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The Sleeping Brain
Published in Hanno W. Kirk, Restoring the Brain, 2020
Incident light upon the retinae constitutes the main stimulus or time giver (Zeitgeber) that controls the circadian rhythm. Under normal circumstances, early morning light exposure sends impulses from the retinae via the retinohypothalamic tract (RHT)3 to the SCN, which then resets itself – much as setting a mechanical watch daily keeps it running on time. The SCN may be viewed as something of a toggle switch that sets in motion the cyclic activity of specific wake-promoting and sleep-promoting neurons. The SCN has greater activity during the day compared to night. Targets of SCN activity are involved in modulating highly diverse activities, including autonomic and neuroendocrine function as well as sensorimotor integration and affective processes. Output of a portion of the SCN also controls the timing of melatonin release, which itself is central to bringing about sleep onset through negative feedback on the SCN.4 Light inhibits melatonin production. (See Figure 14.2)
The Pineal Gland and Melatonin
Published in George H. Gass, Harold M. Kaplan, Handbook of Endocrinology, 2020
Jerry Vriend, Nancy A.M. Alexiuk
The retinohypothalamic tract to the SCN is important in the entrainment of visually dependent circadian rhythms. Another tract, with terminations in the SCN, is the geniculo-hypothalamic tract (GHT), a secondary visual projection which may participate in entrainment of circadian rhythms.118,119 The intergeniculate leaflet, which is the source of the GHT, also, according to recent reports, projects directly to the pineal gland in the rat and gerbil.120,121 However, any functional role it may have in providing light information to the pineal gland does not appear to have been investigated. Parasympathetic innervation of pinealocytes is not considered to be of major importance in mammals.107 Parasympathetic fibers, however, have been reported in the monkey and in the rabbit.122,123 The parasympathetic innervation of the pineal in mammals originates from perikarya in the pterygopalatine ganglia.124 Cholinergic receptors have been demonstrated in the rat pineal.125 Pharmacological studies have shown parasympathetic effects on indole metabolism in the pineal but little influence on melatonin production.126 Ganglion cells have been observed in primates,127 rabbits,123,128 and the ferret.129,130 The relationship of the ganglion cells to other autonomic fibers is not clear.
Consciousness, Sleep and Hypnosis, Meditation, and Psychoactive Drugs
Published in Mohamed Ahmed Abd El-Hay, Understanding Psychology for Medicine and Nursing, 2019
In humans and mammals, the circadian rhythms are controlled by a tiny cluster of neurons in the medial hypothalamus called the suprachiasmatic nucleus (SCN), i.e., the master clock (Moore, 2007). Damage to the SCN in rats abolished their circadian rhythms of temperature, cortisol secretion, eating, drinking, and sleep–wakefulness. Keeping the circadian rhythms synchronized with one another and on a 24-hour schedule is also controlled by environmental time cues. The most important of these cues is bright light, especially sunlight. Light is detected by photoreceptors in the eye, and is communicated via the visual system to the SCN (which lies above the optic chiasm) in the hypothalamus (Berson, Dunn, & Takao, 2002; Drouyer, Rieux, Hut, & Cooper, 2007). A tuft of nerve fibers branches off from the main nerve and penetrates the hypothalamus above, forming synaptic connections with cells in the SCN. This pathway (the retinohypothalamic tract) allows a link between the outside world and the brain’s own clock (Blakemore, 1988). Information regarding light is also conveyed to the SCN indirectly through the intergeniculate leaflet of the lateral geniculate body.
Impaired biological rhythm in men with methamphetamine use disorder: the relationship with sleep quality and depression
Published in Journal of Substance Use, 2023
Chronobiology is concerned with the timing of biological events, particularly repetitive or cyclical events, in organisms. Circadian rhythm refers to biological variations or rhythms with a cycle of approximately 24 hours (Vitaterna et al., 2001). The most widely used biological rhythm is the circadian rhythm. Although the circadian system in humans consists of the suprachiasmatic nucleus (SCN), retina, pineal gland and retinohypothalamic tract, the center responsible for the circadian rhythm is the SCN located in the anterior hypothalamus, also known as the biological clock. The circadian rhythm is primarily synchronized by light. Apart from light, it is also regulated by social rhythm givers (Social Zeitgeber). These are social factors, such as the hours when social interactions, work, exercise, bedtime and wake-up times, and meals occur (Selvi et al., 2011a).
Daytime and season do not affect reinforcement learning capacity in a response time adjustment task
Published in Chronobiology International, 2021
Sina Kohne, Luise Reimers, Malika Müller, Esther K. Diekhof
The circadian clock system follows an approximately 24 hours-rhythm. It is regulated by zeitgeber, mainly photic signals (natural and artificial light), and possibly by other stimuli such as temperature, humidity or physical activity (Boivin & Boudreau 2014; Meyer et al. 2016). Controlled by clock genes located in the suprachiasmatic nucleus as the primary pacemaker and various other tissues, the circadian rhythm is sustained using intracellular feedback loops. Variations in light disposability based on the day–night rhythm are detected by retinal ganglion cells. These cells enable photic entrainment via the retinohypothalamic tract to the suprachiasmatic nucleus (Berson et al. 2002). The procedure allows indirect measurement of day length via photic signals managed by melatonin. This processing is essential for behavioral adaptions.
Thermal lesions of the SCN do not abolish all gene expression rhythms in rat white adipose tissue, NAMPT remains rhythmic
Published in Chronobiology International, 2021
Rianne Van Der Spek, Ewout Foppen, Eric Fliers, Susanne La Fleur, Andries Kalsbeek
The circadian timing system coordinates physiology and behavior and enables an organism to anticipate recurring events during the day-night cycle. In mammals, a molecular clock is found in nearly every cell, consisting of a network of transcriptional translational auto-regulatory feedback loops (TTFL) (recently reviewed in (Takahashi 2017). The ‘central pacemaker’ or ‘master clock’ in the mammalian brain resides in the suprachiasmatic nucleus (SCN), a bilateral nucleus in the anterior hypothalamus, located just above the optic chiasm. Its endogenously generated circadian rhythm is synchronized to the exact 24 h rhythm of the external light-dark (LD) cycle by photic input from the retina via the retinohypothalamic tract (RHT) (Canteras et al. 2011). Although photic input is the main stimulus for synchronizing the SCN to the external environment, information from many other time cues, such as locomotor activity and arousal, variation in body temperature, local energy availability, circulating nutrients and hormones, as well as social signals contribute to this process. The SCN then uses various signaling pathways to relay this integrated temporal information to the ‘peripheral clocks’ in other brain areas and in the rest of the body (Albrecht 2012; Asher and Schibler 2011; Mohawk et al. 2012).