Intermittent Light Stimuli Research Articles

Intermittent Light Exposures in Humans: A Case for Dual Entrainment in the Treatment of Alzheimer's Disease.

Circadian sleep disorders are common among American adults and can become especially acute among older adults, especially those living with Alzheimer's disease (AD) and mild cognitive impairment (MCI), leading to the exacerbation of symptoms and contributing to the development and advancement of the diseases. This review explores the connections between circadian sleep disorders, cognition, and neurodegenerative disease, offering insights on rapidly developing therapeutic interventions employing intermittent light stimuli for improving sleep and cognition in persons with AD and MCI. Light therapy has the potential to affect sleep and cognition via at least two pathways: (1) a regular and robust light-dark pattern reaching the retina that promotes circadian phase shifting, which can promote entrainment and (2) 40 Hz flickering light that promotes gamma-wave entrainment. While this is a new area of research, preliminary evidence shows the potential of dual circadian and gamma-wave entrainment as an important therapy not only for those with AD, but for others with cognitive impairment.

Effect of light on blinking in patients with idiopathic isolated blepharospasm

ObjectiveMelanopsin may be involved in the pathophysiology of photophobia in idiopathic isolated blepharospasm. We assessed the efficacy of blocking wavelengths of melanopsin absorption to reduce blinking in blepharospasm as a possible surrogate for photophobia. MethodsTwenty-one participants (11 blepharospasm and 10 healthy controls) were studied. There were three sessions: (1) a baseline condition to measure the blink rate (BR) without intervention; (2) two conditions where the participants received intermittent light stimuli with high or low intensity without wearing study lenses; (3) four conditions in which the participants received intermittent light stimuli with high intensity while wearing one of four different lenses: tinted lenses with neutral gray or FL-41, or coated lenses that block 480-nm or 590-nm wavelength. The primary outcome measure was the BR. ResultsThe blepharospasm group blinked more frequently than controls in dim room conditions. Patients reported greater photosensitivity compared to controls based on the questionnaire and exhibited a higher BR with intermittent light stimuli. The BR decreased for both groups when using 480-nm and 590-nm blocking lenses. In the patients, 480-nm and 590-nm blocking lenses reduced the mean BR by 9.6 blink/min and 10.3 blink/min, respectively, while in the control group, the mean BR decreased by 4.4 blink/min and 4.3 blink/min, respectively. ConclusionsBlepharospasm patients had increased BR with light stimuli which decreased with 590-nm and 480-nm blocking lenses. The 480-nm- and 590-nm- coated lenses might have therapeutic potential in treating photophobia although BR does not appear to be an optimal biomarker for photophobia.

Critical Fusion Frequency and Audio-Visual Reaction Time as a Function of Age


 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Background & objective
 Aging is associated with physiological changes in functioning of different parts of the body. One of the changes commonly seen in elderly persons is slowness of the movements. Many studies concluded that audio-visual reaction time (RT) increases with age. Critical fusion frequency (CFF) is the frequency at which an intermittent light stimulus appears to be completely steady to the observer. It is been observed that CFF decreases with age. But whether this decrease is a progressive phenomenon is not clear. Hence, the present study was designed to investigate CFF in various age groups.
 Materials & method
 The study involved hundred subjects within the age group of 20–70 years. Subjects were divided into five age groups. Audio-visual reaction time and critical fusion frequency were measured. Data was statistically analyzed by using one way ANOVA for group wise changes in RT and CFF. Relationship between visual RT and CFF was found out by Pearson's coefficient of correlation.
 Results
 Visual RT and Audio RT were positively and significantly correlated with age whereas CFF was significantly and negatively correlated with age in male and females separately as well as when combined together. (p<0.001)
 Conclusion
 From our study we conclude that the RT increases and CFF decreases with age. These changes are similar in both male and female subjects.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Critical Fusion Frequency and Audio-Visual Reaction Time as a Function of Age

Background & objective Aging is associated with physiological changes in functioning of different parts of the body. One of the changes commonly seen in elderly persons is slowness of the movements. Many studies concluded that audio-visual reaction time (RT) increases with age. Critical fusion frequency (CFF) is the frequency at which an intermittent light stimulus appears to be completely steady to the observer. It is been observed that CFF decreases with age. But whether this decrease is a progressive phenomenon is not clear. Hence, the present study was designed to investigate CFF in various age groups. Materials & method The study involved hundred subjects within the age group of 20–70 years. Subjects were divided into five age groups. Audio-visual reaction time and critical fusion frequency were measured. Data was statistically analyzed by using one way ANOVA for group wise changes in RT and CFF. Relationship between visual RT and CFF was found out by Pearson's coefficient of correlation. Results Visual RT and Audio RT were positively and significantly correlated with age whereas CFF was significantly and negatively correlated with age in male and females separately as well as when combined together. (p<0.001) Conclusion From our study we conclude that the RT increases and CFF decreases with age. These changes are similar in both male and female subjects.

Effect of Intermittent versus Continuous Light Exposure on Pupillary Light Response, As Evaluated by Pupillometry.

Continuous and intermittent stimuli with green light affect the pupillary light response (PLR) differently. Since the majority of pupillometric studies use blue and red lights, we investigated the effect of continuous and intermittent stimulations on the PLR using red and blue lights. Seventeen healthy subjects underwent continuous- and intermittent light stimuli, using red (643 nm) and blue light (463 nm). To avoid the influence of pupil size on the amount of light entering the eye, the procedures were repeated with the stimulus-eye in dilated condition. The maximal pupillary constriction and the early redilation phase of post-illumination pupillary response (PIPREarly) represented the mixed response of melanopsin and rod-cone photoreceptors. The late redilation phase of PIPR (PIPRLate) was the marker of melanopsin-containing retinal ganglion cells. Intermittent stimuli with blue light elicited significantly larger maximal contraction during dilated condition (P = 0.001), and larger sustained pupillary contraction under dilated as well as undilated condition (P < 0.001) compared to continuous light exposure. Except the PIPREarly during undilated condition, none of the PIPR metrics were significantly different between intermittent and continuous blue light stimuli. Intermittent red light stimuli elicited also a more sustained pupillary contraction regardless of mydriatic instillation (P ≤ 0.02). In addition, intermittent red light exposure resulted in a slightly larger PIPREarly under undilated condition (P = 0.02) and a slightly larger PIPRLate under dilated condition (P = 0.049). Except the PIPRLate to continuous red light stimulus, all PIPR parameters were larger when the light was presented after induction of unilateral mydriasis. PLR parameters during and after light exposures depend on both the light stimulation mode and the entrance pupillary size.

Zjawisko fotowrażliwości u dzieci i młodzieży z napięciowymi bólami głowy – jego objawy i sposoby zapobiegania. Doświadczenia własne

BackgroundEEG is one of the basic tests in neurological diagnostics. Photostimulation trial is considered to play an important role during the test. It bases on applying an intermittent light stimulus with the use of a stroboscopic lamp. The occurrence of EEG changes in response to photostimulation is called photosensitivity. AimEvaluation of the efficacy of a photostimulation trial in the activation of paroxysmal changes in EEG recordings in children and adolescents with tension headaches. The study also aimed to evaluate an influence of the use of glasses with Z1 lenses (Italian blue) on the reduction of the photosensitivity. Material and methodsThe analysis included 51 patients with tension headaches aged 5–18 years – 12 boys (23%) and 39 girls (76%) diagnosed with photosensitivity of I, II, III or IV type. All patients underwent EEG examination in accordance with medical indications (tension headaches). After the registration of a photosensitivity, in the course of the same study, the EEG recording was repeated with the use of glasses equipped with Z1 filter lenses. ResultsA complete or partial disappearance, or the reduction at least by half of a period or an amplitude of discharges with Z1 filter glasses compared to baseline examination was considered the criterion of an effectiveness of Italian blue lenses. A positive response was achieved in 41 patients (80%). Complete resolution of discharges was achieved in 26 patients (50%) and partial reduction was observed in 15 patients (29%). Ten patients did not respond to Z1 lenses. ConclusionThe use of Italian blue lenses allows to improve EEG recordings in a large percentage of pediatric patients with tension headaches. The use of Z1 lenses can be considered an effective alternative in the reduction adverse effects of the photosensitivity in children and adolescents.

Melanopsin and Rod–Cone Photoreceptors Play Different Roles in Mediating Pupillary Light Responses during Exposure to Continuous Light in Humans

In mammals, the pupillary light reflex is mediated by intrinsically photosensitive melanopsin-containing retinal ganglion cells that also receive input from rod-cone photoreceptors. To assess the relative contribution of melanopsin and rod-cone photoreceptors to the pupillary light reflex in humans, we compared pupillary light responses in normally sighted individuals (n = 24) with a blind individual lacking rod-cone function. Here, we show that visual photoreceptors are required for normal pupillary responses to continuous light exposure at low irradiance levels, and for sustained pupillary constriction during exposure to light in the long-wavelength portion of the visual spectrum. In the absence of rod-cone function, pupillomotor responses are slow and sustained, and cannot track intermittent light stimuli, suggesting that rods/cones are required for encoding fast modulations in light intensity. In sighted individuals, pupillary constriction decreased monotonically for at least 30 min during exposure to continuous low-irradiance light, indicating that steady-state pupillary responses are an order of magnitude slower than previously reported. Exposure to low-irradiance intermittent green light (543 nm; 0.1-4 Hz) for 30 min, which was given to activate cone photoreceptors repeatedly, elicited sustained pupillary constriction responses that were more than twice as great compared with exposure to continuous green light. Our findings demonstrate nonredundant roles for rod-cone photoreceptors and melanopsin in mediating pupillary responses to continuous light. Moreover, our results suggest that it might be possible to enhance nonvisual light responses to low-irradiance exposures by using intermittent light to activate cone photoreceptors repeatedly in humans.

Relation of photosensitivity to epileptic syndromes.

Photosensitivity is the most common mode of seizure precipitation. It is age-related, more frequent in females, and most often found in generalised epilepsies. Little is known about its relation to individual epileptic syndromes. This study on 1062 epileptic patients who had 4007 split screen video EEG investigations revealed that the relation to generalised epilepsy is even more close than generally believed. Versive seizures with visual hallucinations was the only focal seizure type related to photosensitivity. Of the syndromes of generalised epilepsy, only childhood absence epilepsy, juvenile myoclonic epilepsy, and epilepsy with grand mal on awakening were related to photosensitivity. The closest correlation was with juvenile myoclonic epilepsy. This is confirmed by a relation to the poly-spike wave pattern, and by an increase of myoclonic seizures by intermittent light stimuli. No relation was found with early childhood syndromes of generalised epilepsy, or generalised tonic-clonic seizures in the evening, or, most remarkably, with juvenile absence epilepsy. In generalised epilepsies with onset around puberty, photosensitivity could thus act as a pathoplastic factor. The female preponderance in both childhood absences and photosensitivity could be due to the same unknown factor.

EEG evaluation of a sleep recorder.

Sleep disorders are important diagnostic and therapeutic aspects of many common psychiatric syndromes. Clinicians have to be content with the patients' own assessment of their sleep patterns, or at the best, those of a night nurse; both methods are known to be unreliable, particularly where insomnia is present (Kuper et al., 1970). In a previous paper, Johnson and Kitching (1972) described a simple device for assessing the duration of sleep in ward situations. It depended upon the patient's ability to signal wakefulness by pressing a mechanical switch in response to an intermittent light stimulus throughout the night. This was considered to indicate a level of cerebral arousal compatible with wakefulness: failure to respond to the light stimulus indicated that the patient's level of cerebral arousal was lowered to the level of ‘sleep‘. A number of objections were anticipated, however, which might invalidate these assumptions. Most important of these were: (i)The intermittent occurrence of the light stimulus, every 15–20 minutes, limits the device to an approximation of the duration of sleep. The system of scoring was to assume a period of 10 minutes of sleep on either side of a missed stimulus.(ii)The possibility that the patient could press the mechanical switch in response to the light stimulus whilst in Stage I or even Stage II of sleep (Rechtschaffen et al., 1968) without returning to wakefulness.(iii)The intermittent light stimulus might itself act as a disruptive stimulus to sleep, producing arousal and thus altering the sleep level.

Observations in photosensitive children with and without epilepsy.

The course of convulsive disease in 195 photosensitive children was analysed. Of these, 168 were suffering from cerebral seizures and 27 from various other disorders. Only four of the patients occasionally exhibited photogenic seizures. In all the other cases the cerebral seizures occurred independently of intermittent light stimuli. 1. The clinical picture of photosensitive epilepsy varies widely. Virtually all known forms of seizures and courses of illness may be seen. In the group investigated, febrile and afebrile grand mal attacks predominated. Focal seizures and petit mal followed in third and fourth place respectively. 2. Photosensitive epilepsies are more common in females than in males. 3. The course of photosensitive epilepsy is often highly malignant. This applies especially when focal symptoms are present and when the onset of the disease took place after the fifth year of life. 4. A total of 67 per cent of the patients first suffered seizures before the sixth year of life, i.e. before the age of maximum penetrance of photosensitivity. 5. Investigation of the family histories of the patients indicated that the appearance of the disease in early childhood was affected by additional genetic factors, probably independent of photosensitivity itself. 6. Photosensitivity is to be regarded as a symptom of a gene-dependent functional disorder. The activability of this via optic afferents is markedly age-linked.

Effect of Photoperiods on the Reactions of Juvenile Atlantic Salmon (Salmo salarL.) to Light Stimuli

The reactions to light stimuli of juvenile Atlantic salmon exposed to photoperiods (light-exposed fish) and those exposed to control conditions (control fish) were compared. The light-exposed fish showed more activity and reacted more readily to stimuli than the control fish. Both the control and light-exposed fish exhibited a negative phototaxis at all light intensities except the very lowest where a slight positive phototaxis was obvious. The intensity of an intermittent light stimulus had very little effect on the intensity of the reaction in the light-exposed fish, while the control fish showed an increase in the intensity of the reaction with an increase in the intensity of the light stimulus. The control fish showed an increase in the reaction to the intermittent light stimulus the longer the stimulus was applied at the higher levels of stimulation, while the light-exposed fish showed this behavior at the lower levels of stimulation. The reactions to continuous light were similar to the reactions to intermittent light stimuli, but the light-exposed fish reacted more quickly to continuous light than the control fish. These differences in behavior are attributed to the increased activity and sensitivity of the light-exposed fish, resulting from their exposure to photoperiods.

INTERMITTENT LIGHT STIMULATION AND FLICKER SENSATION

Flicker sensation depends on the frequency of the intermittent light stimulus, but the frequency required for a given criterion of flicker sensation shows a marked variability for different occasions with the same observer, or for different observers. This variability was studied using the multiple criterion technique, flicker judgments being obtained from twenty subjects on a number of occasions. In one set of experiments the whole visual field was stimulated, in another a field approximately 20°×30°. Four criteria of flicker sensation were employed including the customary criterion of ‘ just perceptible ’ flicker. The results showed that : (a) Small changes in stimulus frequency cause large differences in the noticeability of flicker and in the sensation of discomfort caused by flicker.. (b) Large changes in stimulus frequency cause little change in the apparent frequency of flicker, which remains constant around 16 c.p.s. (c) As stated above, sensitivity varies markedly both between subjects and betwee...

Benham's top and the colour phenomena resulting from interaction with intermittent light stimuli

Benham's top and the colour phenomena resulting from interaction with intermittent light stimuli