About this Research Topic
With rapid advances in solid-state lighting technology we can now control the temporal, intensity, and spectral characteristics of light exposure with exquisite precision. As per-capita consumption of electric lighting grows, this also creates novel light-exposure patterns in daily life such as through transient viewing of digital screens at night. However, our understanding of the circadian system’s photosensitivity and response characteristics has not kept up with this evolution in lighting technology nor environmental light exposure. For example, our understanding of light exposure induced circadian phase resetting, and the clinical phototherapy practices derived from that understanding, has largely been from experiments employing long-duration, steady-pattern, broad-spectrum stimuli.
Emerging evidence suggests that intermittent, short-duration light has similar efficacy as conventional lighting for circadian phase resetting. These preliminary findings question our knowledge of what factors should characterize a photic stimulus “dose” and challenge single-dimensional metrics that are typically used to describe light, such as intensity or duration. As the scientific community is only just beginning to investigate these responses and underlying mechanisms, we aim to bring together a focused group of scientists to explore and communicate the basic physiology mediating these responses and their translation to clinical practice within the home and bedroom. Special interests include novel phototherapy techniques such as light stimulation during sleep, and delivery optimization based on data from wearables and IoT based built environment sensing. We will also explore the understudied potential of prolonged periods of darkness—effectively the other component of intermittent light—to treat various neurologic and psychiatric disorders. Where possible, we will attempt to contextualize the opportunities afforded by light therapy compared/contrasted to other forms of neurostimulation with, for instance, sound or odor.
This Research Topic will draw on recent and ongoing research suggesting that our current understanding of the nonimage forming (NIF) system’s response to discrete light is inadequate to explain NIF responses to intermittent light exposure. The latest research shows that NIF responses to both ultra-short-duration exposure—flashes on timescales from nanoseconds to seconds—and longer transient patterns intercut with periods of darkness are robust and larger than expected based on our current understanding of NIF responses to uninterrupted light administration. These novel discoveries underscore the importance of further systematic examination of the persistent effects of brief, transient photo stimulation of the NIF system and the potential desensitization mechanisms that are prompted by prolonged visual contact with light. A better understanding of these mechanisms will help optimize light-based interventions to rehabilitate or enhance neurological and behavioral functions such as cognition (memory), affect, and recovery after stroke in normative and clinical populations.
This Research Topic will provide an overview of the concept and historical context surrounding intermittent light administration, its circadian physiology (and pathophysiology), and possible applications. Topic coverage will include:
• Review of the Circadian Literature on Light Fractionation and Flash Exposure;
• Does Art Imitate Time? Parallels between the Visual and Non-Image Forming Systems;
• Flash Induction of the Non-Image Forming System: At the Crossroads of Rods, Cones, and ipRGCs;
• Temporal Sensitivity of ‘Canonical’ Visual Responses;
• Comparative Neurology of Circadian Photoreception: From the Eye to the Clock;
• The Effects of Intermittent Light Exposure on Melatonin Suppression and Alertness;
• Mathematical/Computational Modeling of the NIF system’s Integration of Light;
• Mathematical/Computational Modeling of the Visual System’s Perception of Intermittent Light;
• Use of LED Technology in the Built Environment: Redesigning the Bedroom for Non-Invasive Phototherapy during Sleep;
• Use of Smart Lenses and Other Personal Wearable Technologies: Flash Codes, Hardware, and Biofeedback;
• Neurostimulation and Sleep: Where does Light Fit In?
• Phototherapeutic Approaches for Psychiatric and Neurological Disorders;
• Can Non-invasive Phototherapy Improve Sleep-Dependent Consolidation of Memory?
• The Dark Side of Intermittent Light: Potential Applications of Acute and Extended Periods of Darkness to Treat Clinical Disorders.
Keywords: Light, Flash, Intermittent, Circadian, Photo-stimulation
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