.
According
to a new study, a biological clock circuit may explain why people with
Alzheimer's disease or other forms of dementia can become more agitated or
aggressive in the early evening. "Sundowning"
is common in people with Alzheimer's where they feel more agitated during the
evening.
A report published in the journal Nature Neuroscience, explains, for the first time, how the biological clock links to brain cells, or neurons, that control aggression.
"The biological clock's brain circuitry has a connection to a population of neurons known to cause violent attacks when stimulated."
It usually begins or gets worse in the late afternoon or early evening — as the sun goes down and daylight starts to fade. This is often the time when caregivers are tired and need to take a break.
Possible causes of Sundowning.
Another potential cause : Brain changes wrought by neurodegenerative diseases such as Alzheimer's interfere with the biological clock. It is not known whether or not the clock "directly regulates aggressive behavior."
Most living things, from microbes to plants and animals, have circadian rhythms. For example, being awake during the day and asleep at night is a circadian rhythm that arises from biological clocks responding to changes in light levels in the organism's environment.
While biological clocks are found nearly everywhere in the body, they are
all synchronized by a "master clock" in the brain.
In humans, mice, and other vertebrates, the master clock is located in the Supra-Chiasmatic nucleus, which is a cluster of neurons inside the hypothalamus region of the brain. The cluster contains around 20,000 cells and receives signals directly from the eyes.
"One is more likely to be aggressive in the early evening around lights out, and least aggressive in the early morning, around lights on."
"It looks like aggressiveness builds up in mice during the lights on period, and reaches a peak around the end of the light period."
Manipulation of master biological clock by tweaking genes in the neurons that regulate it show that when they stopped the master clock neurons from being able to make a specific chemical messenger, or neurotransmitter, the one loses one’s circadian pattern of aggression. Aggressiveness remained high all the time, showing no highs and lows.
A tool called optogenetics was used to map the brain circuits involved. The tool uses laser light to stimulate and deactivate targeted brain cells.
Hence there seems to be a "functional" circuit through which "the suprachiasmatic nucleus [Master] clock regulates aggression."
The patterns observed in the study mimic the patterns of increased aggression seen in patients during Sundowning."
The circuit is damaged in some way in neurodegenerative diseases such as Alzheimer's.
Further research into how this biological clock circuit changes in people with Alzheimer's disease could be very useful in helping to improve quality of life for patients and caregivers.
"Sundowning is often the reason that patients have to be institutionalized, and if clinicians can control this circuit to minimize aggressiveness at the end of the day, patients may be able to live at home longer."
Most of these researches were done in mice. Scientists have discovered that the genes that make and control the various components of biological clocks are largely similar in humans, mice, fruit flies, fungi, and many other organisms.
Sun-downing in Alzheimer's: Clue to the cause of evening agitation
Sun-downing in Alzheimer's: Clue to the cause of evening agitation
A report published in the journal Nature Neuroscience, explains, for the first time, how the biological clock links to brain cells, or neurons, that control aggression.
"The biological clock's brain circuitry has a connection to a population of neurons known to cause violent attacks when stimulated."
What is sundowning?
Sundowning is a condition that is typically seen in people with Alzheimer's disease, when behavior becomes restless, agitated, and aggressive, accompanied by confusion.It usually begins or gets worse in the late afternoon or early evening — as the sun goes down and daylight starts to fade. This is often the time when caregivers are tired and need to take a break.
Possible causes of Sundowning.
1. Excessive
tiredness,
2. Pain,
or even
3. Depression,
4. Boredom,
5. Hunger,
6. Thirst.
Another potential cause : Brain changes wrought by neurodegenerative diseases such as Alzheimer's interfere with the biological clock. It is not known whether or not the clock "directly regulates aggressive behavior."
Biological clocks and circadian rhythm
Biological clocks are specific groups of proteins that communicate with cells in nearly every organ and most tissue in the body.
They respond to changes in light and dark in the environment and give rise to circadian rhythms — that is physical, behavioral, and mental changes that "follow a daily cycle."Most living things, from microbes to plants and animals, have circadian rhythms. For example, being awake during the day and asleep at night is a circadian rhythm that arises from biological clocks responding to changes in light levels in the organism's environment.
In humans, mice, and other vertebrates, the master clock is located in the Supra-Chiasmatic nucleus, which is a cluster of neurons inside the hypothalamus region of the brain. The cluster contains around 20,000 cells and receives signals directly from the eyes.
Circadian pattern of aggression
According to the study, the a circadian pattern of aggression — that is, their intensity and frequency depended on the time of day."One is more likely to be aggressive in the early evening around lights out, and least aggressive in the early morning, around lights on."
"It looks like aggressiveness builds up in mice during the lights on period, and reaches a peak around the end of the light period."
Manipulation of master biological clock by tweaking genes in the neurons that regulate it show that when they stopped the master clock neurons from being able to make a specific chemical messenger, or neurotransmitter, the one loses one’s circadian pattern of aggression. Aggressiveness remained high all the time, showing no highs and lows.
A tool called optogenetics was used to map the brain circuits involved. The tool uses laser light to stimulate and deactivate targeted brain cells.
Biological clock tied to aggression neurons
Two parallel circuits link the biological clock to a brain sub-region called the "ventrolateral part of the ventromedial hypothalamus," which is known to regulate aggression. Stimulating neurons here is known to cause one to become violent and aggressive.Hence there seems to be a "functional" circuit through which "the suprachiasmatic nucleus [Master] clock regulates aggression."
The patterns observed in the study mimic the patterns of increased aggression seen in patients during Sundowning."
The circuit is damaged in some way in neurodegenerative diseases such as Alzheimer's.
Further research into how this biological clock circuit changes in people with Alzheimer's disease could be very useful in helping to improve quality of life for patients and caregivers.
"Sundowning is often the reason that patients have to be institutionalized, and if clinicians can control this circuit to minimize aggressiveness at the end of the day, patients may be able to live at home longer."
Most of these researches were done in mice. Scientists have discovered that the genes that make and control the various components of biological clocks are largely similar in humans, mice, fruit flies, fungi, and many other organisms.
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