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How Does Scratching Relieve an Itch?

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If you have an itch, you scratch it. Scratch and itch; they go together like peas and carrots and everyone—humans, apes, dogs and cats—knows it. What we didn't understand for a very long time was the physiological connection between the two—why a good scratch relieves a bad itch.


A study by a group of neuroscientists at the University of Minnesota recently explained the itch-scratch link.* The group hypothesized that the relief mechanism doesn't take place along the nerves of itchy skin, as had been thought, but deep in the central nervous system, in the same area that the itches themselves are communicated. Previous studies showed that neurons in the spinothalamic tract (STT)—a sensory pathway originating in the spinal cord that transmits information about pain, temperature and touch to the thalamus—were activated with the application of itch-inducing chemicals, and these are the neurons that send itch sensations to the brain.

In the new study, the UM researchers implanted recording electrodes in the spinothalmic tracts (STT) of macaques monkeys (the STT is at the base of the spinal cord; most STT neurons respond to pain and some to both pain and itch). Then researchers injected itch-inducing histamines into the monkeys' legs and watched as the STT neurons fired. They then scratched the monkey's itchy legs with a device that mimicked the feel of monkey fingers, and the firing rate of the STT neurons dropped rapidly.

The sudden drop, the researchers said, is the neurological equivalent of the relief you feel after a good scratch, indicating that itching and relief sensations are both rooted in the spinal cord and relief from an itch comes from inhibiting—via scratching—the STT neurons. Scratching basically tells all those tattle-tale neurons who are whining to the brain about an itch to just shut up already.

scratchingOf course, the itch and the scratch still hold plenty of mystery. When the team scratched the monkey's legs without first inducing an itch, the STT neurons fired in a normal response to stimuli, but the scratching didn't slow the firing.


Scratching also had no effect on neurons' response to an application of capsaicin, the spicy component in hot peppers. The STT neurons, it appears, react differently to the sensation of a scratch depending on whether an itch exists, and the nerve-dampening effect of scratching only works when the neurons are firing because of an itch, not pain. Somehow, the neurons know the difference. Itching isn't all physiological, either; it can be caused by emotional and psychological factors and can even be picked up as a "contagious itch" (a study showed that itching can be induced purely by visual stimuli: watching other people scratch).

Once all that is sussed out, though, the UM team's discovery could lead to ways of duplicating the end results and benefits of scratching (quiet, polite STT neurons) without its drawbacks. That's great news for people with the sorts of chronic itching associated with AIDS, Hodgkin's disease and the side effects of some pain medications. Chronic itching, of course, leads to plenty of scratching, which can lead to skin damage, infections and worse (remember the New Yorker article with the woman who scratched right through to her brain?)

* Davidson et al. Relief of itch by scratching: state-dependent inhibition of primate spinothalamic tract neurons. Nature Neuroscience, 2009; 12 (5): 544

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Health
8 Potential Signs of a Panic Attack
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It's not just fear or worry. In fact, many panic attacks don’t look like panic at all. Panic attacks come on rapidly, and often at times that don't seem to make sense. The symptoms of panic disorder vary from person to person and even from attack to attack for the same person. The problems listed below are not unique to panic attacks, but if you're experiencing more than one, it's a good idea to talk to your doctor either way.

1. YOU'RE DIZZY.

Doctors sometimes call the autonomic nervous system (ANS) the "automatic nervous system" because it regulates many vital bodily functions like pumping blood all on its own, without our having to think about it. Panic attacks often manifest through the ANS, leading to increased heart rate or decreased blood pressure, which can in turn lead to feeling lightheaded or faint.

2. YOU'RE LOSING YOURSELF.

Feeling detached from yourself is called depersonalization. Feeling detached from the world, or like it's fake or somehow unreal, is called derealization. Both forms of dissociation are unsettling but common signs that a panic attack has begun.

3. YOU'RE QUEASY.

Our digestive system is often the first body part to realize that something is wrong. Panic sends stress hormones and tension to the gut and disrupts digestion, causing nausea, upset stomach, or heartburn.

4. YOU FEEL NUMB OR TINGLY.

Panic attacks can manifest in truly surprising ways, including pins and needles or numbness in a person's hands or face.

5. YOU'RE SWEATY OR SHIVERING.

The symptoms of a panic attack can look a lot like the flu. But if you don't have a fever and no one else has chattering teeth, it might be your ANS in distress.

6. YOU KNOW THE WORST IS COMING.

While it may sound prophetic or at least bizarre, a sense of impending doom is a very common symptom of panic attacks (and several other conditions). 

7. BREATHING IS DIFFICULT.

The ANS strikes again. In addition to the well-known problems of hyperventilation or shortness of breath, panic attacks can also cause dyspnea, in which a person feels like they can't fill their lungs, and feelings of choking or being smothered.

8. YOU'RE AFRAID OF HAVING A PANIC ATTACK. 

Oddly enough, anxiety about anxiety is itself a symptom of anxiety and panic attacks. Fear of losing control or getting upset can cause people to avoid situations that could be triggering, which can in turn limit their lives. 

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Live Smarter
You Can Be a "Nonresponder" to Some Types of Exercise
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If you’re working out but don’t feel like you’re in any better shape, you might be a “nonresponder.” A study from Queen’s University in Canada finds that how people respond to exercise regimens varies substantially, and what works for one person may not help another person improve at all.

But that doesn’t mean those nonresponders will never get into shape. They just may need to change up their exercise routine for one that is better suited to their body. The study tested two exercise regimes on 21 active adults. Each of them spent three weeks doing endurance training (like running for an extended period of time) or interval training (doing quick bursts of strenuous exercise, like in CrossFit). After a few months of rest between workout periods, they then switched one routine for the other. Endurance trainees rode a stationary bike four times a week for 30 minutes, while high-intensity interval trainees did 20 seconds of hard pedaling on the bike with a 10 second rest after each interval.

Some of the participants showed improvements in physiological markers of fitness like heart rate and oxygen capacity after one of the workout periods, but others didn’t improve at all. Some were even in worse shape than before they began their assigned regimen. However, each individual responded to one of the workouts, even if they didn’t see results in the other.

To figure out which workout works for you, you’ll need to measure your fitness levels, using your pulse as your baseline number, at the beginning of a new workout routine. Then, after a month of either endurance or interval training, you should check to see if you've made improvements in your heart rate, according to the Times. If you haven't, you should switch to another routine.

[h/t The New York Times]

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