Optimal flickering light stimulation for entraining gamma waves in the human brain.
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ABSTRACT:
SUBMITTER: Lee K
PROVIDER: S-EPMC8355349 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:With aging, optimal parameters of flickering light stimulation (FLS) for gamma entrainment may change in the eyes and brain. We investigated the optimal FLS parameters for gamma entrainment in 35 cognitively normal old adults by comparing event-related synchronization (ERS) and spectral Granger causality (sGC) of entrained gamma rhythms between different luminance intensities, colors, and flickering frequencies of FLSs. ERS entrained by 700 cd/m2 FLS and 32 Hz or 34 Hz FLSs was stronger than that entrained by 400 cd/m2 at Pz (p < 0.01) and 38 Hz or 40 Hz FLSs, respectively, at both Pz (p < 0.05) and Fz (p < 0.01). Parieto-occipital-to-frontotemporal connectivities of gamma rhythm entrained by 700 cd/m2 FLS and 32 Hz or 34 Hz FLSs were also stronger than those entrained by 400 cd/m2 at Pz (p < 0.01) and 38 Hz or 40 Hz FLSs, respectively (p < 0.001). ERS and parieto-occipital-to-frontotemporal connectivities of entrained gamma rhythms did not show significant difference between white and red lights. Adverse effects were comparable between different parameters. In older adults, 700 cd/m2 FLS at 32 Hz or 34 Hz can entrain a strong gamma rhythm in the whole brain with tolerable adverse effects.
| S-EPMC9481621 | biostudies-literature
Project description:Recent studies indicate therapeutic benefits of electrical stimulation in cases of specific ophthalmic diseases that are associated with dysfunctional ocular microcirculation. This suggests effects of electrical stimulation on vascular functions. In the present study, we investigated the effects of electrical stimulation on retinal vessel reactions using dynamic vessel analysis (DVA). Eighty healthy subjects were randomly assigned to one of three groups receiving electrical stimulation with different current intensities: 400 ?A (n = 26); 800 ?A (n = 27); 1200 ?A (n = 27). The electrode montage for electrical stimulation consisted of a ring-shaped active electrode surrounding one eye and a square return electrode at the occiput. Rectangular, monophasic, positive current pulses were applied at 10 Hz for a duration of 60 s per stimulation period. DVA was used to observe the stimulation-induced reactions of retinal vessel diameters in response to different provocations. In three DVA measurements, three stimulus conditions were investigated: flicker light stimulation (FLS); electrical stimulation (ES); simultaneous electrical and flicker light stimulation (ES+FLS). Retinal vasodilation caused by these stimuli was compared using paired t-test. The subjects receiving electrical stimulation with 800 ?A showed significantly increased retinal vasodilation for ES+FLS compared to FLS (p < 0.05). No significant differences in retinal vessel reactions were found between ES+FLS and FLS in the 400 and 1200 ?A groups. No retinal vasodilation was observed for ES for all investigated current intensities. The results indicate that positive pulsed electrical stimulation of an adequate intensity enhances the flicker light-induced retinal vasodilation.
| S-EPMC6817672 | biostudies-literature
Project description:PurposeIntrinsically photosensitive retinal ganglion cells (ipRGCs) mediate nonimage-forming visual functions such as pupillary constriction and circadian photoentrainment. Optimizing daytime nonimage-forming photostimulation has health benefits. We aimed to enhance ipRGC excitation using flickering instead of steady light.MethodsHuman subjects were tested with a three-dimensional matrix of flickering 463-nm stimuli: three photon counts (13.7, 14.7 and 15.7 log photons cm(-2)), three duty cycles (12%, 47%, and 93%) and seven flicker frequencies (0.1, 0.25, 0.5, 1, 2, 4, and 7 Hz). Steady-state pupil constrictions were measured.ResultsAmong stimuli containing 13.7 log photons cm-2, the one flickering at 2 Hz with a 12% duty cycle evoked the greatest pupil constriction of 48% ± 4%, 71% greater than that evoked by an equal-intensity (12.3 log photons cm(-2) s(-1)) continuous light. This frequency and duty cycle were also best for 14.7 log photons cm-2 stimuli, inducing a 58% ± 4% constriction which was 38% more than that caused by an equal-intensity (13.3 log photons cm(-2) s(-1)) constant light. For 15.7 log photons cm-2 stimuli, the 1-Hz, 47% duty cycle flicker was optimal although it evoked the same constriction as the best 14.7 log photons cm(-2) flicker.ConclusionsPupillary constriction depends on flicker frequency and duty cycle besides intensity. Among the stimuli tested, the one with the lowest photon count inducing a maximal response is 13.3 log photons cm(-2) s(-1) flickering at 2 Hz with 12% duty cycle. Our data could guide the design of healthier architectural lighting and better phototherapy devices for treating seasonal affective disorder and jet lag.
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Project description:Organisms have evolved under stable natural lighting regimes, employing cues from these to govern key ecological processes. However, the extent and density of artificial lighting within the environment has increased recently, causing widespread alteration of these regimes. Indeed, night-time electric lighting is known significantly to disrupt phenology, behaviour, and reproductive success, and thence community composition and ecosystem functioning. Until now, most attention has focussed on effects of the occurrence, timing, and spectral composition of artificial lighting. Little considered is that many types of lamp do not produce a constant stream of light but a series of pulses. This flickering light has been shown to have detrimental effects in humans and other species. Whether a species is likely to be affected will largely be determined by its visual temporal resolution, measured as the critical fusion frequency. That is the frequency at which a series of light pulses are perceived as a constant stream. Here we use the largest collation to date of critical fusion frequencies, across a broad range of taxa, to demonstrate that a significant proportion of species can detect such flicker in widely used lamps. Flickering artificial light thus has marked potential to produce ecological effects that have not previously been considered.
| S-EPMC4038456 | biostudies-literature
Project description:In shallow water, downwelling light is refracted from surface waves onto the substrate creating bands of light that fluctuate in both time and space, known as caustics. This dynamic illumination can be a visual hindrance for animals in shallow underwater environments. Animals in such habitats may have evolved to use polarization vision for discriminating objects while ignoring the variations in illumination caused by caustics. To explore this possibility, crabs (Carcinus maenas) and cuttlefish (Sepia officinalis), both of which have polarization vision, were presented with moving stimuli overlaid with caustics. Dynamic caustics inhibited the detection of an intensity-based stimulus but not when these stimuli were polarized. This study is the first to demonstrate that polarization vision reduces the negative impacts that dynamic illumination can have on visual perception.
| S-EPMC9462692 | biostudies-literature
Project description:It has been shown that transient single mitochondrial depolarizations, known as flickers, tend to occur randomly in space and time. On the other hand, many studies have shown that mitochondrial depolarization waves and whole-cell oscillations occur under oxidative stress. How single mitochondrial flickering events and whole-cell oscillations are mechanistically linked remains unclear. In this study, we developed a Markov model of the inner membrane anion channel in which reactive-oxidative-species (ROS)-induced opening of the inner membrane anion channel causes transient mitochondrial depolarizations in a single mitochondrion that occur in a nonperiodic manner, simulating flickering. We then coupled the individual mitochondria into a network, in which flickers occur randomly and sparsely when a small number of mitochondria are in the state of high superoxide production. As the number of mitochondria in the high-superoxide-production state increases, short-lived or abortive waves due to ROS-induced ROS release coexist with flickers. When the number of mitochondria in the high-superoxide-production state reaches a critical number, recurring propagating waves are observed. The origins of the waves occur randomly in space and are self-organized as a consequence of random flickering and local synchronization. We show that at this critical state, the depolarization clusters exhibit a power-law distribution, a signature of self-organized criticality. In addition, the whole-cell mitochondrial membrane potential changes from exhibiting small random fluctuations to more periodic oscillations as the superoxide production rate increases. These simulation results may provide mechanistic insight into the transition from random mitochondrial flickering to the waves and whole-cell oscillations observed in many experimental studies.
| S-EPMC3207179 | biostudies-literature
Project description:BACKGROUND:Bright light at night is known to suppress melatonin secretion. Novel photoreceptors named intrinsically photosensitive retinal ganglion cells (ipRGCs) are mainly responsible for projecting dark/bright information to the suprachiasmatic nucleus and thus regulating the circadian system. However, it has been shown that the amplitude of the electroretinogram of ipRGCs is considerably lower under flickering light at 100 Hz than at 1-5 Hz, suggesting that flickering light may also affect the circadian system. Therefore, in this study, we evaluated light-induced melatonin suppression under flickering and non-flickering light. METHODS:Twelve male participants between the ages of 20 and 23 years (mean?±?S.D.?=?21.6?±?1.5 years) were exposed to three light conditions (dim, 100-Hz flickering, and non-flickering blue light) from 1:00 A.M. to 2:30 A.M., and saliva samples were obtained just before 1:00 A.M. and at 1:15, 1:30, 2:00, and 2:30 A.M. RESULTS:A repeated measures t test with Bonferroni correction showed that at 1:15 A.M., melatonin concentrations were significantly lower following exposure to non-flickering light compared with dim light, whereas there was no significant difference between the dim and 100-Hz flickering light conditions. By contrast, after 1:30 A.M., the mean melatonin concentrations were significantly lower under both 100-Hz flickering and non-flickering light than under dim light. CONCLUSION:Although melatonin suppression rate tended to be lower under 100-Hz flickering light than under non-flickering light at the initial 15 min of the light exposure, the present study suggests that 100-Hz flickering light may have the same impact on melatonin secretion as non-flickering light.
| S-EPMC6194675 | biostudies-other
Project description:Tourette syndrome (TS) is a neuropsychiatric disorder characterized by the occurrence of vocal and motor tics. Tics are involuntary, repetitive movements and vocalizations that occur in bouts, typically many times in a single day, and are often preceded by a strong urge-to-tic-referred to as a premonitory urge (PU). TS is associated with the following: dysfunction within cortical-striatal-thalamic-cortical (CSTC) brain circuits implicated in the selection of movements, impaired operation of GABA signaling within the striatum, and hyper-excitability of cortical sensorimotor regions that might contribute to the occurrence of tics. Non-invasive brain stimulation delivered to cortical motor areas can modulate cortical motor excitability, entrain brain oscillations, and reduce tics in TS. However, these techniques are not optimal for treatment outside of the clinic. We investigated whether rhythmic pulses of median nerve stimulation (MNS) could entrain brain oscillations linked to the suppression of movement and influence the initiation of tics in TS. We demonstrate that pulse trains of rhythmic MNS, delivered at 12 Hz, entrain sensorimotor mu-band oscillations, whereas pulse trains of arrhythmic MNS do not. Furthermore, we demonstrate that although rhythmic mu stimulation has statistically significant but small effects on the initiation of volitional movements and no discernable effect on performance of an attentionally demanding cognitive task, it nonetheless leads to a large reduction in tic frequency and tic intensity in individuals with TS. This approach has considerable potential, in our view, to be developed into a therapeutic device suitable for use outside of the clinic to suppress tics and PU in TS.
| S-EPMC7308804 | biostudies-literature
Project description:BackgroundThe selection of optimal deep brain stimulation (DBS) parameters is time-consuming, experience-dependent, and best suited when acute effects of stimulation can be observed (e.g., tremor reduction).ObjectivesTo test the hypothesis that optimal stimulation location can be estimated based on the cortical connections of DBS contacts.MethodsWe analyzed a cohort of 38 patients with Parkinson's disease (24 training, and 14 test cohort). Using whole-brain probabilistic tractography, we first mapped the cortical regions associated with stimulation-induced efficacy (rigidity, bradykinesia, and tremor improvement) and side effects (paresthesia, motor contractions, and visual disturbances). We then trained a support vector machine classifier to categorize DBS contacts into efficacious, defined by a therapeutic window ≥2 V (threshold for side effect minus threshold for efficacy), based on their connections with cortical regions associated with efficacy versus side effects. The connectivity-based classifications were then compared with actual stimulation contacts using receiver-operating characteristics (ROC) curves.ResultsUnique cortical clusters were associated with stimulation-induced efficacy and side effects. In the training dataset, 42 of the 47 stimulation contacts were accurately classified as efficacious, with a therapeutic window of ≥3 V in 31 (66%) and between 2 and 2.9 V in 11 (24%) electrodes. This connectivity-based estimation was successfully replicated in the test cohort with similar accuracy (area under ROC = 0.83).ConclusionsCortical connections can predict the efficacy of DBS contacts and potentially facilitate DBS programming. The clinical utility of this paradigm in optimizing DBS outcomes should be prospectively tested, especially for directional electrodes.
| S-EPMC6649384 | biostudies-literature
Project description:The glymphatic-lymphatic system is increasingly recognized as fundamental for the homeostasis of the brain milieu since it defines cerebral spinal fluid flow in the brain parenchyma and eliminates metabolic waste. Animal and human studies have uncovered several important physiological factors regulating the glymphatic system including sleep, aquaporin-4, and hemodynamic factors. Yet, our understanding of the modulation of the glymphatic system is limited, which has hindered the development of glymphatic-based treatment for aging and neurodegenerative disorders. Here, we present the evidence from fluorescence tracing, two-photon recording, and dynamic contrast-enhanced magnetic resonance imaging analyses that 40 Hz light flickering enhanced glymphatic influx and efflux independently of anesthesia and sleep, an effect attributed to increased astrocytic aquaporin-4 polarization and enhanced vasomotion. Adenosine-A2A receptor (A2AR) signaling emerged as the neurochemical underpinning of 40 Hz flickering-induced enhancement of glymphatic flow, based on increased cerebrofluid adenosine levels, the abolishment of enhanced glymphatic flow by pharmacological or genetic inactivation of equilibrative nucleotide transporters-2 or of A2AR, and by the physical and functional A2AR-aquaporin-4 interaction in astrocytes. These findings establish 40 Hz light flickering as a novel non-invasive strategy of enhanced glymphatic flow, with translational potential to relieve brain disorders.
| S-EPMC11300858 | biostudies-literature