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Unique ‘Pain Fingerprint’ – New Study Charts Brain’s Varied Responses to Pain

pain fingerprint study illustrated by backyard brains
Illustrated by Cristina Mezuk

“How bad does it hurt?” It’s not for nothing that doctors usually struggle to ascertain our level of pain. It depends not only on how bad we report it to be, but also on the amount of pain we think we feel.

But are there reasons behind it that would begin to decipher our (in)ability to cope with or even verbalize the dreaded sensation? According to a recent collaborative study led by Dr. Elia Valentini from the University of Essex, there’s more to this phenomenon than a mere lack of tools that would accurately quantify exactly how much pain there is in an “ouch.”

What Does Our Brain Do While We Hurt?

So far, science held a more or less persisting view that a surefire way to quantify our levels of pain – much like any other physical sensation or state – was to measure our brain’s electrical activity. When you’re sitting and idly scrolling on your phone, your brain waves will likely hover around 12 Hz. Start dozing off and these alpha waves will slide back in intensity to theta (4-8 Hz) or even delta (1-4 Hz) if you were to fall asleep.

Sleeping brain EEG

But if a very angry tweet kicks you out of your zen, your brain waves are likely to surge into the beta sphere, anywhere from 22 to 38 Hz. Finally, if you hop into the kitchen and stub your toe on the way, your brain activity will shoot through the roof and exhibit a very high level of oscillations, up to 80 Hz.

Or so the theory went!

The study published in the Journal of Neurophysiology paints a more nuanced picture. Different brains, it suggests, show remarkably varied responses to the same type and amount of pain. This leads the researchers to believe that each of us have our own and unique “pain fingerprint.” To gauge what our brain does against what it says it does, the researchers took two groups of willing subjects and put them through two datasets. The first group of willing participants was zapped with a laser and touched within a 2-week span, whereas the other only only got the laser stimulus. All the while, the participants’ response was measured on two fronts. Their EEG was recorded with a focus on the rapid gamma brain waves. Three seconds after the stimulus was applied, the participants were asked to verbally rate their feeling of pain from no pain (0) to maximum pain they were willing to tolerate (10).

The most intriguing finding? We may experience and describe a stimulus as painful in a certain way and to a certain extent, but the gamma waves will not necessarily play along. In other words, the waves that have been associated with pain for so long will actually vary significantly between individuals. But where they do show in an individual, they will be remarkably stable, consistent and reproducible.


Beyond Silence: Plants Let Out Clicking Sounds When Thirsty or Hurt, Study Shows

Illustration of a plant letting out clicking sounds when thirsty or hurt
Illustrated by Cristina Mezuk

In a world of secrets, plants are speaking up. And science is all ears! As a recent study from the Cell journal shows, our leafy friends make popping or clicking sounds when under duress – such as when they are thirsty or injured.

But how exactly do plants make sounds? A team of scientists from Tel Aviv University led by Prof. Lilach Hadany decided to find out by placing tomato and tobacco plants in a soundproof box, as well as grapevine and wheat in a greenhouse. They used a device that can pick up very high-pitched sounds that are beyond the range of human hearing but seem to be just fine to field critters and other plants. To them, it may encode and transmit information about the plant’s condition and needs.

To be sure, a certain amount of vocalizing is normal in plants, as the scientists discovered. A happy plant that isn’t deprived of sustenance and isn’t experiencing any physical harm will make one such sound per hour on average. Cut it, and it will let out in between 15 and 25 sounds per hour. Dry it out, and the distress signals will bump up to 35 sounds per hour! Even more interestingly, not all of these sounds were created equal. Their quality varies depending on not only type but also the amount of stress. To sort them out and classify, the researchers resorted to machine learning models which, after being trained, managed to correctly “translate” the signals with up to 81% accuracy.

plants clicking sounds
Cactus plant with Microphones. Credit: Tel Aviv University

But what could be the purpose of this clickety fuss? Moths or mice, for example, can detect the hubbub within the 3-5-meter radius. In communicating with them, the plants are exhibiting a behavior that we humans can’t help but call altruistic. To a moth looking for a perfect green host to lay its larvae on, this signal may convey, for example, that a particular plant is in bad shape and not very likely to survive. But it’s not just rodents or insects that this botanical racket could be aiming at. Other plants may also be able to “hear” and interpret it as a distress call, a Morse code of sorts – and do what they can to adapt and survive dry spells in response.

However, that doesn’t mean that sound is the only communication channel in the plant kingdom. Earlier studies have shown that plants emit volatile organic compounds (that is, scent molecules) when they are thirsty or being munched on by an animal. Not to mention quirky responses to tactile stimuli as shown by the likes of Venus Flytrap or Mimosa Pudica that we at Backyard Brains have been researching. (And you can too!)

Social dynamics of plants and animals aside, what lesson is in it for us? And how can we put these findings to good use? This breakthrough, the researchers theorize, has a potential to revolutionize plant monitoring techniques, enabling farmers and gardeners to assess the well-being of their crops and intervene promptly if their plants are thirsty or besieged by pests. “We believe that humans can also utilize this information, given the right tools – such as sensors that tell growers when plants need watering. Apparently, an idyllic field of flowers can be a rather noisy place. It’s just that we can’t hear the sounds,” says prof. Hadany. But it’s not just about the plants’ trials and tribulations. Watering plants exactly where and when they need it can cut water waste by half while also increasing the yield.

In other words, when plants say they are thirsty or unwell in an era of precipitous climate change, the least we should do is – listen.

Comb Jellies take on 150 years of the Neuron Doctrine

When it comes to the nervous system, you might think we’ve got the basics down. After all, it’s been over a century since the great Santiago Ramón y Cajal proposed the neuron doctrine, which basically said that the nervous system is made up of individual, discrete cells called neurons. As you may recall from our neuropharmacology experiments, Ramón y Cajal argued for discrete cells (neurons), while Gogli thought that the brain consists of groups of continuously connected cells (reticulum). Santiago’s hypothesis, known as “The Neuron Doctrine,” was later confirmed by the invention of the electron microscope, which let us see these neurons and their connections in all their glory.

But now it looks like the fight is still on! New research on ctenophores, those weird, squishy marine critters that look like a cross between a jellyfish and a feather duster, is shaking up the status quo.

The importance of these jellies cannot be overstated. As one of the first animal groups to branch off on the evolutionary tree, studying ctenophores can provide us with clues about the very origins of animal life. And while these guys have no brains, they do have a nervous system consisting of a “neural net” – a type of nervous system organization that is very understudied. Could it be that a nervous system evolved twice, independently, in our animal ancestors? That’s the question these researchers were asking.

To get their answers, a group of European researchers led by Dr. Kittelmann at Oxford Brookes University turned to high-pressure freezing-fixation techniques and a method called serial block face scanning electron microscopy (try saying that five times fast!). This gave them a stunning, 3D view of the ctenophore’s nerve net. And what they found was quite unexpected and they shared it with the world in a recent Science paper [Burkhardt et al., Science 380, 293–297 (2023)].

Unlike our own nervous system, which comprises separate neurons connected by synapses, the ctenophores’ nerve net looked more like a reticulum – a continuous network of interconnected cells. Instead of discrete neurons with synapses (small gaps between the cells), the ctenophores have a nerve net where all the nerve cells seem to be part of one, big supercell. It’s kind of like comparing a bunch of individual houses to a giant apartment complex. As seen in their figure below, the 5 separate neurons of the nerve net are actually all fused together (highlighted in white asterisks for links between neuron 1 and 2).

Neural Net with connections

In the world of nerve nets, this is a pretty big deal, as it suggests that there’s more than one way to build a nervous system and that different animals might have taken different paths in their evolution to encode information and guide behaviors. The ctenophore nerve net is not just a simple precursor to our own complex brain but a complex and unique structure in its own right.

This opens up a whole new perspective on how nerve nets and nervous systems function and evolve, and reminds us that even long-held truths in science can change upon new evidence. So next time you see a ctenophore, don’t just marvel at the beauty of the squishy color-changing blob. You can also admire its nervous system that’s every bit as complex and fascinating as ours, just in its own, unique way. And who knows? Maybe we’ve got more in common with these jellies than we think. There’s so much more to be discovered!