Why Don't Woodpeckers Get Brain Damage?

pablo_arriaran, istock/getty images plus
pablo_arriaran, istock/getty images plus

Hit your head really hard on something, and it’ll smart for a while. In worse cases, you might get a concussion, fracture your skull, or receive a brain injury that leaves you impaired or kills you (traumatic brain injuries account for nearly one third of injury-related deaths in the US).

Good thing you’re not a woodpecker, then. The lives and livelihoods of these birds revolve around slamming their heads into things. Whether it wants to get at an insect hiding in bark, excavate a space to build a nest, claim a bit of territory, or attract a mate, the woodpecker has one simple solution: bang its head against a tree trunk at speeds reaching 13 to 15 miles per hour. In an average day, a woodpecker does this around 12,000 times, and yet they don’t seem to hurt themselves or be the least bit bothered by it. This is because, after millions of years of this type of behavior, they’ve evolved some specialized headgear to prevent injuries to their heads, brains, and eyes.

To figure out what goes into woodpecker head trauma prevention, a team of Chinese scientists took a look at the birds’ skulls and brains and their pecking behavior. They watched as woodpeckers pecked at force sensors while recording them with high-speed cameras so they could see the strikes in slow motion and know how hard each blow was. They also scanned the birds’ heads with x-rays and an electron microscope to get a better look at their bone structure. Finally, they squished a few preserved woodpecker skulls in a material testing machine and, using their scans, built 3D computer models of the birds’ heads to smash in a simulation.

When all was said and done and both the virtual and actual woodpeckers' heads had taken a sound beating, the researchers found that there are a few anatomical features and other factors that come together to keep a woodpecker safe and healthy while it rat-a-tat-tats the day away.

First, a woodpecker’s skull is built to absorb shock and minimize damage. The bone that surrounds the brain is thick and spongy, and loaded with trabeculae, microscopic beam-like bits of bone that form a tightly woven “mesh” for support and protection. On their scans, the scientists found that this spongy bone is unevenly distributed in woodpeckers, and it is concentrated around the forehead and the back of the skull, where it could act as a shock absorber.

Woodpeckers' hyoid bones act as additional support structures. In humans, the horseshoe-shaped hyoid is an attachment site for certain throat and tongue muscles. Woodpeckers’ hyoids do the same job, but they’re much larger and are differently shaped. The ends of the “horseshoe” wrap all the way around the skull and, in some species, even around the eye socket or into the nasal cavity, eventually meeting to form a sort of sling shape. This bizarre-looking bone, the researchers think, acts like a safety harness for the woodpecker’s skull, absorbing shock stress and keeping it from shaking, rattling and rolling with each peck.

Inside the skull, the brain has its own defenses. It’s small and smooth, and is positioned in a tight space with its largest surface pointing towards the front of the skull. It doesn’t move around too much, and when it does collide with the skull, the force is spread out over a larger area. This makes it more resistant to concussions, the researchers say.

A woodpecker’s beak helps prevent trauma, too. The outer tissue layer of its upper beak is longer than the lower beak, creating a kind of overbite, and the bone structure of the lower beak is longer and stronger than the upper one. The researchers think that the uneven build diverts impact stress away from the brain and distributes it to the lower beak and bottom parts of the skull instead.

The woodpecker’s anatomy doesn’t just prevent injuries to the brain, but also its eyes. Other research using high-speed recordings has shown that, in the fraction of a second just before their beaks strike wood, woodpeckers’ thick nictitans—membranes beneath the lower lid of their eyes, sometimes called the “third eyelid”—close over the eyes. This protects them from debris and keeps them in place. They act like seatbelts, says ophthalmologist Ivan Schwab, author of Evolution's Witness: How Eyes Evolved, and they keep the retina from tearing and the eye from popping right out of the skull.

There’s also a behavioral aspect to the damage control. The researchers found that woodpeckers are pretty good at varying the paths of their pecks. By moving their heads and beaks around as they hammer away, they minimize the number of times in a row that the brain and skull make contact at the same point. Older research also showed that the strike trajectories, as much as they vary, are always almost linear. There’s very little, if any, rotation of the head and almost no movement immediately after impact, minimizing twisting force that could cause injury.

Earlier this year, another group of researchers in China found that, with all of these adaptations, 99.7 percent of the impact energy from striking a tree is absorbed by the body, but a little bit—that last 0.3 percent—does go to the head and the brain. That mechanical energy gets converted into heat, which causes the temperature of a woodpecker’s brain to increase, but the birds seem to have a way dealing with that, too. Woodpeckers usually peck in short bursts with breaks in between, and the researchers think that these pauses give the brain time to cool down before the head banging starts again and brings the temperature back up.

This story was originally published in 2012. It was updated with new information in 2014.

How Is a Sunscreen's SPF Calculated?

Rawpixel/iStock via Getty Images
Rawpixel/iStock via Getty Images

I’m a pale person. A very pale person. Which means that during these hot summer months, I carry sunscreen with me at all times, and apply it liberally. But I’ve never really understood what those SPF numbers meant, so I asked some sun care to break it down for me—and to tell me how to best apply the stuff so that I can make it through the summer without looking like a lobster.

Soaking up the sun ... safely

SPF stands for Sun Protection Factor, and it indicates a sunscreen’s ability to block UVB rays. The concept was pioneered at the Coppertone Solar Research Center in 1972; in 1978, the FDA published an SPF method based on Coppertone’s system, according to Dr. David Leffell, chief of Dermatologic Surgery and Cutaneous Oncology at Yale.

The numbers themselves stand for the approximate measure of time a person who has applied the sunscreen can stay out in the sun without getting burned. Say you get burned after 20 minutes in the sun without sunscreen; if properly applied (and reapplied), SPF 30 will allow you to stay in the sun 30 times longer without burning than if you were wearing no protection at all. So, theoretically, you should have approximately 600 minutes, or 10 hours, in the sun. But it’s not an exact science because the amount of UV light that reaches us depends on a number of factors, including cloud cover, the time of day, and the reflection of UV rays off the ground, so it’s generally recommended that you reapply sunscreen every two hours (or even sooner).

What gives a sunscreen a higher SPF comes down to the product’s formulation. “It’s possible that an SPF 50 might contain slightly more of one or more sunscreen active ingredients to achieve that higher SPF,” Dr. Patricia Agin, president of Agin Suncare Consulting, says. “But it’s also possible that the SPF 50 might contain an additional active ingredient to help boost the SPF performance to SPF 50.”

No matter what SPF your sunscreen is, you’ll still get a burn if it’s not properly applied. So let’s go over how to do that.

How to apply sunscreen

First, make sure you have a water-resistant, broad spectrum sunscreen—which means that it protects against both UVB and UVA radiation—with an SPF of at least 30. “Typically, you don’t have to buy sunscreen that has an SPF higher than that unless you have very sun sensitive skin,” Leffell says. “That’s a very small percentage of the population.” (Redheads, people with light eyes, and those who turn pink after just a few minutes in the sun—you’ll want to load up on SPF above 30.)

Twenty minutes before you go out to the beach or the pool, begin to apply your sunscreen in an even coat. “Don’t apply it like icing on a cake,” Leffell says. “I see these patients and they’ve got the tops of their ears covered with thick, unevenly applied sunscreen, and that’s not a good sign.” Sunscreen sprays will easily give you that even coat you need.

Whether you’re using lotion or a spray, when it comes time to apply, Leffell recommends starting with your scalp and face, even if you plan on wearing a hat. “Make sure you’ve covered the ears and nose and under the eyes,” Leffell says. “Then, I would move down to the shoulders, and make sure that someone can apply the sunscreen on your back beyond the reach of your hands.”

Other areas that are important that you may forget to cover, but shouldn’t, are the tops of your feet, the backs of your hands, and your chest. “We see it all the time now—the v of the chest in women has become a socially and aesthetically huge issue when they are 50 and beyond. Because even though they can treat their faces with all sorts of cosmetics and procedures, the chest is much harder, and they are stuck with the face of a 40-year-old and the chest of a 60-year-old. You want to avoid that using sunscreen.”

Another important thing to keep in mind: Water-resistant doesn’t mean waterproof. “I always tell patients to reapply every couple of hours while you’re active outdoors," Leffell says, "and always reapply when you come out of the water or if you’ve been sweating a lot, regardless of whether the label says water resistant."

Determining whether or not you’ve succeeded in properly applying your sunscreen is easy: “You know you’re applying your sunscreen properly if, after the first time you’ve used it, you haven’t gotten a burn,” Leffell says.

Agin has a caveat, though: "It’s not a good idea to think of sunscreens only as a way to extend your time in the sun," she says. "One must also understand that even before becoming sunburned, your skin is receiving UV exposure that causes other damage to the skin. At the end of the 600 minutes, you will have accrued enough UV to cause a sunburn—one Minimal Erythema Dose or MED—but there is pre-MED damage done to skin cells’ DNA and to the skin’s supporting structure of collagen and elastin that is not visible and happens even before you sunburn. These types of damage can occur without sunburning. So you can’t measure all the damage done to your skin by only being concerned about sunburn."

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us atbigquestions@mentalfloss.com.

An earlier version of this post ran in 2014.

What's the Difference Between Ice Cream and Gelato?

iStock/Getty Images/zoff-photo
iStock/Getty Images/zoff-photo

'Tis the season for beach reads, tan lines, and ice-cold desserts. You know it's summer when going to the local ice cream or gelato shop becomes part of your daily routine. But, what exactly is the difference between these two frozen treats?

One of the key differences between the two is butterfat. While ice cream's main ingredients include milk, cream, sugar, and egg yolks, the secret to making gelato is to use much less cream and sometimes little to no egg yolk. This leads to a much smaller percentage of butterfat in gelato. The FDA rules say that ice cream cannot contain less than 10 percent milkfat (though it can go as high as 25 percent) while gelato, much like soft serve, stays in the 4- to 9-percent range.

The churning method for both also differs, which affects the treat's density. Ice cream is churned at a much faster pace, leading to more air being whipped into the mixture. Ice cream's higher butterfat content comes into play here—due to all of that milkfat, the mix absorbs the air more readily. Gelato, on the other hand, is churned at a slower pace and absorbs far less air, creating a much denser dessert.

You also might have noticed that the serving style for the two treats aren't the same, either. In order to get those perfectly stacked ice cream scoops on a cone, buckets of ice cream must be stored at around 0°F to maintain its consistency, while the softer gelato is stored at a warmer 10°F to 22°F. Ice cream is then scooped into fairly uniform balls with the round ice cream scooper, whereas a spade or paddle is best for molding gelato into mound in a cup or a cone.

You can't really go wrong with either gelato or ice cream on a sweltering summer day, but there is one more difference to keep in mind while you debate which to get: taste. If you want a bolder flavor, you'll want to go with gelato. Because of the density of the cream and because there's less butterfat to coat your taste buds, gelato can seem to have more intensity to its flavors.

Have you got a Big Question you'd like us to answer? If so, send it to bigquestions@mentalfloss.com.

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