![Biological clock human](https://upload.wikimedia.org/wikipedia/commons/5/5f/Biological_clock_human.PNG)
Chronobiology is a field of
biology
Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process hereditary i ...
that examines
timing processes, including periodic (cyclic) phenomena in living organisms, such as their adaptation to
solar- and
lunar
Lunar most commonly means "of or relating to the Moon".
Lunar may also refer to:
Arts and entertainment
* ''Lunar'' (series), a series of video games
* "Lunar" (song), by David Guetta
* "Lunar", a song by Priestess from the 2009 album ''Prior t ...
-related rhythms.
These cycles are known as biological rhythms. Chronobiology comes from the ancient Greek
χρόνος (''chrónos'', meaning "time"), and
biology
Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process hereditary i ...
, which pertains to the study, or science, of
life
Life is a quality that distinguishes matter that has biological processes, such as signaling and self-sustaining processes, from that which does not, and is defined by the capacity for growth, reaction to stimuli, metabolism, energ ...
. 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.
Chronobiological studies include but are not limited to comparative
anatomy
Anatomy () is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science that deals with the structural organization of living things. It is an old science, having its ...
,
physiology
Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemical ...
,
genetics
Genetics is the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) It is an important branch in biology because heredity is vital to organisms' evolution. Gregor Mendel, a Moravian Augustinian friar wor ...
,
molecular biology
Molecular biology is the branch of biology that seeks to understand the molecular basis of biological activity in and between cells, including biomolecular synthesis, modification, mechanisms, and interactions. The study of chemical and physi ...
and
behavior of organisms related to their
biological rhythm
Biological rhythms are repetitive biological processes. Some types of biological rhythms have been described as biological clocks. They can range in frequency from microseconds to less than one repetitive event per decade. Biological rhythms are st ...
s.
Other aspects include
epigenetics
In biology, epigenetics is the study of stable phenotypic changes (known as ''marks'') that do not involve alterations in the DNA sequence. The Greek prefix '' epi-'' ( "over, outside of, around") in ''epigenetics'' implies features that are "o ...
, development, reproduction, ecology and evolution.
The subject
Chronobiology studies variations of the timing and duration of biological activity in living organisms which occur for many essential biological processes. These occur (a) in animals (eating, sleeping, mating, hibernating, migration, cellular regeneration, etc.), (b) in plants (leaf movements,
photosynthetic reactions, etc.), and in microbial organisms such as fungi and protozoa. They have even been found in
bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...
, especially among the
cyanobacteria
Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blu ...
(aka blue-green algae, see
bacterial circadian rhythms Bacterial circadian rhythms, like other circadian rhythms, are endogenous "biological clocks" that have the following three characteristics: (a) in constant conditions (i.e. constant temperature and either constant light or constant darkness ) they ...
). The best studied rhythm in chronobiology is the
circadian rhythm, a roughly 24-hour cycle shown by physiological processes in all these organisms. The term ''circadian'' comes from the
Latin
Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
''circa'', meaning "around" and ''dies'', "day", meaning "approximately a day." It is regulated by
circadian clock
A circadian clock, or circadian oscillator, is a biochemical oscillator that cycles with a stable phase (waves), phase and is synchronized with solar time.
Such a clock's ''in vivo'' period is necessarily almost exactly 24 hours (the earth's curre ...
s.
The circadian rhythm can further be broken down into routine cycles during the 24-hour day:
*
Diurnal, which describes organisms active during daytime
*
Nocturnal, which describes organisms active in the night
*
Crepuscular, which describes animals primarily active during the dawn and dusk hours (ex: white-tailed deer, some bats)
While
circadian rhythms
A circadian rhythm (), or circadian cycle, is a natural, internal process that regulates the sleep–wake cycle and repeats roughly every 24 hours. It can refer to any process that originates within an organism (i.e., endogenous) and responds to ...
are defined as regulated by
endogenous processes, other biological cycles may be regulated by exogenous signals. In some cases, multi-trophic systems may exhibit rhythms driven by the circadian clock of one of the members (which may also be influenced or reset by external factors). The endogenous plant cycles may regulate the activity of the bacterium by controlling availability of plant-produced photosynthate.
Many other important cycles are also studied, including:
*
Infradian rhythm
In chronobiology, an infradian rhythm is a rhythm with a period longer than the period of a circadian rhythm, i.e., with a frequency of less than one cycle in 24 hours. Some examples of infradian rhythms in mammals include menstruation, breeding, m ...
s, which are cycles longer than a day. Examples include
circannual or annual cycles that govern migration or reproduction cycles in many plants and animals, or the human
menstrual cycle.
*
Ultradian rhythm
In chronobiology, an ultradian rhythm is a recurrent period or cycle repeated throughout a 24-hour day. In contrast, circadian rhythms complete one cycle daily, while infradian rhythms such as the human menstrual cycle have periods longer than ...
s, which are cycles shorter than 24 hours, such as the 90-minute
REM cycle
Rapid eye movement sleep (REM sleep or REMS) is a unique phase of sleep in mammals and birds, characterized by random rapid movement of the eyes, accompanied by low muscle tone throughout the body, and the propensity of the sleeper to dream viv ...
, the 4-hour
nasal cycle
The nasal cycle is the unconscious alternating partial congestion and decongestion of the nasal cavities in humans and other animals. This results in greater airflow through one nostril with periodic alternation between the nostrils. It is a ph ...
, or the 3-hour cycle of
growth hormone
Growth hormone (GH) or somatotropin, also known as human growth hormone (hGH or HGH) in its human form, is a peptide hormone that stimulates growth, cell reproduction, and cell regeneration in humans and other animals. It is thus important in h ...
production.
*
Tidal rhythms, commonly observed in marine life, which follow the roughly 12.4-hour transition from high to low tide and back.
*
Lunar rhythms, which follow the
lunar month
In lunar calendars, a lunar month is the time between two successive syzygies of the same type: new moons or full moons. The precise definition varies, especially for the beginning of the month.
Variations
In Shona, Middle Eastern, and Eur ...
(29.5 days). They are relevant e.g. for marine life, as the level of the tides is modulated across the lunar cycle.
*
Gene oscillations – some genes are
expressed more during certain hours of the day than during other hours.
Within each cycle, the time period during which the process is more active is called the ''
acrophase''. When the process is less active, the cycle is in its ''
bathyphase'' or ''trough'' phase. The particular moment of highest activity is the ''peak'' or ''maximum''; the lowest point is the ''nadir''.
History
A circadian cycle was first observed in the 18th century in the movement of plant leaves by the French scientist
Jean-Jacques d'Ortous de Mairan. In 1751 Swedish
botanist
Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this field. The term "botany" comes from the Ancient Greek wo ...
and
naturalist Carl Linnaeus
Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his ennoblement in 1761 as Carl von Linné Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalised binomial nomenclature, the ...
(Carl von Linné) designed a
flower clock using certain species of
flowering plant
Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek words ('container, vessel') and ('seed'), and refers to those plants th ...
s. By arranging the selected species in a circular pattern, he designed a clock that indicated the time of day by the flowers that were open at each given hour. For example, among members of the
daisy family, he used the
hawk's beard plant which opened its flowers at 6:30 am and the
hawkbit
''Leontodon'' is a genus of plants in the tribe Cichorieae within the family Asteraceae, commonly known as hawkbits.
Their English name derives from the mediaeval belief that hawks ate the plant to improve their eyesight. Although originally on ...
which did not open its flowers until 7 am.
The 1960 symposium at
Cold Spring Harbor Laboratory
Cold Spring Harbor Laboratory (CSHL) is a private, non-profit institution with research programs focusing on cancer, neuroscience, plant biology, genomics, and quantitative biology.
It is one of 68 institutions supported by the Cancer Centers ...
laid the groundwork for the field of chronobiology.
It was also in 1960 that
Patricia DeCoursey invented the
phase response curve
A phase response curve (PRC) illustrates the transient change ( phase response) in the cycle period of an oscillation induced by a perturbation as a function of the phase at which it is received. PRCs are used in various fields; examples of biol ...
, one of the major tools used in the field since.
Franz Halberg of the
University of Minnesota
The University of Minnesota, formally the University of Minnesota, Twin Cities, (UMN Twin Cities, the U of M, or Minnesota) is a public university, public Land-grant university, land-grant research university in the Minneapolis–Saint Paul, Tw ...
, who coined the word ''circadian'', is widely considered the "father of American chronobiology." However, it was
Colin Pittendrigh and not Halberg who was elected to lead the ''Society for Research in Biological Rhythms'' in the 1970s. Halberg wanted more emphasis on the human and medical issues while Pittendrigh had his background more in evolution and ecology. With Pittendrigh as leader, the Society members did basic research on all types of organisms, plants as well as animals. More recently it has been difficult to get funding for such research on any other organisms than mice, rats, humans and
fruit flies
Fruit fly may refer to:
Organisms
* Drosophilidae, a family of small flies, including:
** ''Drosophila'', the genus of small fruit flies and vinegar flies
** ''Drosophila melanogaster'' or common fruit fly
** '' Drosophila suzukii'' or Asian frui ...
.
The role of Retinal Ganglion cells
Melanopsin as a circadian photopigment
In 2002,
Hattar and his colleagues showed that
melanopsin plays a key role in a variety of photic responses, including
pupillary light reflex
The pupillary light reflex (PLR) or photopupillary reflex is a reflex that controls the diameter of the pupil, in response to the intensity (luminance) of light that falls on the retinal ganglion cells of the retina in the back of the eye, ther ...
, and synchronization of the
biological clock to daily light-dark cycles. He also described the role of melanopsin in
ipRGCs
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 ...
. Using a rat melanopsin gene, a melanopsin-specific antibody, and
fluorescent immunocytochemistry, the team concluded that melanopsin is expressed in some RGCs. Using a
Beta-galactosidase
β-Galactosidase (EC 3.2.1.23, lactase, beta-gal or β-gal; systematic name β-D-galactoside galactohydrolase), is a glycoside hydrolase enzyme that catalyzes hydrolysis of terminal non-reducing β-D-galactose residues in β-D-galactosides.
β- ...
assay, they found that these RGC
axons exit the eyes together with the
optic nerve
In neuroanatomy, the optic nerve, also known as the second cranial nerve, cranial nerve II, or simply CN II, is a paired cranial nerve that transmits visual information from the retina to the brain. In humans, the optic nerve is derived fro ...
and project to the
suprachiasmatic nucleus (SCN), the primary circadian pacemaker in
mammal
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...
s. They also demonstrated that the RGCs containing melanopsin were intrinsically photosensitive. Hattar concluded that melanopsin is the photopigment in a small subset of RGCs that contributes to the intrinsic photosensitivity of these cells and is involved in their non-image forming functions, such as photic entrainment and pupillary light reflex.
Melanopsin cells relay inputs from rods and cones
![Phototransduction and ipRGCs in mammals](https://upload.wikimedia.org/wikipedia/commons/3/39/Phototransduction_and_ipRGCs_in_mammals.jpg)
Hattar, armed with the knowledge that melanopsin was the photopigment responsible for the photosensitivity of ipRGCs, set out to study the exact role of the ipRGC in photoentrainment. In 2008, Hattar and his research team transplanted
diphtheria
Diphtheria is an infection caused by the bacterium '' Corynebacterium diphtheriae''. Most infections are asymptomatic or have a mild clinical course, but in some outbreaks more than 10% of those diagnosed with the disease may die. Signs and s ...
toxin
genes
In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...
into the
mouse
A mouse ( : mice) is a small rodent. Characteristically, mice are known to have a pointed snout, small rounded ears, a body-length scaly tail, and a high breeding rate. The best known mouse species is the common house mouse (''Mus musculus' ...
melanopsin gene locus to create
mutant
In biology, and especially in genetics, a mutant is an organism or a new genetic character arising or resulting from an instance of mutation, which is generally an alteration of the DNA sequence of the genome or chromosome of an organism. It ...
mice that lacked ipRGCs. The research team found that while the mutants had little difficulty identifying visual targets, they could not entrain to light-dark cycles. These results led Hattar and his team to conclude that ipRGCs do not affect image-forming vision, but significantly affect non-image forming functions such as photoentrainment.
Distinct ipRGCs
Further research has shown that ipRGCs project to different brain nuclei to control both non-image forming and image forming functions.
These brain regions include the SCN, where input from ipRGCs is necessary to photoentrain circadian rhythms, and the
olivary pretectal nucleus
In neuroanatomy, the pretectal area, or pretectum, is a midbrain structure composed of seven nuclei and comprises part of the subcortical visual system. Through reciprocal bilateral projections from the retina, it is involved primarily in mediati ...
(OPN), where input from ipRGCs control the pupillary light reflex.
Hattar and colleagues conducted research that demonstrated that ipRGCs project to hypothalamic, thalamic, stratal, brainstem and limbic structures. Although ipRGCs were initially viewed as a uniform population, further research revealed that there are several subtypes with distinct morphology and physiology.
Since 2011, Hattar's laboratory has contributed to these findings and has successfully distinguished subtypes of ipRGCs.
Diversity of ipRGCs
Hattar and colleges utilized
Cre-based strategies for labeling ipRGCs to reveal that there are at least five ipRGC subtypes that project to a number of central targets.
Five classes of ipRGCs, M1 through M5, have been characterized to date in rodents. These classes differ in morphology, dendritic localization, melanopsin content, electrophysiological profiles, and projections.
Diversity in M1 cells
Hattar and his co-workers discovered that, even among the subtypes of ipRGC, there can be designated sets that differentially control circadian versus pupillary behavior. In experiments with M1 ipRGCs, they discovered that the transcription factor
Brn3b is expressed by M1 ipRGCs that target the OPN, but not by ones that target the SCN. Using this knowledge, they designed an experiment to cross Melanopsin-
Cre mice with mice that conditionally expressed a toxin from the Brn3b locus. This allowed them to selectively ablate only the OPN projecting M1 ipRGCS, resulting in a loss of pupil reflexes. However, this did not impair circadian photo entrainment. This demonstrated that the M1 ipRGC consist of molecularly distinct subpopulations that innervate different brain regions and execute specific light-induced functions.
This isolation of a 'labeled line' consisting of differing molecular and functional properties in a highly specific ipRGC subtype was an important first for the field. It also underscored the extent to which molecular signatures can be used to distinguish between RGC populations that would otherwise appear the same, which in turn facilitates further investigation into their specific contributions to visual processing.
Psychological impact of light exposure
Previous studies in circadian biology have established that exposure to light during abnormal hours leads to
sleep deprivation and disruption of the circadian system, which affect mood and
cognitive functioning. While this indirect relationship had been corroborated, not much work had been done to examine whether there was a direct relationship between irregular light exposure, aberrant mood, cognitive function, normal sleep patterns and circadian oscillations. In a study published in 2012, the Hattar Laboratory was able to show that deviant light cycles directly induce
depression-like symptoms and lead to impaired learning in mice, independent of
sleep
Sleep is a sedentary state of mind and body. It is characterized by altered consciousness, relatively inhibited sensory activity, reduced muscle activity and reduced interactions with surroundings. It is distinguished from wakefulness by a de ...
and circadian oscillations.
Effect on mood
ipRGCs project to areas of the brain that are important for regulating circadian rhythmicity and sleep, most notably the
SCN, subparaventricular nucleus, and the ventrolateral preoptic area. In addition, ipRGCs transmit information to many areas in the
limbic system, which is strongly tied to emotion and memory. To examine the relationship between deviant light exposure and behavior, Hattar and his colleagues studied mice exposed to alternating 3.5-hour light and dark periods (T7 mice) and compared them with mice exposed to alternating 12-hour light and dark periods (T24 mice). Compared to a T24 cycle, the T7 mice got the same amount of total sleep and their circadian expression of
PER2
PER2 is a protein in mammals encoded by the ''PER2'' gene. ''PER2'' is noted for its major role in circadian rhythms.
Discovery
The ''per ''gene'' ''was first discovered using forward genetics in '' Drosophilla melanogaster'' in 1971. Mammalia ...
, an element of the SCN pacemaker, was not disrupted. Through the T7 cycle, the mice were exposed to light at all circadian phases. Light pulses presented at night lead to expression of the transcription factor
c-Fos in the
amygdala
The amygdala (; plural: amygdalae or amygdalas; also '; Latin from Greek, , ', 'almond', 'tonsil') is one of two almond-shaped clusters of nuclei located deep and medially within the temporal lobes of the brain's cerebrum in complex verte ...
,
lateral habenula, and subparaventricular nucleus further implicating light's possible influence on mood and other cognitive functions.
Mice subjected to the T7 cycle exhibited depression-like symptoms, exhibiting decreased preference for
sucrose (sucrose anhedonia) and exhibiting more immobility than their T24 counterparts in the
forced swim test (FST). Additionally, T7 mice maintained rhythmicity in serum
corticosterone
Corticosterone, also known as 17-deoxycortisol and 11β,21-dihydroxyprogesterone, is a 21-carbon steroid hormone of the corticosteroid type produced in the cortex of the adrenal glands. It is of minor importance in humans, except in the very rar ...
, however the levels were elevated compared to the T24 mice, a trend that is associated with depression. Chronic administration of the antidepressant
Fluoxetine lowered corticosterone levels in T7 mice and reduced depression-like behavior while leaving their circadian rhythms unaffected.
Effect on learning
The
hippocampus
The hippocampus (via Latin from Greek , 'seahorse') is a major component of the brain of humans and other vertebrates. Humans and other mammals have two hippocampi, one in each side of the brain. The hippocampus is part of the limbic system, a ...
is a structure in the limbic system that receives projections from ipRGCs. It is required for the consolidation of
short-term memories into
long-term memories as well as spatial orientation and navigation. Depression and heightened serum corticosterone levels are linked to impaired hippocampal learning. Hattar and his team analyzed the T7 mice in the
Morris water maze (MWM), a spatial learning task that places a mouse in a small pool of water and tests the mouse's ability to locate and remember the location of a rescue platform located just below the waterline. Compared to the T24 mice, the T7 mice took longer to find the platform in subsequent trials and did not exhibit a preference for the quadrant containing the platform. In addition, T7 mice exhibited impaired hippocampal
long-term potentiation
In neuroscience, long-term potentiation (LTP) is a persistent strengthening of synapses based on recent patterns of activity. These are patterns of synaptic activity that produce a long-lasting increase in signal transmission between two neurons ...
(LTP) when subjected to
theta burst stimulation (TBS). Recognition memory was also affected, with T7 mice failing to show preference for novel objects in the novel object recognition test.
Necessity of ipRGCs
Mice without (Opn4
aDTA/aDTA mice) are not susceptible to the negative effects of an aberrant light cycle, indicating that light information transmitted through these cells plays an important role in regulation of mood and cognitive functions such as learning and memory.
Research developments
;Light and melatonin
More recently,
light therapy
Light therapy, also called phototherapy or bright light therapy is intentional daily exposure to direct sunlight or similar-intensity artificial light in order to treat medical disorders, especially seasonal affective disorder (SAD) and circad ...
and
melatonin administration have been explored by
Alfred J. Lewy (
OHSU
Oregon Health & Science University (OHSU) is a
public research university focusing primarily on health sciences with a main campus, including two hospitals, in Portland, Oregon. The institution was founded in 1887 as the University of Oregon Med ...
),
Josephine Arendt
Josephine may refer to:
People
* Josephine (given name), a given name (including a list of people with the name)
* Josephine (singer), a Greek pop singer
Places
*Josephine, Texas, United States
*Mount Josephine (disambiguation)
* Josephine Coun ...
(
University of Surrey, UK) and other researchers as a means to reset animal and human circadian rhythms. Additionally, the presence of low-level light at night accelerates circadian re-entrainment of hamsters of all ages by 50%; this is thought to be related to simulation of moonlight.
In the second half of 20th century, substantial contributions and formalizations have been made by Europeans such as
Jürgen Aschoff
Jürgen Walther Ludwig Aschoff (January 25, 1913 – October 12, 1998) was a German physician, biologist and behavioral physiologist. Together with Erwin Bünning and Colin Pittendrigh, he is considered to be a co-founder of the field of chrono ...
and
Colin Pittendrigh, who pursued different but complementary views on the phenomenon of
entrainment
Entrainment may refer to:
* Air entrainment, the intentional creation of tiny air bubbles in concrete
* Brainwave entrainment, the practice of entraining one's brainwaves to a desired frequency
* Entrainment (biomusicology), the synchronization o ...
of the circadian system by light (parametric, continuous, tonic, gradual vs. nonparametric, discrete, phasic, instantaneous, respectively).
;Chronotypes
Humans can have a propensity to be morning people or evening people; these behavioral preferences are called
chronotype
A chronotype is the behavioral manifestation of underlying circadian rhythm's myriad of physical processes. A person's chronotype is the propensity for the individual to sleep at a particular time during a 24-hour period. ''Eveningness'' (delayed ...
s for which there are various assessment questionnaires and biological marker correlations.
;Mealtimes
There is also a food-entrainable biological clock, which is not confined to the suprachiasmatic nucleus. The location of this clock has been disputed. Working with mice, however, Fuller ''et al.'' concluded that the food-entrainable clock seems to be located in the dorsomedial
hypothalamus
The hypothalamus () is a part of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrine system via the pituitary gland. The hypothalamu ...
. During restricted feeding, it takes over control of such functions as activity timing, increasing the chances of the animal successfully locating food resources.
;Diurnal patterns on the Internet
In 2018 a study published in PLoS ONE showed how 73 psychometric indicators measured on Twitter Content follow a diurnal pattern.
A followup study appeared on Chronobiology International in 2021 showed that these patterns were not disrupted by the 2020 UK lockdown.
;Modulators of circadian rhythms
In 2021, scientists reported the development of a light-responsive days-lasting modulator of circadian rhythms of tissues
via Ck1 inhibition. Such modulators may be useful for chronobiology research and repair of organs that are "out of sync".
Other fields
Chronobiology is an interdisciplinary field of investigation. It interacts with medical and other research fields such as
sleep medicine
Sleep medicine is a medical specialty or subspecialty devoted to the diagnosis and therapy of sleep disturbances and disorders. From the middle of the 20th century, research has provided increasing knowledge and answered many questions about ...
,
endocrinology
Endocrinology (from '' endocrine'' + '' -ology'') is a branch of biology and medicine dealing with the endocrine system, its diseases, and its specific secretions known as hormones. It is also concerned with the integration of developmental event ...
,
geriatrics
Geriatrics, or geriatric medicine, is a medical specialty focused on providing care for the unique health needs of older adults. The term ''geriatrics'' originates from the Greek γέρων ''geron'' meaning "old man", and ιατρός ''iatros ...
,
sports medicine
Sports medicine is a branch of medicine that deals with physical fitness and the treatment and prevention of injuries related to sports and exercise. Although most sports teams have employed team physicians for many years, it is only since the ...
,
space medicine
Space medicine is the practice of medicine on astronauts in outer space whereas astronautical hygiene is the application of science and technology to the prevention or control of exposure to the hazards that may cause astronaut ill health. Both ...
and
photoperiodism
Photoperiodism is the physiological reaction of organisms to the length of night or a dark period. It occurs in plants and animals. Plant photoperiodism can also be defined as the developmental responses of plants to the relative lengths of light a ...
.
See also
*
Bacterial circadian rhythms Bacterial circadian rhythms, like other circadian rhythms, are endogenous "biological clocks" that have the following three characteristics: (a) in constant conditions (i.e. constant temperature and either constant light or constant darkness ) they ...
*
Biological clock (aging)
An epigenetic clock is a biochemical test that can be used to measure age. The test is based on DNA methylation levels, measuring the accumulation of methyl groups to one's DNA molecules.
History
The strong effects of age on DNA methylation leve ...
*
Circadian rhythm
*
Circannual cycle
A circannual cycle is a biological process that occurs in living creatures over the period of approximately one year. This cycle was first discovered by Ebo Gwinner and Canadian biologist Ted Pengelley. It is classified as an Infradian rhythm, whi ...
*
Circaseptan
A circaseptan rhythm is a cycle consisting of approximately 7 days in which many biological processes of life, such as cellular immune system activity, resolve.
See also
*Circadian rhythm
*Chronobiology
Chronobiology is a field of biology th ...
, 7-day biological cycle
*
Familial sleep traits
*
Frank A. Brown, Jr.
*
Hitoshi Okamura
Hitoshi Okamura (born December 2, 1952) is a Japanese scientist who specializes in chronobiology. He is currently a Professor of Systems Biology at Kyoto University Graduate School of Pharmaceutical Sciences and the Research Director of the Japan ...
*
Light effects on circadian rhythm
Light effects on circadian rhythm are the effects that light has on circadian rhythm.
Most animals and other organisms have "built-in clocks" in their brains that regulate the timing of biological processes and daily behavior. These "clocks" are ...
*
Photoperiodism
Photoperiodism is the physiological reaction of organisms to the length of night or a dark period. It occurs in plants and animals. Plant photoperiodism can also be defined as the developmental responses of plants to the relative lengths of light a ...
*
Suprachiasmatic nucleus
*
Scotobiology
Scotobiology is the study of biology as directly and specifically affected by darkness, as opposed to photobiology, which describes the biological effects of light.
Overview
The science of scotobiology gathers together under a single descriptive ...
*
Time perception
The study of time perception or chronoception is a field within psychology, cognitive linguistics and neuroscience that refers to the subjective experience, or sense, of time, which is measured by someone's own perception of the duration of the ind ...
References
Further reading
* Hastings, Michael, "
The brain, circadian rhythms, and clock genes'". Clinical review" ''BMJ'' 1998;317:1704-1707 19 December.
* U.S. Congress, Office of Technology Assessment, "
Biological Rhythms: Implications for the Worker'". U.S. Government Printing Office, September 1991. Washington, DC. OTA-BA-463. NTIS PB92-117589
* Ashikari, M., Higuchi, S., Ishikawa, F., and Tsunetsugu, Y., "
'". Sunday, 25 August 2002
*"''Biorhythm experiment management plan''", NASA, Ames Research Center. Moffett Field, 1983.
* "''Biological Rhythms and Human Adaptation to the Environment''". US Army Medical Research and Materiel Command (AMRMC), US Army Research Institute of Environmental Medicine.
* Ebert, D., K.P. Ebmeier, T. Rechlin, and W.P. Kaschka, "''Biological Rhythms and Behavior''", ''Advances in Biological Psychiatry''. ISSN 0378-7354
* Horne, J.A. (Jim) & Östberg, Olov (1976). A Self-Assessment Questionnaire to determine Morningness-Eveningness in Human Circadian Rhythms. International Journal of Chronobiology, 4, 97–110.
* Roenneberg, Till, Cologne (2010). Wie wir ticken – Die Bedeutung der Chronobiologie für unser Leben, Dumont, .
The Linnean Society of London
External links
Halberg Chronobiology Centerat the
University of Minnesota
The University of Minnesota, formally the University of Minnesota, Twin Cities, (UMN Twin Cities, the U of M, or Minnesota) is a public university, public Land-grant university, land-grant research university in the Minneapolis–Saint Paul, Tw ...
, founded by
Franz Halberg, the "Father of Chronobiology"
*The
University of Virginia
The University of Virginia (UVA) is a Public university#United States, public research university in Charlottesville, Virginia. Founded in 1819 by Thomas Jefferson, the university is ranked among the top academic institutions in the United S ...
offers a
online tutorialon chronobiology.
*See the
Science Museum of Virginia
The Science Museum of Virginia is a science museum located in Richmond, Virginia. Established in 1970, it is an agency of the Commonwealth of Virginia. It is housed in the former Broad Street Station, built in 1917.
History
Early proposals
In 1 ...
publicatio
Can plants tell time?*Th
University of Manchesterhas an informativ
S Ertel's analysis of Chizhevsky's work
{{Neuroscience
Biological processes
Circadian rhythm
Neuroscience