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How Your Brain Fights Sleep Even When You're Exhausted

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Maybe you’ve got an exam in the morning, or there’s just one more episode left in this season. Whatever the reason, tonight you ignore your body’s demands and stay up instead. It’s an impressive feat, if you think about it—sleep is essential—and now scientists may be closer to understanding how we do it. They published a report on their findings in the journal Neuron.

There’s a little section of your brainstem called the dorsal raphe nucleus (DRN). This region is responsible for making serotonin and other brain chemicals.

Lead researcher Viviana Gradinaru of Caltech says previous studies have also suggested that the dorsal raphe nucleus plays a role in helping keep us awake.

"People who have damage in this part of their brain have been shown to experience excessive daytime sleepiness,” she said in a statement, “but there was not a good understanding of the exact role of these neurons in the sleep/wake cycle and whether they react to internal or external stimuli to influence arousal."

Within the dorsal raphe nucleus lies a little-understood group of dopamine cells called the dorsal raphe nucleus neurons (DRNDA).

Color image of dorsal raphe nucleus neurons
Dorsal raphe nucleus neurons responding to light (green) and chemical (red) signals.
Viviana Gradinaru

Gradinaru and her colleagues wanted to know if voluntary wakefulness had anything to do with dopamine activity within these cells. They started by studying mouse brains, which are similar to our own in many ways.

The researchers monitored the rodents’ DRNDA action while the mice were fed, met new potential mates, or experienced sudden unpleasant sensations—all experiences for which the mice would want or need to stay awake. Throughout the experiences, the mice’s DRNDA cells kept very busy, sending bursts of dopamine to other parts of the brain.

Next, the scientists tracked DRNDA cell activity as the mice slept and woke. They found that the cells seemed to sleep when the mice did, and revved up when the mice got up.

So far, the researchers knew that the sleeping mouse/sleeping neurons and waking mouse/waking neurons pairs existed, but they couldn’t tell if the neurons caused the waking or vice versa.

To find out, they engineered DRNDA cells that could be switched on and off by light. They then bred mice with these light-sensitive cells and let them sleep. As the mice snoozed, the researchers switched on the lights and their DRNDA cells using a technique called optogenetics. Sure enough, the mice woke up.

Shutting off DRNDA cells had the opposite effect: Mice with no DRNDA activity couldn’t keep their eyes open, even when faced with danger, loud noises, or the possibility of mating.

The authors note that their experiments included only mice, and that it’s too soon to draw conclusions about what this might mean for people.

“Further work is necessary to establish causation in humans,” Gradinaru said, “and to test the potential of the DRNDA as a therapeutic target for insomnia or oversleeping, and for sleep disturbances that accompany other psychiatric disorders such as depression, bipolar disorder, and schizophrenia."

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Feeling Anxious? Just a Few Minutes of Meditation Might Help
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Some say mindfulness meditation can cure anything. It might make you more compassionate. It can fix your procrastination habit. It could ward off germs and improve health. And it may boost your mental health and reduce stress, anxiety, depression, and pain.

New research suggests that for people with anxiety, mindfulness meditation programs could be beneficial after just one session. According to Michigan Technological University physiologist John Durocher, who presented his work during the annual Experimental Biology meeting in San Diego, California on April 23, meditation may be able to reduce the toll anxiety takes on the heart in just one session.

As part of the study, Durocher and his colleagues asked 14 adults with mild to moderate anxiety to participate in an hour-long guided meditation session that encouraged them to focus on their breathing and awareness of their thoughts.

The week before the meditation session, the researchers had measured the participants' cardiovascular health (through data like heart rate and the blood pressure in the aorta). They evaluated those same markers immediately after the session ended, and again an hour later. They also asked the participants how anxious they felt afterward.

Other studies have looked at the benefits of mindfulness after extended periods, but this one suggests that the effects are immediate. The participants showed significant reduction in anxiety after the single session, an effect that lasted up to a week afterward. The session also reduced stress on their arteries. Mindfulness meditation "could help to reduce stress on organs like the brain and kidneys and help prevent conditions such as high blood pressure," Durocher said in a press statement, helping protect the heart against the negative effects of chronic anxiety.

But other researchers have had a more cautious outlook on mindfulness research in general, and especially on studies as small as this one. In a 2017 article in the journal Perspectives on Psychological Science, a group of 15 different experts warned that mindfulness studies aren't always trustworthy. "Misinformation and poor methodology associated with past studies of mindfulness may lead public consumers to be harmed, misled, and disappointed," they wrote.

But one of the reasons that mindfulness can be so easy to hype is that it is such a low-investment, low-risk treatment. Much like dentists still recommend flossing even though there are few studies demonstrating its effectiveness against gum disease, it’s easy to tell people to meditate. It might work, but if it doesn't, it probably won't hurt you. (It should be said that in rare cases, some people do report having very negative experiences with meditation.) Even if studies have yet to show that it can definitively cure whatever ails you, sitting down and clearing your head for a few minutes probably won't hurt.

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Scientists Use a CT Scanner to Give Whales a Hearing Test
Ted Cranford
Ted Cranford

It's hard to study how whales hear. You can't just give the largest animals in the world a standard hearing test. But it's important to know, because noise pollution is a huge problem underwater. Loud sounds generated by human activity like shipping and drilling now permeate the ocean, subjecting animals like whales and dolphins to an unnatural din that interferes with their ability to sense and communicate.

New research presented at the 2018 Experimental Biology meeting in San Diego, California suggests that the answer lies in a CT scanner designed to image rockets. Scientists in San Diego recently used a CT scanner to scan an entire minke whale, allowing them to model how it and other whales hear.

Many whales rely on their hearing more than any other sense. Whales use sonar to detect the environment around them. Sound travels fast underwater and can carry across long distances, and it allows whales to sense both predators and potential prey over the vast territories these animals inhabit. It’s key to communicating with other whales, too.

A CT scan of two halves of a dead whale
Ted Cranford, San Diego State University

Human technology, meanwhile, has made the ocean a noisy place. The propellers and engines of commercial ships create chronic, low-frequency noise that’s within the hearing range of many marine species, including baleen whales like the minke. The oil and gas industry is a major contributor, not only because of offshore drilling, but due to seismic testing for potential drilling sites, which involves blasting air at the ocean floor and measuring the (loud) sound that comes back. Military sonar operations can also have a profound impact; so much so that several years ago, environmental groups filed lawsuits against the U.S. Navy over its sonar testing off the coasts of California and Hawaii. (The environmentalists won, but the new rules may not be much better.)

Using the CT scans and computer modeling, San Diego State University biologist Ted Cranford predicted the ranges of audible sounds for the fin whale and the minke. To do so, he and his team scanned the body of an 11-foot-long minke whale calf (euthanized after being stranded on a Maryland beach in 2012 and preserved) with a CT scanner built to detect flaws in solid-fuel rocket engines. Cranford and his colleague Peter Krysl had previously used the same technique to scan the heads of a Cuvier’s beaked whale and a sperm whale to generate computer simulations of their auditory systems [PDF].

To save time scanning the minke calf, Cranford and the team ended up cutting the whale in half and scanning both parts. Then they digitally reconstructed it for the purposes of the model.

The scans, which assessed tissue density and elasticity, helped them visualize how sound waves vibrate through the skull and soft tissue of a whale’s head. According to models created with that data, minke whales’ hearing is sensitive to a larger range of sound frequencies than previously thought. The whales are sensitive to higher frequencies beyond those of each other’s vocalizations, leading the researchers to believe that they may be trying to hear the higher-frequency sounds of orcas, one of their main predators. (Toothed whales and dolphins communicate at higher frequencies than baleen whales do.)

Knowing the exact frequencies whales can hear is an important part of figuring out just how much human-created noise pollution affects them. By some estimates, according to Cranford, the low-frequency noise underwater created by human activity has doubled every 10 years for the past half-century. "Understanding how various marine vertebrates receive and process low-frequency sound is crucial for assessing the potential impacts" of that noise, he said in a press statement.

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