Advances in research on the effects of light on brain function
Release date: 2018-01-26 Source: Zhongzhao.com Share: 
introduction
Most of the behavioral and physiological phenomena in humans and other mammals have endogenous circadian rhythms such as consciousness, blood pressure, heart rate, respiration, body temperature, immune and neuroendothelial activity, and even cell division, which are natural choices and long-term moments. Adaptive features preserved in the evolutionary process. In the long-term evolution process, the biological body also developed a special structure - a circadian clock to harmonize the circadian rhythm of the above physiological activities. The light rhythm, as the most important feature of the periodic changes of the Earth's day and night environment, is the most important factor affecting the biological clock rhythm. Changes in lighting conditions are transmitted through the visual pathway to the circadian clock structure in the brain to adjust the rhythm of the physiology and behavior. With the deepening of the study, light can also affect brain function and cognition through non-visual pathways. This article will summarize the development of illumination on the regulation of the biological clock rhythm and the impact on the function of the brain. It is expected to be based on the application of photobiological and photochemical applications, environmental illumination engineering design and related disease prevention and clinical treatment.
1 illumination and biological clock rhythm
When exposed to light, the circadian clock system initiates a chain expansion process from light signals to nerve excretion signals, thereby conditioning most of the behavior and physiological activities of the organism. The photoreceptor on the retinal ganglion cells is the most direct light-receiving receptor, and then transmits the optical information to the main circadian clock of humans and other mammals through the subretinal hypothalamic bundle, ie, the hypothalamic anterior interstitial nucleus (Suprachiasmatic nuclei, SCN). As a central pacemaker (or oscillator) for the circadian cycle, SCN regulates a variety of physiological processes associated with light. After the SCN is exposed to light information, the expression of the clock gene and clock protein of the SCN neurons is stimulated. Nowadays, mammals have identified several clock-related genes, such as period gene, cryptochrome gene, bmall1, timeless, clock, Rev-Erbα and so on. There are four primary clock proteins, the agonist proteins CLOCK and BMAL1, the barrier proteins PER and CRY. CLOCK and BMAL1 form a dimer in the cytoplasm of SCN neurons, transport them into the nucleus, and bind to the gene regulatory region to activate transcription of target genes including per and cry. However, the expression of per and cry has a negative reflex regulation mechanism, that is, the PER:CRY protein constitutes a heterodimer transported into the nucleus through the CLOCK:BMAL1 polymer effect and the transcription of æºper and cry. When the PER:CRY protein is degraded by the ubiquitin-dependent signaling pathway, the CLOCK:BMAL1 polymer is released and the above cycle is mobilized from the hair. In addition, ROR and its negative regulator REV-ERBα have also been found to be clock proteins for ensuring the accuracy of circadian rhythms. The autonomous transcription and translational conditioning reverberation loops formed by these genes and protein products are the molecular mechanisms underlying the regulation of the circadian clock.
The molecular mechanism of illumination through the biological clock also affects the function of SCN, primarily the spontaneous action potential of SCN neurons. Under light conditions (daytime), the discharge frequency is the highest (6 to 10 Hz), and in the black environment (at night), the discharge frequency is lower (<1 Hz). In the meantime, the Per1 activator activity has a positive correlation with the SCN neuron firing frequency, and it is clarified that Per1 may be the key clock gene for light-affecting SCN discharge [3-4].
Illumination through SCN regulates the rhythm of behavioral, physiological, metabolic, and hormonal excretion. There are three primary pathways: 1) the medullary pathway of the medial preoptic area, extending into the paraventricular nucleus of the thalamus (transmitting the SCN signal to the medial prefrontal cortex); ) traversing the area along the bottom of the brain and entering the ventral medial nucleus; 3) announcing the end of the SCN along the dorsal and posterior end of the arc, the ventral subparaventricular zone (vSPZ) and the hypothalamic ventricle The ventral region of the paraventricular hypothalamic nucleus (PVN) and the dorsolateral compartment of the dorsal ventricle are the largest of the three pathways. SPZ is an important relay station for SCN signals, regulating sleep rhythm, body temperature, spontaneous activity and nerve activity.
The forebrain is also a brain region that has important conditioning effects on mammalian rhythmic behavior. In the forebrain, NPAS2 (neuronal PAS domain protein 2, also known as MOP4) replaces CLOCK and BMAL1 to form a polymer, which initiates the molecular clock mechanism. It has been shown that the forebrain and the SCN region can also regulate the behavioral rhythm of the organism according to signals such as ambient light. In addition to the central diurnal oscillator, peripheral organs also have a peripheral oscillator that expresses one or more clock genes, but the peripheral oscillator is centrally regulated. Illumination indirectly regulates the peripheral oscillator, induces sympathetic excitation, and parasympathetic nerve press, resulting in elevated blood pressure, accelerated heart rate, and weakened gastrointestinal activity.
The light signal can also regulate the synthesis and excretion of melatonin (MEL) through the pineal gland (PG). Although the onset and persistence of circadian rhythm by MEL in humans and other mammals is not necessary now, it can regulate the light sensitivity of SCN and the frequency of neuronal firing through the receptor binding to SCN to participate in the regulation of circadian rhythm. . Together as an intra-muscular excretion transducer, it can transmit the external photoperiod signal more usefully in the form of circadian rhythm to the central nervous system, intestine, liver, kidney, gonads and other arrangements and organs, with immunomodulation, anti-tumor, anti- Aging, reproductive conditioning and other functions.
2 effects of light on brain function
2.1 Illumination affects human sleep through circadian rhythm
The most direct effect of light on the human and other mammalian brain functions is the circadian rhythm of sleep and enlightenment. In the process of evolution, humans or animals have formed an endogenous free running period, such as the endogenous rhythm of humans for nearly 25 h, while the endogenous rhythm of mice is nearly 23 h. But when people are in the absence of light for 2 weeks, sleep/enlightenment will be contrary to the day and night. When a person is placed from the head under a 24h light-dark (LD) rhythm, the rhythm of the biological clock is set from the beginning to 24h with the rhythm of the ambient light. Abundant light can cause the SCN-driven rhythm to drift and change the sleep rhythm. This light-induced rhythm drift has been clearly defined as a right-to-error visual effect, as there is still a light response in mice lacking a photoreceptor, that is, light can induce phase drift of its biological clock rhythm and excretion of melatonin. Light can also be excreted by melatonin in the scorpion. The material basis of this non-visual response to light is primarily the substantia nigra, encoded by the gene Opn4. Light does not have the ability to regulate sleep in Opn4 knockout mice. Other photoreceptor nerve cells have also been found to have a non-visual responsiveness to light, participating in the conditioning of light to sleep. Unlike classical visual photoreceptors that are sensitive to green light (550 nm), light-sensitive nerve cells are sensitive to blue light (480 nm). Under blue light, melatonin excretion is affected by sputum, body temperature, heart rate, subjective sleepiness, and vigilance. The rhythm drift caused by light is a long-term process, but it has been shown to have an acute light effect in strong light, normal indoor light or even weak light, manifested in physiological changes such as hormone excretion, fatigue, and alertness to body temperature gene expression. Direct light can reduce EEG alpha (8-12 Hz), beta (20-30 Hz) and low frequency activity associated with sleep. Night lighting has become an important part of modern times, but night lights can disturb the rhythm of the endogenous biological clock, and the melatonin seizures and release, causing human sleep. Sleep disorders are closely related to many diseases such as depression and dementia. Therefore, in the lighting design of urban and family, not only the function of lighting, beauty, energy saving and environmental protection, but also the lighting design concept that is beneficial to human health will be the development direction of lighting engineering design.
2.2 The effect of lighting on mood
The effect of light on human mood has been proven. Abnormal light in the environment can lead to the onset of diseases such as emotional obstruction including depression. The discovery of this phenomenon originated from an emotional obstruction in the autumn and winter seasons, the relief of symptoms in spring and summer, and immediate emotional obstacles. Some scholars have classified it as a subtype of severe depression. The disease is high in high latitudes, and the reduction of light in autumn and winter is considered to be the primary cause of its disease. After artificial compensation, the symptoms can be alleviated. Many experimental studies have revealed the influence of illumination on emotions after changing the length of illumination: the addition of light can add animal movement behavior and improve its depressed behavior. Depressive disorder itself has differences in day and night changes in addition to seasonal differences. Sleep disorders are recognized as one of the leading symptoms of depression, and are also closely related to a range of mental health-related symptoms. Moderately slow sleep plundering after changing ambient lighting conditions is beneficial to improve emotional obstruction. The correlation between clock genes and mental disorders such as human emotional obstruction has been initially demonstrated. Cry2 gene and depression and two-way emotions impede genetic characteristics, Per3, Cry1, Tim gene and genetic characteristics of schizophrenia.
2.3 The effect of illumination on cognitive function
Light can affect cognition through direct activation effects. The relevant brain regions of direct light effects on brain cognitive function can be detected by positron emission tomography (PET) and functional magnetic resonance imaging (FMRI), which touch the brain stem The area around the hypothalamus, the hippocampus, the dorsolateral anterior cortex, and the left anterior cortex, which are related to long-term resilience and attention. A few minutes after exposure and exposure, video search, digital recall, addition and subtraction, etc. can be agilely enhanced. The wavelength of light is also necessarily related to brain cognition. For example, in the vigilance response test, the usefulness of human behavior must be higher under green light under blue light. This also indicates that light-sensitive nerve cells play a more important role in light-to-brain cognitive function conditioning [15-17]. Continued nighttime exposure and changes to sleep-conscious rhythm can alter the rhythm of cognitive changes and continue to illuminate cognitive functions. The experimental study showed that after a few weeks of stretching the rats' ambient light, the learning and recall of the rats can be significantly reduced, the mitochondria of the neurons are damaged, the synapses are reduced, and the beta-amyloid content of hippocampus is increased, and the phosphorylation of tau is enhanced. The pathogenesis of Alzheimer's disease.
2.4 The effect of illumination on spontaneous activity
The light rhythm affects a variety of neurological functions by conditioning the brain's neurotransmitter excretion. In the meantime, dopamine (DA), as a recognized neurotransmitter that regulates exercise, reward and learning, participates in rheumatoid regulation of multiple central brain regions such as retina, midbrain, striatum, thalamus and hippocampus. Parkinson's patients with substantia nigra DA neuron degeneration, DA reduction, not only cause stop tremor, muscle rigidity, slow movement and other motor symptoms, but also cause spontaneous activity changes, visual obstruction, sleep disorder, memory obstruction, olfactory loss and other circadian rhythms A variety of symptoms associated with it. It has been shown that light-mediated DA regulation of photoreceptor ganglion cells and damage to SCN pathways is one of the possible mechanisms by which decreased DA levels in PD patients affect spontaneous rhythm. However, the latest research by Fujita et al. showed that dopamine-deficient mice can adhere to normal light/black cycle-dependent autonomic activities, and clarify that there are other compensatory pathways in addition to DA to regulate spontaneous activities. Therefore, the mechanism of light through the regulation of nerve function such as autonomous activities needs further discussion.
3 Conclusion
Illumination is the primary influential factor in the circadian rhythm of humans and other mammals. With the deepening of the research on the molecular mechanism of the biological clock, the influence of illumination on the function of the living body, especially the human brain, becomes clearer. The above research indicates that natural and artificial light has made a certain development in the relevant areas of human brain sleep rhythm, mental health, and learning cognition. Illumination not only regulates human rhythmic behavior through visual pathways, but also affects brain function through many non-visual signals. The timing, wavelength, and intensity of light all affect the regulation of brain function. Today, with the rapid development of science and technology, it is urgent to clarify the molecular mechanism of illumination on circadian rhythm and mood, cognition and other brain functions. On the one hand, it provides counseling for the diagnosis and treatment of various diseases such as depression, Parkinson's disease and Alzheimer's disease. It has important clinical significance; on the other hand, it is a reference for the search for a more comprehensive and accurate response to the biosafety of lighting design. This is also a manifestation of people's high concern for photobiosafety, from the perspective of human health. Lighting industry design raises higher requirements.
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