Flickering Red-Light Stimulus for Promoting Coherent 40 Hz Neural Oscillation: A Feasibility Study

An Integrative Review of Brainwave Entrainment Benefits for Human Health

Brainwave Entrainment (BWE) is a noninvasive method of neuromodulation based on the principle that auditory or visual stimulation at a specific frequency can lead the brain's electrocortical activity to oscillate at the frequency of the external signal or its multiples. This phenomenon could be used to alter physiological and psychological states. Therefore, we conducted an integrative review to answer the question: "What are the observed benefits of BWE on human health and well-being?" We searched for studies published in the last ten years in the Directory of Open Access Journals (DOAJ), EMBASE, Virtual Health Library (BVS), PubMed, SciELO, and Cochrane Library databases in April 2024. Searches were conducted in English, Portuguese, and Spanish. A total of 84 studies were included in our review. Studies showed improvements in various conditions, such as pain, sleep disturbances, mood disorders, cognition, and neurodegenerative disorders. In conclusion, our findings align with previous reviews and underscore the need for further research on BWE, particularly with larger sample sizes, robust control groups, and randomized clinical trial designs. Nevertheless, BWE demonstrates promising therapeutic potential and may support the management of various health conditions, enhancing individuals' quality of life.

High-gamma frequency flash stimulation as a possible cognitive facilitator in rat pups

High-gamma frequency flashes can enhance cognition by synchronizing neural oscillations in mammals. Early flash treatment promotes the development of improved cognitive functions in young children. However, it is unclear whether exposure to high-gamma frequency flashes in preschool-aged individuals affects cognition in preadolescents by regulating neural oscillations in the brain. Here, we aimed to investigate the effects of gamma-frequency flashes on cognitive ability. In this study, the effect of high-frequency flicker on cognitive performance was verified by behavioural experiments such as the open-field test and the water maze, but also proteomics. We found that external 40 Hz and 70 Hz frequency flashes synchronized neural oscillations at the corresponding frequencies in the primary visual cortex (V1) of rats. Rats that underwent 70 Hz flash intervention had better cognitive behavioural performance in the early stages of training. The 70 Hz flash frequency upregulated proteins associated with neuronal growth and differentiation, such as Snapin, FoxO3, Hspa12a, and Penk, and activated the MAPK signalling pathway, signalling pathway regulating stem cell pluripotency, and the neuroactive ligand-receptor interaction pathway. These proteins and pathways play important roles in cognitive functions. Our study revealed that 70 Hz flashes received by young children early in their development substantially promote the growth of cognitive capabilities in the brain. Exposure to 70 Hz flashes may be a new intervention method and a new strategy for improving cognition.

Acousto-optic stimuli to promote coherent 40-Hz frequency entrainment effect

BACKGROUND

 Research has shown that a fundamental frequency of 40 Hz in continuous neural oscillation is indicative of normal brain activity; in Alzheimer disease (AD) patients, these oscillations either disappear or are significantly interrupted. Research has also indicated that the degenerative impacts of AD in mice were mitigated by the synchronization of 40-Hz acousto-optic stimulation (AOS).

OBJECTIVE

 To examine the impact of employing a 40-Hz AOS intervention on the induction of a substantial 40-Hz frequency entrainment and improvement in working memory performance among a sample of young individuals in good health. We conduct an analysis of event-related potentials (ERPs) derived from electroencephalogram (EEG) data following the presentation of AOS.

METHODS

 We recruited 20 healthy volunteers (median age: 25 years; 8 female subjects). Following the administration of various stimuli, including no stimuli, 40-Hz AOS, pink noise, and 40Hz acoustic stimuli (AS), the participants were required to complete a working memory task. A total of 62 electrodes were used to record EEG data, which was subsequently analyzed to investigate the impact of AOS on the activity of working memory. We also aimed to determine if AOS lead to a more pronounced 40-Hz frequency entrainment.

RESULTS

 Following the administration of AOS, a notable enhancement in the 40-Hz power of pertinent cerebral areas was observed, accompanied by a substantial improvement in the performance of the subjects on working memory tests subsequent to the stimulation.

CONCLUSION

 The findings unequivocally establish the efficacy of using AOS to enhance the 40-Hz power and working memory.

The impact of wavelength on acute non-visual responses to light: A systematic review and meta-analysis

Light is detected in the eye by three classes of photoreceptors (rods, cones, and intrinsically photosensitive retinal ganglion cells (ipRGCs)) that are each optimized for a specific function and express a particular light-detecting photopigment. The significant role of short-wavelength light and ipRGCs in improving alertness has been well-established; however, few reviews have been undertaken to assess the other wavelengths' effects regarding timing and intensity. This study aims to evaluate the impact of different narrowband light wavelengths on subjective and objective alertness among the 36 studies included in this systematic review, 17 of which were meta-analyzed. Short-wavelength light (∼460-480 nm) significantly improves subjective alertness, cognitive function, and neurological brain activities at night, even for a sustained period (∼6h) (for λmax: 470/475 nm, 0.4 < |Hedges's g| < 0.6, p < 0.05), but except early morning, it almost does not show this effect during the day when melatonin level is lowest. Long-wavelength light (∼600-640 nm) has little effect at night, but significantly increases several measures of alertness at lower irradiance during the daytime (∼1h), particularly when there is homeostatic sleep drive (for λmax: ∼630 nm, 0.5 < |Hedges's g| < 0.8, p < 0.05). The results further suggest that melanopic illuminance may not always be sufficient to measure the alerting effect of light.

Circadian clocks, cognition, and Alzheimer's disease: synaptic mechanisms, signaling effectors, and chronotherapeutics

Modulation of basic biochemical and physiological processes by the circadian timing system is now recognized as a fundamental feature of all mammalian organ systems. Within the central nervous system, these clock-modulating effects are reflected in some of the most complex behavioral states including learning, memory, and mood. How the clock shapes these behavioral processes is only now beginning to be realized. In this review we describe recent findings regarding the complex set of cellular signaling events, including kinase pathways, gene networks, and synaptic circuits that are under the influence of the clock timing system and how this, in turn, shapes cognitive capacity over the circadian cycle. Further, we discuss the functional roles of the master circadian clock located in the suprachiasmatic nucleus, and peripheral oscillator populations within cortical and limbic circuits, in the gating of synaptic plasticity and memory over the circadian cycle. These findings are then used as the basis to discuss the connection between clock dysregulation and cognitive impairments resulting from Alzheimer's disease (AD). In addition, we discuss the conceptually novel idea that in AD, there is a selective disruption of circadian timing within cortical and limbic circuits, and that it is the disruption/desynchronization of these regions from the phase-entraining effects of the SCN that underlies aspects of the early- and mid-stage cognitive deficits in AD. Further, we discuss the prospect that the disruption of circadian timing in AD could produce a self-reinforcing feedback loop, where disruption of timing accelerates AD pathogenesis (e.g., amyloid deposition, oxidative stress and cell death) that in turn leads to a further disruption of the circadian timing system. Lastly, we address potential therapeutic approaches that could be used to strengthen cellular timing networks and, in turn, how these approaches could be used to improve cognitive capacity in Alzheimer's patients.

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.