controlled enclosure, under a 12/12h light/dark cycle of isoluminant ([~]285 Lux) fluorescent [n = 18, (4000K, FL-4000)] or Sunlike-LED [n=12, (4000K, SL-4000); n = 9, (6500K, SL-6500)] white lights. Myopia was induced monocularly in all chicks by random occlusion of one eye with a frosted diffuser, from day 1 post-hatching (D1) until D14. On D14, diffusers were removed, and recovery from myopia was monitored under the same experimental light condition. Axial length (AL), refractive status, choroidal thickness and anterior chamber depth were recorded on days 1, 7, 14, 22 and 28. Ex vivo scleral collagen fibre thicknesses were measured from scanning electron microscopy images. Differences in outcome measures between eyes and groups were compared using 2-way repeated-measures ANOVA. ResultsThere was no significant difference between groups in the AL and refraction of form-deprived (FD) eyes during form-deprivation (D1 to D14). FD eyes of animals raised under SL-4000 and SL-6500 recovered more rapidly from excessive axial elongation than those of animals raised under FL-4000, by D22 and D28. Correspondingly, the refractive status of FD eyes exposed to SL-4000 and SL-6500 was close to that of control eyes by D28. The choroid became thicker during recovery in FD eyes compared to control eyes, in all groups. Choroidal thickness was significantly greater in FD eyes of chickens raised under SL-6500 than in animals raised under FL-4000 (P < 0.01). The diameter of scleral collagen fibrils was significantly greater in recovering FD eyes of chickens raised under SL-6500, than in those raised under FL-4000 (P = 0.04) and SL-4000 (P = 0.002). ConclusionsCompared to fluorescent light, moderate intensities of full-spectrum Sunlike-LEDs can accelerate recovery from form-deprivation myopia in chickens, potentially through choroid-mediated pathways increasing the diameter of scleral collagen fibrils. This study highlights an important implication of the spectral content of white light on ocular growth and emmetropization.

neuroscience↗