Free-running sleep is a rare sleep pattern whereby the sleep schedule of a person shifts later every day. It occurs as the sleep disorder non-24-hour sleep–wake disorder or artificially as part of experiments used in the study of circadian and other rhythms in biology. Study subjects are shielded from all time cues, often by a constant light protocol, by a constant dark protocol or by the use of light/dark conditions to which the organism cannot entrain such as the ultrashort protocol of one hour dark and two hours light. Also, limited amounts of food may be made available at short intervals so as to avoid entrainment to mealtimes. Subjects are thus forced to live by their internal circadian "clocks".
Chronobiology is a field of biology that examines timing processes, including periodic (cyclic) phenomena in living organisms, such as their adaptation to solar- and lunar-related rhythms. These cycles are known as biological rhythms. Chronobiology comes from the ancient Greek χρόνος, and biology, which pertains to the study, or science, of life. The related terms chronomics and chronome have been used in some cases to describe either the molecular mechanisms involved in chronobiological phenomena or the more quantitative aspects of chronobiology, particularly where comparison of cycles between organisms is required.
The visual system comprises the sensory organ and parts of the central nervous system which gives organisms the sense of sight as well as enabling the formation of several non-image photo response functions. It detects and interprets information from the optical spectrum perceptible to that species to "build a representation" of the surrounding environment. The visual system carries out a number of complex tasks, including the reception of light and the formation of monocular neural representations, colour vision, the neural mechanisms underlying stereopsis and assessment of distances to and between objects, the identification of a particular object of interest, motion perception, the analysis and integration of visual information, pattern recognition, accurate motor coordination under visual guidance, and more. The neuropsychological side of visual information processing is known as visual perception, an abnormality of which is called visual impairment, and a complete absence of which is called blindness. Non-image forming visual functions, independent of visual perception, include the pupillary light reflex and circadian photoentrainment.
A photoreceptor cell is a specialized type of neuroepithelial cell found in the retina that is capable of visual phototransduction. The great biological importance of photoreceptors is that they convert light into signals that can stimulate biological processes. To be more specific, photoreceptor proteins in the cell absorb photons, triggering a change in the cell's membrane potential.
The suprachiasmatic nucleus or nuclei (SCN) is a small region of the brain in the hypothalamus, situated directly above the optic chiasm. It is the principal circadian pacemaker in mammals and is necessary for generating circadian rhythms. Reception of light inputs from photosensitive retinal ganglion cells allow the SCN to coordinate the subordinate cellular clocks of the body and entrain to the environment. The neuronal and hormonal activities it generates regulate many different body functions in an approximately 24-hour cycle.
CREB-TF is a cellular transcription factor. It binds to certain DNA sequences called cAMP response elements (CRE), thereby increasing or decreasing the transcription of the genes. CREB was first described in 1987 as a cAMP-responsive transcription factor regulating the somatostatin gene.
A retinal ganglion cell (RGC) is a type of neuron located near the inner surface of the retina of the eye. It receives visual information from photoreceptors via two intermediate neuron types: bipolar cells and retina amacrine cells. Retina amacrine cells, particularly narrow field cells, are important for creating functional subunits within the ganglion cell layer and making it so that ganglion cells can observe a small dot moving a small distance. Retinal ganglion cells collectively transmit image-forming and non-image forming visual information from the retina in the form of action potential to several regions in the thalamus, hypothalamus, and mesencephalon, or midbrain.
Melanopsin is a type of photopigment belonging to a larger family of light-sensitive retinal proteins called opsins and encoded by the gene Opn4. In the mammalian retina, there are two additional categories of opsins, both involved in the formation of visual images: rhodopsin and photopsin in the rod and cone photoreceptor cells, respectively.
Intrinsically photosensitive retinal ganglion cells (ipRGCs), also called photosensitive retinal ganglion cells (pRGC), or melanopsin-containing retinal ganglion cells (mRGCs), are a type of neuron in the retina of the mammalian eye. The presence of ipRGCs was first suspected in 1927 when rodless, coneless mice still responded to a light stimulus through pupil constriction, This implied that rods and cones are not the only light-sensitive neurons in the retina. Yet research on these cells did not advance until the 1980s. Recent research has shown that these retinal ganglion cells, unlike other retinal ganglion cells, are intrinsically photosensitive due to the presence of melanopsin, a light-sensitive protein. Therefore, they constitute a third class of photoreceptors, in addition to rod and cone cells.
Ignacio Provencio is an American neuroscientist and the discoverer of melanopsin, an opsin found in specialized photosensitive ganglion cells of the mammalian retina. Provencio served as the program committee chair of the Society for Research on Biological Rhythms from 2008 to 2010.
The visual cycle is a process in the retina that replenishes the molecule retinal for its use in vision. Retinal is the chromophore of most visual opsins, meaning it captures the photons to begin the phototransduction cascade. When the photon is absorbed, the 11-cis retinal photoisomerizes into all-trans retinal as it is ejected from the opsin protein. Each molecule of retinal must travel from the photoreceptor cell to the RPE and back in order to be refreshed and combined with another opsin. This closed enzymatic pathway of 11-cis retinal is sometimes called Wald's visual cycle after George Wald (1906–1997), who received the Nobel Prize in 1967 for his work towards its discovery.
Light effects on circadian rhythm are the effects that light has on circadian rhythm.
Mammals normally have a pair of eyes. Although mammalian vision is not so excellent as bird vision, it is at least dichromatic for most of mammalian species, with certain families possessing a trichromatic color perception.
Russell Grant Foster, CBE, FRS FMedSci is a British professor of circadian neuroscience, the Director of the Nuffield Laboratory of Ophthalmology and the Head of the Sleep and Circadian Neuroscience Institute (SCNi). He is also a Nicholas Kurti Senior Fellow at Brasenose College at the University of Oxford. Foster and his group are credited with key contributions to the discovery of the non-rod, non-cone, photosensitive retinal ganglion cells (pRGCs) in the mammalian retina which provide input to the circadian rhythm system. He has written and co-authored over a hundred scientific publications.
Samer Hattar is a chronobiologist and a leader in the field of non-image forming photoreception. He is the Chief of the Section on Light and Circadian Rhythms at the National Institute of Mental Health, part of the National Institutes of Health. He was previously an associate professor in the Department of Neuroscience and the Department of Biology at Johns Hopkins University in Baltimore, MD. He is best known for his investigation into the role of melanopsin and intrinsically photosensitive retinal ganglion cells (ipRGC) in the entrainment of circadian rhythms.
Arnold Eskin was a professor of chronobiology at the University of Houston in Houston, Texas. He attended Vanderbilt University, where he received a degree in physics. He later attended University of Texas at Austin, where he received his Ph.D. in zoology in 1969. He is recognized in the term Eskinogram, and has been a leader in the discovery of mechanisms underlying entrainment of circadian clocks.
Robert Y. Moore is an American neurologist with interests in disorders of biological rhythms, movement disorders, and behavioral neurology. He is credited with discovering the function of the suprachiasmatic nucleus (SCN) as the circadian clock, as well as, describing its organization. He is also credited with establishing the role of the mammalian retinohypothalamic tract (RHT) as a photic entrainment pathway. Moore cin 2017 serves as a professor of neurology, with a secondary in psychiatry and neuroscience at the University of Pittsburgh, and as co-director of the National Parkinson Foundation Center of Excellence at the University of Pittsburgh.
Johanna H. Meijer is a Dutch scientist who has contributed significantly to the field of chronobiology. Meijer has made notable contributions to the understanding of the neural and molecular mechanisms of circadian pacemakers. She is known for her extensive studies of photic and non-photic effects on the mammalian circadian clocks. Notably, Meijer is the 2016 recipient of the Aschoff and Honma Prize, one of the most prestigious international prizes in the circadian research field. In addition to still unraveling neuronal mechanisms of circadian clocks and their applications to health, Meijer's lab now studies the effects of modern lifestyles on our circadian rhythm and bodily functions.
Tiffany M. Schmidt is an American researcher and chronobiologist, currently working as an Associate Professor of Neurobiology at Northwestern University. Schmidt, who works in Evanston, Illinois, studies the role of retinal ganglion cells (RGC) to determine how light can affect behavior, hormonal changes, vision, sleep, and circadian entrainment.
Russell Van Gelder is an American clinician-scientist and a board-certified ophthalmologist. He is most known for his work in the mechanisms of uveitis disease, his research on non-visual photoreception in the eye, and on vision-restoration methods for retinal degenerative disease.
