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August 28, 2015

Why Do We Feel 'Pins and Needles' When our Appendages Fall Asleep?

This is the latest post in my #BrainBits series, where I'll answer your burning neuroscience questions in 60 seconds or less. If you have a question you'd like me to answer, you can e-mail me, tweet me, or submit your questions anonymously here.

Medical Treasure
Why do we feel "pins and needles"?  We've all experienced the strange sensation. Maybe it's when your alarm goes off in the morning and you realize you can't feel your arm to shut it off. Or when your legs are folded into a pretzel on the floor while playing Barbie with your kid and you can't stand back up. You give your dead appendages a shake, and suddenly you feel a surge of pins and needles. What causes that feeling?

There's actually a medical term for it  – paresthesia – defined as the tingling sensation caused by pressure or damage to peripheral nerves.

Don't pinch these! Gray's Anatomy
(Wikimedia Commons)
It occurs when there's prolonged pressure on a limb, like your arm positioned awkwardly under your head while sleeping or sitting cross-legged on the floor. The limb "falls asleep," either due to (1) arteries being compressed, thus blocking blood flow of oxygen and glucose to feed the nerves, or (2) directly pinching nerve pathways, causing normal neurotransmission to slow or cease.

Although your limbs may feel lifeless, your brain is receiving a signal of pain, saying "change your position already, idiot!" When you finally free your limb, the sensation of pain intensifies as blood returns to the area and nerves begin firing regularly. The "pins and needles" sensation occurs as certain areas nerve fibers receive blood nutrients and begin re-firing before others. Eventually, after a few seconds, equilibrium is established again.

A common misconception is that blood flow is blocked entirely to the affected limb when it "falls asleep." If that were true, we'd be experiencing a much more serious medical problem. Luckily, the 50,000-60,000 miles-worth of capillaries in our bodies ensure that our other tissues stay satiated and healthy. It would be as though a tourniquet were applied to a limb, and that's simply not what's happening.

Prolonged, regular compression to nerves can result in a more long-term sensation of "pins and needles," such as carpal tunnel syndrome. Consult a doctor if pain, tingling, and numbness is not relieved when you change body position.

Now, I'm going to undo my leg from under me (as I always do when I write) and go for a short walk to wake it back up. OUCH. Sometimes I never learn.

Stay tuned for next week's #BrainBits: "What the heck is déjà vu? Why do I get it and some people never do?"

August 12, 2015

Why Do I Get Hangry (Angry When Hungry)?

This is the latest post in my #BrainBits series, where I'll answer your burning neuroscience questions in 60 seconds or less. If you have a question you'd like me to answer, you can e-mail me, tweet me, or submit your questions anonymously here.

Niklas Hellerstedt (Flickr)
Why do we get hangry?  One lovely fall day a few years ago, my now-husband (I'm not sure why he married me after this) almost left me on the side of the road. We had just left a Penn State football game, and I was H-U-N-G-R-Y.

My resulting behavior was far from what you might consider "ladylike," much less "civilized." I won't even re-type the words that were spoken. Eventually, a pit stop for a burger and fries managed to tame my inner beast.

What causes the sensation of "hanger" – the phenomenon of feeling angry and short-tempered when hungry? Coincidentally, fellow The Conversation writer and obesity/nutrition researcher Dr. Amanda Salis recently covered this topic here. Do check out her article for details, as I'll be mostly summarizing below.

Basically, three major factors are thought to contribute to our bad tempers when we're famished:

Glucose metabolism. Mikael Häggström (Wikimedia Commons)
1. When we eat, carbohydrates are broken down into simple sugars, one of which is glucose. Right after a meal, the levels of glucose in our blood are high. Over time, though, blood-glucose levels drop. Eventually, if these levels fall far enough, your brain will perceive it as life-threatening. Unlike other organs, which have an energy back-up, your brain relies solely on glucose as a fuel source and requires a continuous supply. In fact, despite accounting for only 2% of your body's mass, your brain is estimated to use up 20-23% of your body's energy intake throughout the day, even at rest. Low blood glucose, obviously, signals, "imminent death! Act now!"

2. To our other organs, low glucose ramps up hormones that act to increase glucose in the body. Among these are epinephrine and cortisol, which are synthesized in the adrenal glands. These are both stress hormones, released when our body perceives threat, like a lion chasing us or an organic chemistry exam being handed out in class. That's enough to change someone's mood for the worse, right?

3. As it turns out, anger and hunger don't only share many of the same letters, but they're also controlled by similar genes. One of these genes produces a protein called neuropeptide Y, which not only stimulates eating behavior, but also regulates anger and aggression. Long story short, I probably had pretty high levels of neuropeptide Y after that football game.

What about you?
Do you get hangry, too?
Let us know
In this anonymous poll!

Stay tuned for next week's #BrainBits: "Why do we feel 'pins and needles' when our appendages fall asleep?"