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ThinkStock/Erin McCarthy
ThinkStock/Erin McCarthy

Do Animals Dream?

ThinkStock/Erin McCarthy
ThinkStock/Erin McCarthy

If you’ve ever seen a cat wiggling around in its sleep, or come across three different-sized beds after eating porridge in a bear family’s inexplicably furnished home, you’ve probably wondered if animals are capable of dreaming. Theirs might not involve Beyonce, your third grade classroom, and a radiator that turns into a snake for some reason like yours do, but some animals do have dreams. 

Most land mammals experience the Rapid Eye Movement (REM) sleep where dreams mainly occur, but since they don’t keep dream journals—at least not where we can find them—scientists tested rats to see what was going on in their brains when they slept. According to a 2001 report, MIT researchers Daniel Bedore and Matt Wilson placed trained rats on a track and monitored their brain activity while they moved towards their edible reward. They then monitored the rats’ brain activity while they were in a REM cycle. After examining the data, they saw that some activity in a sleeping rat’s brain matched some of its waking activity. The identical patterns led the scientists to believe that not only were the rats dreaming, they were dreaming about running on the track. 

Dr. Stanley Coren, a psychology professor and neuropsychological researcher, writes in his book How Dogs Think: Understanding the Canine Mind, that dogs also dream. Like rats, pooches dream about common scenes they have experienced in their waking lives. Dr. Coren also notes that the smaller a dog is, the more it will dream:

A small dog, such as a toy poodle, may dream once every ten minutes, while a dog as large as a mastiff or an Irish wolfhound may spend an hour and a half between each dream.

Mammals aren’t the only critters that dream, though. Neuroscientists Amish S. Dave and Daniel Margoliash of the University of Chicago have found that the sleeping brain activity of older male zebra finches can fall into patterns that are identical to those observed when the birds are singing. And since the male zebra finch uses its songs to attract a mate, they win our completely made up award for most interesting animal dreams.

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Big Questions
How Do Hummingbirds Sleep?
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How do hummingbirds sleep?

Anusha Shankar:

Ooh this is an exciting question—I’ve spent the past five years thinking about just this!

Look at these infrared images from a crowdfunded project we did in the summer of 2017: The bird on the left is generating heat, keeping itself warm, while the one on the right is in torpor. It has allowed its body temperature to become the same as the air temperature and has stopped "thermoregulating," or maintaining a high body temperature.

Hummingbirds find a nice and sheltered place at night, and they latch onto a branch with their tiny feet, and then they go to sleep. Some of them ... use a strategy called torpor, where they can lower the amount of energy they use by about 85 percent. They do this by basically shutting down a bunch of their bodily functions—they allow their body to get cold as the night gets colder. You and I spend a lot of energy keeping our bodies warm so everything functions normally. Hummingbirds in torpor give up this "normal" function, and become more like lizards, in that they can get ‘cold-blooded’ in torpor.

Torpor is a tricky state to be in, because they can’t respond to outside stimuli for 20 to 30 minutes, until they warm their bodies back up. They take that risk just to have enough energy in their tiny bodies to make it to the next morning.

I recently wrote a blog post for National Geographic to talk a bit more about hummingbird sleep (includes videos!).

This post originally appeared on Quora. Click here to view.

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Big Questions
Are There Number 1 Pencils?
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Almost every syllabus, teacher, and standardized test points to the ubiquitous No. 2 pencil, but are there other choices out there?

Of course! Pencil makers manufacture No. 1, 2, 2.5, 3, and 4 pencils—and sometimes other intermediate numbers. The higher the number, the harder the core and lighter the markings. (No. 1 pencils produce darker markings, which are sometimes preferred by people working in publishing.)

The current style of production is profiled after pencils developed in 1794 by Nicolas-Jacques Conté. Before Conté, pencil hardness varied from location to location and maker to maker. The earliest pencils were made by filling a wood shaft with raw graphite, leading to the need for a trade-wide recognized method of production.

Conté’s method involved mixing powdered graphite with finely ground clay; that mixture was shaped into a long cylinder and then baked in an oven. The proportion of clay versus graphite added to a mixture determines the hardness of the lead. Although the method may be agreed upon, the way various companies categorize and label pencils isn't.

Today, many U.S.  companies use a numbering system for general-purpose, writing pencils that specifies how hard the lead is. For graphic and artist pencils and for companies outside the U.S., systems get a little complicated, using a combination of numbers and letters known as the HB Graphite Scale.

"H" indicates hardness and "B" indicates blackness. Lowest on the scale is 9H, indicating a pencil with extremely hard lead that produces a light mark. On the opposite end of the scale, 9B represents a pencil with extremely soft lead that produces a dark mark. ("F" also indicates a pencil that sharpens to a fine point.) The middle of the scale shows the letters and numbers that correspond to everyday writing utensils: B = No. 1 pencils, HB = No. 2, F = No. 2½, H = No. 3, and 2H = No. 4 (although exact conversions depend on the brand).

So why are testing centers such sticklers about using only No. 2 pencils? They cooperate better with technology because early machines used the electrical conductivity of the lead to read the pencil marks. Early scanning-and-scoring machines couldn't detect marks made by harder pencils, so No. 3 and No. 4 pencils usually resulted in erroneous results. Softer pencils like No. 1s smudge, so they're just impractical to use. So No. 2 pencils became the industry standard.

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