Pain and the Brain

Fresh pain is bad enough.  But at least when you wear ridiculous shoes or head-butt a door, you know you kinda deserve it. Old pain, though, when you can’t remember what caused it in the first place, well, that’s just not right.

The problem is that for all the wonderful things our brain does, it has a hard time forgetting pain.  In fact, research shows that any pain lasting more than a few minutes leaves a trace in the nervous system.

Which is why we should give a round of applause–gently, please–to a team of researchers at McGill University in Montreal who say they’ve discovered how to wipe out those unpleasant memories. They knew that because of the traces left behind, people with chronic pain often develop a hypersensitivity to more pain or even a touch. They also knew that a protein enzyme called PKM-zeta plays a critical role in building and maintaining memory by strengthening connections between neurons. So they set out to see if the PKM-zeta was responsible for pain memories and if they could erase them by blocking its activity at the neuron level.

This is where lab rats enter the picture, but in this case, so do chili peppers. That’s right, chili peppers, or more accurately capsacin, the compound that makes them burn. The scientists applied capsacin to the rats’ back paws, giving them a chemical  hot foot. And that’s when they discovered that PKM-zeta built up in the animals’ central nervous systems. Then, after applying to the rats’ spinal cords a chemical known as ZIP– which has been shown to stop the brain from holding on to memories–they found that the paws were no longer sensitive. The pain memory had gone away.

Or as Terence Coderre, the neuroscientist who headed the research put it: “We were basically able to erase it after the fact.”

We’re still a long way off from ZIP becoming a pain treatment. Obviously, a lot hurdles would need to be cleared, such as how do wipe out only pain memories without also losing recollections of your first kiss or the last time you got a great parking spot. But Coderre and his team have identified a target. And we’re a little bit closer to pain that truly is fleeting.

The sensitive sex

Men and women have been forever debating which sex can handle the most pain. I don’t have a winner for you–or loser, as the case may be–but there is more evidence that women have it worse.  A new study at Stanford found that even when men and women have the same ailments, women appear to suffer more.

This is based on analysis of the pain scores of 11,000 patients; invariably women rated their pain higher on a scale from one to ten. For instance, for joint and inflammatory pain, women patients averaged a score of 6.0 compared to 4.93 for men.  Overall, women’s pain levels were about 20 percent higher than men’s.

Now the easy explanation is that most men grew up learning to be stoic. I mean, what kind of tough guy would give himself an eight on any pain? But Dr. Atul Butte, the study’s lead author, believes that in a sampling this big, that wouldn’t be enough to explain such a significant variance in pain levels.

To believe Butte, it comes down to biology. Put simply, women and men experience pain differently.

Now resume the debate.

Pain, pain go away

Here’s other recent research on pain and how we deal with it:

• An even heavier weight: Analysis of  the responses of more than 1 million Americans in phone surveys reinforced the belief that obese people are more likely to be in physical pain. Researchers at Stony Brook University found that people they determined to be overweight or obese were much more likely to say they’d felt pain within the past day.
• When pain is good for you: While women appear to feel more pain, that’s often not the case when they suffer heart attacks. A new study concludes that women, particularly younger women, are less likely than men to feel chest pain when they have an attack.
• You’ll also develop a powerful attraction to flies: Johnson & Johnson has entered into a partnership with the University of Queensland in Australia to develop a medicine for chronic pain from spider venom.
• And you thought it was the crying baby causing the headaches: Research at the University of California at San Francisco found that women who suffered migraines were more than twice as likely to have colicky babies.
• Music soothes more than the soul: A recent article in The Journal of Pain (sign me up!) reported on a study at the University of Utah where subjects who were shocked on their hands felt less pain when they concentrated on music that was playing.

Video bonus: Naked mole rats are weird little creatures. But they can teach us a thing or two about pain.

Randy Rieland | | READ MORE

Randy Rieland is a digital media strategist and contributing writer in innovations for Smithsonian.com.