Biology subjects

Cajochen, C.

Publications and source records attributed to Cajochen, C..

18 recordsLinked to original sources

bioRxiv2025

Physiologically-relevant light exposure and light behaviour in Switzerland and Malaysia

Light synchronises the internal clock with the external light-dark cycle. Keeping this alignment benefits health and prevents diseases. Quantifying light exposure is, therefore, vital for effective prevention. Since light exposure depends on photoperiod, culture, and behaviour, we investigated objective light exposure and individual light-related behaviour in Switzerland and Malaysia. In this observational field study, participants (N=39) wore a calibrated melanopic light logger at chest level for 30 consecutive days. At baseline and study end, the Pittsburgh Sleep Quality Index was assessed, and every 3 to 4 days, the Light Exposure Behaviour Assessment (LEBA) was filled. Our pre-registered analyses reveal that participants in Switzerland experienced brighter days (+3.16 times the average mel EDI) and spent more time (x1.9 times the duration) in daylight levels per hour of daylight, had [~]1.5h later bright light exposure in the afternoon, and stayed over 1h longer in dim light conditions before bedtime. LEBA scores did not differ between Malaysia and Switzerland, and LEBA items were stable over time. LEBA items also correlated with objective light exposure variables in Switzerland but not Malaysia, with a medium effect size (range of absolute r=0.32-0.48). These results highlight cultural and geographical differences in light exposure. We showed that LEBA can be related to actual light exposure and is ecologically informative, but this varies by culture.

neuroscience↗

bioRxiv2024

Reduced and Redundant: Information Processing of Prediction Errors during Sleep

During sleep, the human brain transitions to a sentinel processing mode, enabling the continued processing of environmental stimuli despite the absence of consciousness. Here, we employed advanced information-theoretic analyses, including mutual information (MI) and co-information (co-I), alongside event-related potential (ERP) and temporal generalization analyses (TGA), to characterize auditory prediction error processing across wakefulness and sleep. We hypothesized that a shared neural code would be present across sleep stages, with deeper sleep being associated with reduced information content and increased information redundancy. To investigate this, twenty-nine young healthy participants were exposed to an auditory local-global oddball paradigm during wakefulness and during an 8-hour sleep opportunity monitored via polysomnography in a cross-sectional study. We focused on local mismatch responses to a deviating fifth tone following four standard tones. ERP analyses showed that prediction error processing continued throughout all sleep stages (N1-N3, REM). Mutual information analyses revealed a substantial reduction in the amount of encoded prediction error information particularly during N3 and REM, although ERP amplitudes increased with deeper NREM sleep. In addition, we observed delayed information encoding during sleep and co-information analyses showed that neural dynamics became increasingly redundant with increasing sleep depth. Temporal generalisation analyses revealed a largely shared neural code between N2 and N3 sleep, although it differed between wakefulness and sleep. Here, we showed how the neural code of the sentinel processing mode changes from wake to light to deep sleep and REM, characterised by delayed processing, more redundant and less rich neural information in the human cortex as consciousness wanes. This altered stimulus processing reveals how neural information changes with the changes of consciousness states as we traverse the night.

neuroscience↗

bioRxiv2024

Sex and seasonal variations in melatonin suppression, and alerting response to light

Light influences human physiology and behaviour by regulating circadian rhythms, melatonin secretion, and alertness. Previous research has reported sex differences in melatonin secretion and circadian rhythms, possibly related to womens greater sensitivity to bright light. Other studies have suggested reduced photosensitivity and earlier circadian phases in summer than in winter in mid-latitude regions. This study explores the effects of sex, seasonality, and their combination on melatonin suppression and subjective sleepiness in response to moderate light exposure, considering prior light history and menstrual phases in females. We conducted a controlled, within-subject experiment with 48 healthy adults (18-35 years, 50% female) across different seasons. The study design included two 9-h laboratory sessions, with at least 5-day washout in between. Participants were exposed to dim and moderate light through a screen for 2 hours after their habitual bedtime. Female participants exhibited greater melatonin suppression (+4.69 %) but a lower alerting response (-6.00%) to moderate light compared to males. Both sexes demonstrated increased sensitivity to the NIF effects of light in winter, with stronger melatonin suppression (+18.05 %) and increased alertness (+7.60 %) compared to summer. While prior light history did not significantly impact melatonin suppression or alertness, it was associated with an earlier dim light melatonin onset (DLMO). Females during their luteal phase had earlier DLMO than those in their follicular phase. Our findings indicate an interaction between sex, seasonality, and light exposure in modulating melatonin suppression, emphasising the need for personalised light exposure recommendations according to individual biological and environmental contexts.

physiology↗

bioRxiv2024

Lack of evidence for the contribution of cone photoreceptors to human melatonin suppression and alerting response to light at night

Light exposure at night can suppress melatonin production and increase alertness, primarily through the action of melanopsin-containing intrinsically photosensitive retinal ganglion cells (ipRGCs). This study investigated whether cone photoreceptors also influence melatonin suppression and subjective alertness using non-visual metameric light emitted from a display. Forty-eight participants with normal trichromatic vision were exposed to three lighting conditions: a baseline (9 lxmEDI), constant background (149 lxmEDI), and cone-modulated flickering light targeting different cone combinations and post-receptoral channels (149 lxmEDI) for 2 hours after their habitual bedtime. Salivary melatonin levels and subjective alertness were measured throughout a 9-h protocol. Bayesian analysis showed that cone-modulated flickering light did not significantly affect melatonin suppression or alertness, providing evidence against the hypothesis that cone photoreceptors contribute to these non-visual effects of light. In conclusion, our results suggest cone photoreceptors do not play a measurable role in lights effects on melatonin suppression and subjective alertness at night.

physiology↗

bioRxiv2024

Afternoon to early evening bright light exposure reduces later melatonin production in adolescents

Whether light exposure during the day reduces non-visual light effects later in the evening has not been studied in adolescents. We investigate whether afternoon-early evening (AEE) light interventions (130 lx, 2500 lx, 4.5 hours, compared to 6.5 lx) would increase melatonin levels during later evening light exposure (130 lx) in a counterbalanced crossover study with 22 adolescents (14-17 years, 11 female). Contrary to our hypothesis, evening melatonin levels decreased after AEE bright light exposure, while sleepiness and vigilance were unaffected, and skin temperature showed no clear changes. The AEE light had acute alerting effects and bright light exposure in the 32 hours before laboratory entry was associated with higher evening melatonin and sleepiness. These findings suggest that bright AEE light increases alertness but may delay melatonin production by interfering with circadian rhythms. The study highlights the complex effects of light timing and its implications for managing adolescents light exposure.

neuroscience↗

bioRxiv2023

Effects of calibrated blue-yellow (-S+) changes in light on the human circadian clock

Evening exposure to short-wavelength light can acutely affect the circadian clock located in the suprachiasmatic nuclei, sleep, and alertness. The intrinsically photosensitive retinal ganglion cells (ipRGCs) expressing the photopigment melanopsin are thought to be the primary drivers of these effects. Much less is known about the contribution of the colour-sensitive cones. Using calibrated silent-substitution changes in light colour along the blue-yellow axis, we investigated whether mechanisms of colour vision affect the human circadian system and sleep. In a 32.5-h repeated within-subjects protocol, 16 healthy participants (8 women, 18-35 years old) were exposed to three different light scenarios for 1 h starting 30 min after habitual bedtime: a control condition ("background", 93.5 photopic lux), intermittently flickering yellow-bright light (1 Hz, 30s on-off, 123.5 photopic lux), and intermittently flickering blue-dim light (1 Hz, 30s on-off; 67.0 photopic lux). Importantly, there was no difference in melanopsin excitation (163.2{+/-}2.1 lux melanopic EDI) between the three lighting conditions, allowing us to determine the unique contribution of the blue-yellow colour system. Our analyses did not yield conclusive evidence for differences between the three lighting conditions regarding circadian melatonin phase delays, melatonin suppression, subjective sleepiness, psychomotor vigilance, or sleep. Thus, in this study, we found no evidence that evening light changing along the blue-yellow dimension under moderate light levels typical for room illumination has a major impact on the human circadian clock or sleep. Our work underscores the previously demonstrated primary role of melanopsin-containing ipRGCs in mediating these effects.

neuroscience↗

bioRxiv2022

Light targeting the melanopic system suppresses melatonin, but does not alter sleepiness, vigilance, sensory processing, or sleep

Pre-sleep exposure to short-wavelength light suppresses melatonin and decreases sleepiness with activating effects extending to sleep. This has mainly been attributed to melanopic effects, but mechanistic insights are missing. Thus, we investigated whether two light conditions only differing in the melanopic effects (123 vs. 59 lux melanopic EDI) differentially affect sleep besides melatonin. Additionally, we studied whether the light differentially modulates sensory processing during wakefulness and sleep. Twenty-nine healthy volunteers (18-30 years, 15 women) were exposed to two metameric light conditions (high-vs. low-melanopic, {approx}60 photopic lux) for 1 hour ending 50 min prior to habitual bed time. This was followed by an 8-h sleep opportunity with polysomnography. Objective sleep measurements were complemented by self-report. Salivary melatonin, subjective sleepiness, and behavioural vigilance were sampled at regular intervals. Sensory processing was evaluated during light exposure and sleep on the basis of neural responses related to violations of expectations in an oddball paradigm. We observed suppression of melatonin by {approx}14 % in the high-compared to the low-melanopic condition. However, conditions did not differentially affect sleep, sleep quality, sleepiness, or vigilance. A neural mismatch response was evident during all sleep stages, but not differentially modulated by light. Suppression of melatonin by light targeting the melanopic system does not automatically translate to acutely altered levels of vigilance or sleepiness or to changes in sleep, sleep quality, or basic sensory processing. Given contradicting earlier findings and the retinal anatomy, this may suggest that an interaction between melanopsin and cone-rod signals needs to be considered. Statement of SignificanceMetameric light allows to mechanistically investigate the contribution of one specific retinal receptor. Using this approach, we here investigated the effects of high-vs. low-melanopic light for 1 hour in the evening at ecologically valid screen illuminance ({approx}60 photopic lux). Going beyond earlier research, we also investigated effects on sleep. We found that despite significant suppression of melatonin, other endpoints including sleep and sleep quality were not differentially affected. This underlines that melatonin suppression does not automatically translate to alterations of sleep, sleepiness, or vigilance. Further, it suggests that melanopsin effects may need to be studied in the context of cone-rod signals. Future research should thus investigate the relevance of such an interaction, which may vary between endpoints.

neuroscience↗

bioRxiv2021

Time to recover from daily caffeine intake.

Caffeine elicits widespread effects in the central nervous system and is the most frequently consumed psychostimulant worldwide. First evidence indicates that, during daily intake, the elimination of caffeine may slow down and the primary metabolite, paraxanthine, may accumulate. The neural impact of such adaptions is virtually unexplored. In this report, we leveraged the data of a laboratory study with N= 20 participants and three within-subject conditions: caffeine (150 mg caffeine x 3/day x 10 days), placebo (150 mg mannitol x 3/day x 10 days), and withdrawal (caffeine x 9 days, afterwards placebo x 1 day). Using liquid chromatography-mass spectrometry coupled with tandem mass spectrometry, we determined the course of salivary caffeine and paraxanthine, measured regularly at day 10. We assessed grey matter (GM) intensity and cerebral blood flow (CBF) in the withdrawal condition as compared to their changes in caffeine in our previous report. The results indicate high remaining levels of paraxanthine and of caffeine carried overnight during daily intake, and the levels of paraxanthine remained higher than in placebo during withdrawal. After 36 h of withdrawal, the previously reported caffeine-induced GM reduction was partially mitigated, while CBF was elevated compared to placebo. Our findings unveil that conventional daily caffeine intake does not provide sufficient time to clear up psychoactive compounds and restore cerebral responses, even after 36 hours of abstinence. They also suggest investigating consequences of a paraxanthine accumulation during daily caffeine intake.

pharmacology and toxicology↗

bioRxiv2021

Working Memory Performance after Daily Caffeine Intake: Compromised Performance and Reduced Hippocampal Activity.

Neuroprotective effects of caffeine have been frequently reported in the context of disease and cognitive dysfunction as well as in epidemiological studies in humans. However, evidence on caffeine effects on neural and memory functions during daily intake in a healthy cognitive state remains scarce. This randomized double-blind placebo-controlled crossover study investigated working memory functions by N-back tasks and functional magnetic resonance imaging (fMRI) after daily caffeine intake compared to a placebo baseline and to acute caffeine withdrawal in 20 young healthy volunteers. Each volunteer was given 3 times 150 mg caffeine for 10 days in the daily caffeine condition, 3 times 150 mg mannitol for 10 days in the placebo condition, and 9-day caffeine plus 1-day mannitol in the acute withdrawal condition. During the 10th day, participants performed 4 N-back sessions (two loads each: 0- and 3-back) under controlled laboratory conditions. During the 4th session of N-Back (i.e. at 5.5 h, 36.5 h and > 10 days after the last caffeine intake in the caffeine, withdrawal, and placebo condition, respectively) we assessed blood-oxygen-level-dependent (BOLD) activity. During the entire 10th day, in 0-back tasks, we observed longer reaction times (RTs) in the withdrawal compared to the placebo (Cohens d = 0.7) and caffeine condition (Cohens d = 0.6), but no significant effects of conditions on error rates. In contrast, in 3-back tasks (controlled for 0-back), the RTs in the caffeine condition were longer compared to placebo (Cohens d = 0.6) and withdrawal (Cohens d = 0.5). Error rates were higher during both caffeine and withdrawal conditions compared to placebo (Cohens d of both contrasts = 0.4). Whole-brain analyses on fMRI data did not reveal significant condition-dependent differences in activities between task loads. Across task loads, however, we observed a reduced hippocampal activation (Cohens d = -1.3) during the caffeine condition compared to placebo, while no significant difference in brain activities between withdrawal and placebo conditions. Taken together, the worse working memory function and the hippocampal hypoactivation implicate a potential detrimental effect of daily caffeine intake on neurocognitive functions of healthy adults. Moreover, they echo the hippocampal volumetric reduction reported previously in the same volunteers. Lastly, acute withdrawal from daily caffeine intake impairs both low-order cognitive processes and working memory performance. Taking earlier studies on acute caffeine effects into account, our findings indicate that daily caffeine intake elicits a dynamic change in cerebral activities during the course of repeated consumption, with unknown consequences in the long run.

neuroscience↗

bioRxiv2020

Enhancing daily light exposure increases the antibody response to influenza vaccination in patients with dementia

Enhancing lighting conditions in institutions for individuals with dementia improves their sleep, circadian rhythms and well-being. Here, we tested whether a greater long-term daily light exposure supports the immune response to the annual influenza vaccination. Eighty older institutionalised patients suffering from dementia (54 women and 26 men) continuously wore an activity tracker for 8 weeks to assess individual light exposure and rest-activity cycles. The patients immune response was analysed from two blood samples taken before and 4 - 5 weeks after the annual influenza vaccination. Individual antibody concentrations to three influenza virus strains (H3N2, H1N1, IB) were quantified via hemagglutination inhibition assays. By quantifying individual light exposure profiles (including daylight), we classified the patients into a low and a high light exposure group based on a median illuminance of 392.6 lux. The two light exposure groups did not differ in cognitive impairment severity, age or gender distribution. However, patients in the high light exposure group showed a significantly greater circadian rest-activity amplitude (i.e., more daytime activity and less nighttime activity) along with a significantly greater antibody titer increase to the H3N2 vaccine than patients in the low light exposure group, despite similar pre-vaccination concentrations. Sufficient seroprotective responses to all three influenza virus strains were attained for [≥] 75% of participants. These data provide first evidence for a potentially enhanced immune response in patients with dementia when they received more daily light. Increasing daily light exposure may have beneficial effects on the human immune system, either directly or via circadian rhythm stabilisation.

immunology↗

bioRxiv2020

Regular caffeine intake attenuates REM sleep promotion and sleep quality in healthy men

Acute caffeine intake can attenuate homeostatic sleep pressure and worsen sleep quality. Besides, caffeine intake - particularly in high doses and close to bedtime - may also affect circadian-regulated REM sleep promotion, an important determinant of subjective sleep quality. However, it is not known whether such changes persist under chronic caffeine consumption during daytime. Twenty male caffeine consumers (26.4 {+/-} 4 years old, habitual caffeine intake 478.1 {+/-} 102.8 mg/day) participated in a double-blind crossover study. Each volunteer completed a caffeine (3 x 150 mg caffeine daily), a withdrawal (3 x 150 mg caffeine for eight days then placebo), and a placebo condition. After ten days of controlled intake and a fixed sleep-wake cycle, we recorded 8 h of electroencephalography starting 5 h after habitual bedtime (i.e., start on average at 04:22 am which is around the peak of circadian REM sleep promotion). A 60 min evening nap preceded each sleep episode and reduced high sleep pressure levels. While total sleep time and sleep architecture did not significantly differ between the three conditions, REM latency was longer after daily caffeine intake compared to both placebo and withdrawal. Moreover, the accumulation of REM sleep proportion was slower, and volunteers reported more difficulties at awakening after sleep and feeling more tired upon wake-up in the caffeine condition compared to placebo. Our data indicate that besides acute also regular daytime caffeine intake affects REM sleep regulation in men. We have evidence that regular caffeine intake during daytime weakens circadian sleep promotion when compared to placebo. Moreover, the observed caffeine-induced deterioration in the quality of awakening may suggest a potential motive to reinstate caffeine intake after sleep.

neuroscience↗

bioRxiv2020

Rest-activity cycles and melatonin phase angle of circadian entrainment in people without cone-mediated vision

BackgroundLight exposure entrains the circadian clock through the intrinsically photosensitive retinal ganglion cells, which sense light in addition to the cones and rods. In congenital achromatopsia (ACHM; prevalence 1:30-50,000), the cone system is non-functional, resulting in severe light avoidance and photophobia at daytime light levels. How this condition affects circadian and neuroendocrine responses to light is not known. MethodsIn genetically confirmed ACHM patients (n=7; age 30-72 years; 6 women, 1 male), we examined survey-assessed sleep/circadian phenotype (PSQI, ESS, MEQ, MCTQ), self-reported visual function (NEI-VFQ-25), sensitivity to light (VLSQ-8) and use of spectral filters that modify chronic light exposure. In all but one patient, we measured rest-activity cycles using actigraphy over 3 weeks and measured the melatonin phase angle of entrainment using the dim-light melatonin onset (DLMO). ResultsACHM patients experience a severely attenuated light-dark cycle due to severe light sensitivity and habitual use of filters to reduce retinal illumination. In aggregate, both MEQ and MCTQ indicated a tendency to late chronotype. We found regular rest-activity patterns in all patients and normal phase angles of entrainment in participants with a measurable DLMO. ConclusionsOur results reveal that a functional cone system and exposure to daytime light intensities are not necessary for regular behavioural and hormonal entrainment, even when survey-assessed sleep and circadian phenotype indicated a tendency for a late chronotype and sleep problems in our ACHM cohort. Our results can be explained by an adaptation mechanism in circadian photoreception which adjusts to the range of habitual light exposures.

neuroscience↗

bioRxiv2020

The impact of daily caffeine intake on nighttime sleep: signs of overnight withdrawal?

Acute caffeine intake can delay sleep initiation and reduce sleep intensity, particularly when consumed in the evening. However, it is not clear whether these sleep disturbances disappear when caffeine is continuously consumed during daytime, which is common for most coffee drinkers. To address this question, we investigated the sleep of twenty male young habitual caffeine consumers during a double-blind, randomized, crossover study including three 10-day conditions: caffeine (3 x 150 mg caffeine daily), withdrawal (3 x 150 mg caffeine for eight days, then switch to placebo), and placebo (3 x placebo daily). After nine days of continuous treatment, electroencephalographically (EEG)-derived sleep structure and intensity were recorded during a scheduled 8-h nighttime sleep episode starting 8 (caffeine condition) and 15 h (withdrawal condition) after the last caffeine intake. Upon scheduled wake up time, subjective sleep quality and caffeine withdrawal symptoms were assessed. Unexpectedly, neither polysomnography-derived total sleep time, sleep latency, sleep architecture, nor subjective sleep quality differed among placebo, caffeine, and withdrawal conditions. Nevertheless, EEG power density in the sigma frequencies (12-16 Hz) during non-rapid eye movement (NREM) sleep was reduced in both caffeine and withdrawal conditions when compared to placebo. These results indicate that daily caffeine intake in the morning and afternoon hours does not strongly impair nighttime sleep structure or subjective sleep quality in healthy good sleepers who regularly consume caffeine. The reduced EEG power density in the sigma range might represent early signs of overnight withdrawal from the continuous presence of the stimulant during the day. Statement of SignificanceCaffeine consumption is highly prevalent worldwide and has been repeatedly shown to acutely disrupt sleep, particularly when consumed after several days of abstinence or close to bedtime. However, commonly, caffeine is consumed daily and during daytime. Our well-controlled laboratory study revealed that this common pattern of intake affects nighttime sleep differently: While slow-wave sleep duration or slow-wave activity were rather similar compared to placebo, caffeine intake surprisingly reduced EEG power density in the sigma frequencies. In the light of earlier studies, this might present early signs of caffeine withdrawal which occurs due to overnight caffeine abstinence. The present findings provide novel insights into the impact of daily presence and nightly abstinence of caffeine on nighttime sleep in regular consumers.

neuroscience↗

bioRxiv2020

Changing color and intensity of LED lighting across the day impacts on human circadian physiology, sleep, visual comfort and cognitive performance

We examined whether dynamic light across a scheduled 16-h waking day influences cognitive performance, visual comfort, melatonin secretion, sleepiness and sleep under strictly controlled laboratory conditions of 49-h duration. Participants spent the first 5-h in the evening under standard lighting, followed by an 8-h nocturnal sleep episode at habitual bedtimes. Thereafter volunteers either woke up with static daylight LED (100 lux and 4000 Kelvin) or with a dynamic daylight LED that changed color (2700 - 5000 Kelvin) and intensity (0 - 100 lux) across the scheduled 16-h waking day. This was followed by an 8-h nocturnal treatment sleep episode at habitual bedtimes. Thereafter, volunteers spent another 12-h either under static or dynamic light during scheduled wakefulness. Under dynamic light, evening melatonin levels were less suppressed 1.5hours prior to usual bedtime, and participants felt less vigilant in the evening compared to static light. Sleep latency was significantly shorter in both the baseline and treatment night compared to the static light condition while sleep structure, sleep quality, cognitive performance and visual comfort did not significantly change. Our results support the recommendation of using blue-depleted light and low illuminances in the late evening, which can be achieved by a dynamically changing daylight LED solution.

physiology↗

bioRxiv2019

Caffeine-induced Plasticity of Grey Matter Volume in Healthy Brains: A placebo-controlled multimodal within-subject study

Disturbed sleep homeostatic states have been found to alter neuronal homeostasis and reduce grey matter (GM) volume. Caffeine intake that interferes with sleep homeostasis through antagonizing adenosine receptors can impair hippocampal synaptic strength, neurogenesis, as well as memory and learning in rats. In this study, reduced medial temporal GM volume was observed after daily caffeine intake in humans (3 x 150 mg x 10 days compared to 10-day placebo administration). The potential bias from reduced cerebral blood flow was controlled, and the GM reduction was independent of the change in sleep pressure. A decrease in working memory during daily caffeine intake was observed, albeit no association with the magnitude of GM changes. The findings indicate that daily caffeine intake might induce rapid cerebral plasticity and be detrimental for higher order cognitive performance in the long run. They may call into question whether the neuroprotective effects of caffeine found in acute or low dose administration in animals are generalizable onto the daily usage in humans.

neuroscience↗

bioRxiv2019

No evidence for an S cone contribution to the human circadian response to light

Exposure to even moderately bright, short-wavelength light in the evening can strongly suppress the production of melatonin and can delay our circadian rhythm. These effects are mediated by the retinohypothalamic pathway, connecting a subset of retinal ganglion cells to the circadian pacemaker in the suprachiasmatic nucleus (SCN) in the brain. These retinal ganglion cells directly express the photosensitive protein melanopsin, rendering them intrinsically photosensitive (ipRGCs). But ipRGCs also receive input from the classical photoreceptors -- the cones and rods. Here, we examined whether the short-wavelength-sensitive (S) cones contribute to circadian photoreception by using lights which differed exclusively in the amount of S cone excitation by almost two orders of magnitude (ratio 1:83), but not in the excitation of long-wavelength-sensitive (L) and medium-wavelength-sensitive (M) cones, rods, and melanopsin. We find no evidence for a role of S cones in the acute alerting and melatonin supressing response to evening light exposure, pointing to an exclusive role of melanopsin in driving circadian responses.

neuroscience↗

bioRxiv2019

Caffeine-dependent changes of sleep-wake regulation: evidence for adaptation after repeated intake

To enhance wakefulness, daily consumption of caffeine in the morning and afternoon is highly common. However, it is unknown whether such a regular intake pattern affects timing and quality of wakefulness, as regulated by an interplay of circadian and sleep-homeostatic mechanisms. Thus, we investigated the effects of daily caffeine intake and its withdrawal on circadian rhythms and wake-promotion in 20 male young habitual caffeine consumers. We applied a double-blind, within-subject design with a caffeine (150 mg, 3 x daily), a placebo, and a withdrawal condition each lasting ten days. Starting on day nine of treatment, salivary melatonin and cortisol, evening nap sleep, as well as sleepiness and vigilance performance throughout day and night were quantified during 43 h under controlled laboratory conditions. Neither the time course of melatonin (i.e., onset, amplitude, or area under the curve) nor the time course of cortisol were significantly affected by caffeine intake or its withdrawal. During withdrawal, however, volunteers reported increased sleepiness, showed more attentional lapses, as well as polysomnography-derived markers of elevated sleep propensity in the late evening compared to both, placebo and caffeine conditions. Thus, the typical timing of habitual caffeine intake in humans may not necessarily shift circadian phase nor lead to clear-cut benefits in alertness. The time-of-day independent effects of caffeine withdrawal suggest an adaptation to the substance, presumably in the homeostatic aspect of sleep-wake regulation.

neuroscience↗

bioRxiv2019

Visual and non-visual properties of filters manipulating short-wavelength light

Optical filters and tints manipulating short-wavelength light (so-called \"blue-blocking\" or \"blue-attenuating\") are used as a remedy for a range of ocular, retinal, neurological and psychiatric disorders. In many cases, the only available quantification of the optical effects of a given optical filter is the spectral transmittance, which specifies the amount of light transmitted as a function of wavelength. Here, we propose a novel physiologically relevant and retinally referenced framework for quantifying the visual and non-visual effects of these filters, incorporating the attenuation of luminance (luminance factor), the attenuation of melanopsin activation (melanopsin factor), the shift in colour, and the reduction of the colour gamut (gamut factor). We examined a novel data base of optical transmittance filters (n=120) which were digitally extracted from a variety of sources and find a large diversity in the alteration of visual and non-visual properties. We suggest that future studies and examinations of the physiological effects of optical filters quantify the visual and non-visual effects of the filters beyond the spectral transmittance, which will eventually aid in developing a mechanistic understanding of how different filters affect physiology.

neuroscience↗