Search a Darker Sky: A Cleft Mind
After all, there are many more astrocytes in the brain than there are neurons. Perhaps, some scientists have speculated, astrocytes carry out their own computing. Instead of the digital code of voltage spikes that neurons use, astrocytes may act more like an analog network, encoding information in slowly rising and falling waves of calcium. Until recently, studies of astrocytes examined only a few cells sitting in a petri dish. Axel Nimmerjahn of Stanford University and his colleagues, for instance, developed a way to mount microscopes on the skulls of mice. To watch the astrocytes, they inject molecules into the mice that glow when they bind to free calcium.
Whenever a mouse moves one of its legs, Nimmerjahn and his colleagues can see a little burst of calcium waves. In some cases, hundreds of astrocytes may flare up at once, and the flares can last as long as several seconds. Astrocytes are also vital for synapses. Stanford University neuroscientist Ben Barres and his colleagues found that neurons that grew with astrocytes formed nearly 10 times as many synapses as neurons growing without them, and the activity in those synapses was nearly times greater.
Since synapses change as we learn and form new memories, Marie E. Gibbs of Monash University in Australia suspected that astrocytes might be important to our ability to learn. To test that idea, she and her colleagues gave chicks colored beads to peck at. The red beads were coated in a bitter chemical; usually a single peck was enough to make the chicks learn never to peck a red bead again. But when they were injected with a drug that prevented astrocytes from synthesizing glutamate, the birds were unable to remember the bad taste and would peck at the beads again.
But these sorts of experiments have not swayed some skeptics. Ken McCarthy, a neuroscientist at the University of North Carolina at Chapel Hill, and his colleagues engineered mice to grow astrocytes that lack a key protein required to pry open their calcium packets. These mice grew up to be indistinguishable from ordinary ones, for reasons still unclear. There is something marvelous in the fact that we barely understand what most of the cells in our brains are doing. Beginning in the s, astronomers realized that all the things they could see through their telescopes—the stars, the galaxies, the nebulas—make up just a small fraction of the total mass of the universe.
The rest, known as dark matter, still defies their best attempts at explanation.
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Between our ears, it turns out, each of us carries a personal supply of dark matter as well. By Carl Zimmer Wednesday, August 19, You might also like. How Not to Choke Under Pressure. Bottles Full of Brain-Boosters. How I Became a Master of Memory. Could We Travel Through a Wormhole? Do Probiotics Really Work?
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Even healthy people who have no seasonal problems seem to experience this low-amplitude change over the year, with worse mood and energy during autumn and winter and an improvement in spring and summer, she says. Why should darker months trigger this tiredness and low mood in so many people? There are several theories, none of them definitive, but most relate to the circadian clock — the roughly hour oscillation in our behaviour and biology that influences when we feel hungry, sleepy or active. This is no surprise given that the symptoms of the winter blues seem to be associated with shortening days and longer nights, and that bright light seems to have an antidepressive effect.
Another is that some people produce more of a hormone called melatonin during winter than in summer — just like certain other mammals that show strong seasonal patterns in their behaviour. Levels of this hormone usually rise at night in response to darkness, helping us to feel sleepy, and are suppressed by the bright light of morning. Precisely why this should trigger feelings of depression is still unclear.
The Brain: The Dark Matter of the Human Brain | verfirerany.tk
One idea is that this tiredness could then have unhealthy knock-on effects. According to Daniel Kripke, an emeritus professor of psychiatry at the University of California, San Diego, when melatonin strikes a region of the brain called the hypothalamus, this alters the synthesis of another hormone — active thyroid hormone — that regulates all sorts of behaviours and bodily processes.
When dawn comes later in the winter, the end of melatonin secretion drifts later, says Kripke. From animal studies, it appears that high melatonin levels just after the time an animal wakes up strongly suppress the making of active thyroid hormone — and lowering thyroid levels in the brain can cause changes in mood, appetite and energy. For instance, thyroid hormone is known to influence serotonin, a neurotransmitter that regulates mood. Several studies have shown that levels of brain serotonin in humans are at their lowest in the winter and highest in the summer. In , scientists in Canada discovered that people with severe SAD show greater seasonal changes in a protein that terminates the action of serotonin than others with no or less severe symptoms, suggesting that the condition and the neurotransmitter are linked.
But regardless of what causes winter depression, bright light — particularly when delivered in the early morning — seems to reverse the symptoms. A month later, on 28 November , a newspaper story described Sam Eyde pushing the same idea, although it was another hundred years before it was realised. Instead, in Norsk Hydro erected a cable car as a gift to the townspeople, so that they could get high enough to soak up some sunlight in winter. Instead of bringing the sun to the people, the people would be brought to the sunshine. But after receiving a small grant from the local council to develop the idea, he learned about this history and started to develop some concrete plans.
These involved a heliostat: a mirror mounted in such a way that it turns to keep track of the sun while continually reflecting its light down towards a set target — in this case, Rjukan town square. The three mirrors, each measuring 17 m 2 , stand proud upon the mountainside above the town.
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In January, the sun is only high enough to bring light to the square for two hours per day, from midday until 2pm, but the beam produced by the mirrors is golden and welcoming. Stepping into the sunlight after hours in permanent shade, I become aware of just how much it shapes our perception of the world. When I leave the sunlight, Rjukan feels a flatter, greyer place. As far back as the sixth century, historians were describing seasonal peaks of joy and sorrow among Scandinavians, brought about by the continuous daylight of summer and its almost complete absence in winter.
In Sweden, an estimated 8 per cent of the population suffer from SAD, with a further 11 per cent said to suffer the winter blues. In early January, the sun rises at around 8. For Anna Odder Milstam, an English and Swedish teacher, this means getting up and arriving at work before dawn for several months of the year.
They are less alert and less active at this time of year.
Anna picks me up from my city-centre hotel at 7. Lindeborg School, where Anna teaches, caters for approximately pupils, ranging from preschool age through to Yet as my eyes adjust to the bright light, I see the curtains in this classroom are firmly closed. In front of me sit a class of year-olds at evenly spaced desks, watching my reaction with mild amusement. They then grow gradually more intense as the morning progresses, dimming slightly in the run up to lunch to ease the transition to the gloomier light outside.
Pete's children have grown up in the Himalayas, coming to Nepal every year since they were toddlers. The expedition members are among the first foreigners in modern times to visit Samdzong, which means "Earth fortress," named after a stronghold above the village, now a crumbling ruin. To show respect for local traditions, the expedition holds a "puja," a Buddhist offering to the mountain deities, before scouting cliff-side caves in the area. Pete's son, seven-year-old Finn, is the first to find a human bone, below some caves.
He shows it to bioarchaelogist, Jacqueline Eng. You can see it's a proximal humerus, on the right. Don't know what context this comes from, maybe washed down from somewhere. The cliffs have eroded over time, exposing the contents of the tombs, which were likely first accessed by shafts, dug by early people, from above.
PETE ATHANS: What we want to do is to quickly draw, label and then number, and then get them down to the scientists, so they can start to take a look at these things and give us an idea of what and whom they belong to. Because the caves are swiftly eroding, this vertical dig for artifacts and bones qualifies as rescue archaeology.
Although he has a fear of heights, Mark has to see the tombs himself, to fully understand the site. The part I hate the most is actually walking up that trail. It's really narrow, and you just make a dumb move, you're done. First, excess dirt from collapsed walls is removed from the caves. Then, the dirt is sifted to uncover the smallest artifacts.