Tag Archives: nervous system

What is pain, and why do we even need it?

Arguably the least enjoyable sensation out of them all, pain always demands attention — and a reaction. But why would biology even give us the ability to feel such a debilitating sensation? Why can’t we just block it out by ourselves? Why even have it in the first place?

Image credits Dimitris Vetsikas.

Pain is unpleasant by design. It needs to be because it is our body’s alarm system. It warns us whenever some bit isn’t functioning correctly, of issues such as disease or infection, and of damage and injury. But, and this is a very important but, it doesn’t always do that. People can feel phantom limb pain even after having a limb amputated. Injuries can be sustained without any feelings of pain, either temporarily or permanently. Our brain can completely block it out if needed. And things such as loud or high-pitched noises can cause us pain without producing any injury (although they can cause these too).

It also “pains us to say this” sometimes. We all know that it’s a figure of speech, especially in work emails, but is there any literal truth behind that?

First off, what is pain?

From our direct experience of it, it’s easy to start seeing pain as punishment — scratch your knee through carelessness, then it starts hurting to get revenge. In actuality, however, pain is meant as a behavioral corrector. Research in the field showed that it doesn’t have to be produced by tissue damage, but rather works as a preventative as well as a protective mechanism. It is so unpleasant and hard to ignore because it was designed from the ground up to get your attention, hold it, and make you want to make it stop.

We all intimately know that pain is an unpleasant, physical sensation. But its current definition also includes its emotional component, meaning that pain can also be a feeling or a constellation of feelings associated with actual or potential harm.

Image via Pixabay.

Physical pain is handled by specialized nerve endings called nociceptors running through and across our bodies. These stay alert for any change that could pose a risk for us, including changes in temperature, chemistry, or pressure. The signals they send to our brains once dangerous thresholds are passed are interpreted or perceived by us as pain. For example, getting bitten hurts because the pressure being applied in that area is almost as great, or greater than, what our skin can safely handle. Keeping your palm on a block of ice for too long starts hurting because it prevents our tissues there from keeping their normal temperature.

Feelings of pain can also be neuropathic in nature (related to damage incurred by the nervous system) or nociplastic (produced by changes in our pain thresholds, generally without injury). The former is the kind of pain you perceive as burning, tingling, or stabbing in your fingers. Diabetes patients often develop long-lasting neuropathic pain, most commonly felt as severe burning pain at night, due to nerve damage incurred by the disease.

It is important to note that like pretty much every other one of our senses, pain doesn’t actually exist, it’s simply a product of our brains. The most concrete manifestation of pain would be the electrical impulses sent out by nociceptors when certain conditions are met. The actual unpleasant sensation you feel, however, is just something your brain creates as it deems necessary. It looks at information such as what threats are present (as informed by our senses), our cognitive state, previous experience with certain types of stimuli, social and cultural norms, and so on.

In other words, when a certain part of you is injured or just not having a good time, it doesn’t hurt; your brain makes you think it hurts. That pain is meant to encourage you to keep said area safe and protected so it can heal. You’ll know how to do so because it will hurt more whenever you don’t. It’s a pretty straightforward system like that.

How we feel it

One thing that I feel is important to note here is that the nerves in our bodies are not made equal.

The nerves in your body are meant to (and are thus specialized to) feel certain kinds of pain in certain ways. For example, the nerves running through your internal organs will readily pick up on distension (stretching), ischemia (reduction in blood flow), or inflammation, beaming these back to you as a diffuse pain. This pain is not highly localized because you don’t really need it to be — all that matters is that you understand there’s something going on inside your belly and you should manage it.

What these visceral nerves are not good at, however, is feeling stuff like cuts or burns. The ones in your skin, meanwhile, are very good at picking up on these, and they’re also very good at pinpointing exactly where the pain comes from. It’s much more important to know where you got a cut on your skin so you can keep it clean and prevent infection, so your body supplies this information.

However, at the end of the day, all nerve fibers make their way to the same spinal cord. But because both areas with a higher sensory density (skin, for example) and those with low sensory density (such as viscera) end up here, their data can get scrambled up. This can produce an effect where pain from one low-sensitivity area can be interpreted as coming from a high-sensitivity area.

Types of pain

A pain management chart, meant to help patients more accurately describe the levels of pain they’re feeling. Image credits LPWaterhouse / Flickr.

The first one we’ll talk about today is ‘referred‘ or ‘reflected’ pain, that’s felt in one part of the body but produced by injuries in another. For example, a kidney stone will make your back hurt, and a stroke can make your jaw sore. Referred pain is produced because the nerve pathways serving the injured areas also connect to others, which may mess up where our brains perceive the pain (although we don’t yet have a good grasp on why it happens). There is also ‘radiating‘ pain, similar to the referred one, with the slight difference that the sensation is also felt in the area that has sustained an injury, not just away from it.

Acute pain is diagnosed mostly based on duration and re-emergence. If the pain can be resolved quickly it is considered to be acute. The exact definitions are still a bit blurry, and the time window used to determine acute pain has varied from 30 days to 6 months, even up to 12 months. One simple way to describe acute pain is that it doesn’t extend beyond the expected period of healing, or that it is short-lived.

On the other hand, we have chronic pain. This can last for years, even your whole lifetime, if you’re particularly unlucky. This can be produced by a variety of conditions, although doctors sometimes make a distinction between cancer-related and benign chronic pain. One easier way of describing it is as pain that extends past the expected period of healing, or that it is long-lasting.

Phantom pain sounds spooky, and it is. This is the type of pain individuals sometimes feel in a limb they lost through accident or amputation. Although a part of their body is gone, these individuals still feel (sometimes very significant) levels of pain in that limb. This is a type of neuropathic pain. It’s a very common symptom, occurring in over 80% of upper-limb amputees and over 50% of lower-limb amputees.

Breakthrough pain is often associated with cancer patients, but they’re not the only ones to experience it. Breakthrough pain is a ‘background’ pain that’s usually controlled by medication but sometimes ‘breaks through’ these in bouts of acute pain.

Finally, to your brain, emotional pain is almost the same as the physical kind; which is why breakups are so enjoyable.

How do pain blockers work?

Image credits Arek Socha.

Pain pathways form a very intricate system in our bodies. This is also by design: our ability to feel pain has to be reliable, because it’s meant to keep us alive.

However, our brains can block out pain when needed. If we find ourselves in a dangerous situation where tending to our wounds is not possible — when we’re facing a predator, for example — pain can become counterproductive. The sensation could limit our range of motion or willingness to move and fight in this scenario. As such, our brains temporarily block painful sensations to allow us to escape or prevail. You’ve probably also experienced getting injured during a tense or dangerous situation and only later noticing it. Adrenaline or states of shock can also block out the sensation of pain.

This process takes place without our input and isn’t reproducible at will. Still, having the ability to stop pain is very handy, so we’ve developed ways of doing so. Anesthetics or pain blockers work by either preventing nerve endings from transmitting pain signals to the brain, or in one way or another stopping the brain from producing a painful sensation.

General anesthesia, for example (the kind you’d get before surgery) disrupts nerve activity throughout your whole body. This prevents us from feeling pain while under anesthesia, and blocks our recollection of it afterwards. All the extra bits that come with general anesthesia — the specialized doctor who administers the drugs and monitors you, tubes to feed oxygen into your lungs, monitoring devices — are all there because anesthesia basically shuts down your nervous system. If not done properly, this can and will kill you, most commonly by breaking the communication lines between your brain, heart, and lungs.

There are four stages to general anesthesia — induction, delirium, surgery anesthesia, and overdose.

  • Induction starts when the drugs are administered, and lasts until you fall asleep. During this stage, you’ll still be able to talk and focus to some extent. However, your breathing will slow down, and you’ll slowly lose the ability to feel pain.
  • The delirium phase is quite dangerous, and an anesthesiologist will do their best to make it last for as brief a time as possible. This step takes place as the nerves connecting your body to your brain stop working properly, making bits of you act weird. The delirium phase can produce uncontrolled movements, irregular breathing, and can lead to an increase in your heart rate. It’s also possible to see patients vomit during this stage, which can be quite deadly (there is a significant risk of choking).
  • In the surgical anesthesia phase, things calm down a little. A patient’s eyes stop moving and their muscles relax completely. It’s very possible that a patient in this state is unable to breathe unassisted. This is the ideal state for surgery and the one an anesthesiologist will try to keep you in as it is the least dangerous stage apart from induction.
  • The overdose stage takes place if too much anesthesia is administered to a patient. It’s rarer nowadays, but it’s still a very dangerous event with a high risk of being fatal. The risks are related to the communication lines between your brain, heart, and lungs going completely silent. If a patient is not brought up fast enough, or his breathing and heartbeat not maintained artificially, he will die.

Local anesthesia is far less powerful, affects a much smaller, more controlled area, but it’s also less risky. The most reliable way to differentiate local from general anesthesia is that the former involves loss of pain sensation but not loss of consciousness — general anesthesia leads to a temporary loss of both.

Local anesthetics typically work by blocking certain biochemical pathways inside nerve cells in a certain area. Most commonly, they target sodium ion pumps on the membranes of cells. This effectively prevents those cells from sending signals to the brain, as the electrical signals our bodies rely on are mediated by ions zipping here and there over nerve cells.

Psychological pain

Image via Pixabay.

The muddier and arguably worse type of pain, psychological pain can be summarized as ‘suffering’. It’s also referred to as emotional or mental pain, and is usually described as a deeply unpleasant but hard to delineate feeling.

Since people are complex creatures, psychological pain is hard to define in concrete terms. It encompasses a wide range of feelings and subjective experiences produced by the awareness of negative events or changes in one’s life, abilities, bodily functions, social standing, and so forth. Perceived shortcomings or deficiencies in the self can also lead to psychological pain. Losing a loved one is a major cause of psychological pain and, for better or for worse, an inescapable part of being human.

Being a deeply subjective experience, psychological pain is much harder to discuss in concrete terms. One of the most commonly used definitions of psychological pain today is that it is caused by our unmet psychological needs (making it the opposite of happiness). Unlike physical pain, it is most often described as being a diffuse sensation without necessarily having a known cause, is seen as generally long-lasting, and as having an adverse effect on the self and our ability to function.

Art has long grappled with themes of suffering, emotional distress, how these impact us, and it may be, in many ways, one of our most efficient tools in learning how to deal with psychological pain on a personal level. Therapy also works wonders. You can mix and match them if you need to.

To wrap things up

Pain, to hold to the definition we started this journey with, is meant to help correct our poor behavior — i.e. do things that hurt your body then feel pain, so, hopefully, you’ll stop doing the bad thing. Psychological pain, then, can also be seen as a way to correct our poor behavior in the social or cognitive realm.

This gives pain, and especially suffering, a strange double nature. They both are supremely unpleasant to us, but they are also great teachers. People will go to great lengths to avoid pain, which shows just how great this feeling is at correcting behavior. In fact, Freudian psychology considers the ability to endure pain now for a worthy outcome (delayed gratification) as the hallmark of maturity, as we don’t really have free will until we can face the fear of pain and overcome it (the pleasure principle vs reality principle).

People have recognized this nature for millenia now. The oldest stories we know of, such as the Epic of Gilgamesh, the Iliad, or creation myths around the world, delve deeply into experiences such as loss of a loved one and/or rebirth, loss of social standing and power, of being far away from home unable to return. Characters, be they mortals or gods, are shown to pass through suffering and emerge anew on the other side — sometimes stronger, sometimes weaker for it. Others, like Darth Vader for example, try and fail to overcome their suffering, and become defined by it until they succeed. Those are the kinds of stories that still captivate us because we can all understand and have experienced psychological pain, and desire to see our heroes and villains overcome it and get their due.

I’ll end with a quote from Fyodor Dostoevsky, a titan of the Russian novel, that I feel perfectly encapsulates humanity’s unique relationship to pain. Dostoyevsky started his adult life as an idealistic, passionate political reformist. A religious awakening after a mock execution and a real sentence in a Siberian labor camp (he was a very interesting guy) led him to a captivation with how the human ‘soul’ (in his words) or psychology (in modern parlance) works. His writing is very good, if at times disjointed (he was suffering from a particularly debilitating form of epilepsy), so go read them if you like exploring new depths of despair. But until then I leave you with this quote from his 1864 book Notes from the Underground:

“And why are you so firmly, so triumphantly, convinced that only the normal and the positive — in other words, only what is conducive to welfare — is for the advantage of man? Does not man, perhaps, love something besides well-being? Perhaps he is just as fond of suffering? Perhaps suffering is just as great a benefit to him as well-being?”

“Man is sometimes extraordinarily, passionately, in love with suffering, and that is a fact.”

New study highlights vitamin E’s essential role in brain development

Researchers at the Oregon State University say that vitamin E may be more important in embryo development than we assumed.

Image credits Kevin McIver.

The study reports that embryos of vitamin E-deficient zebrafish develop malformed nervous systems, including their brains. Although the findings are based on animal models and may thus not perfectly translate over to humans, they can help guide our research into the topic. In the end, it could help us better understand the biochemical mechanisms behind pregnancy and maintain the health of embryos in the womb.


“This is totally amazing — the brain is absolutely physically distorted by not having enough vitamin E,” said Maret Traber, a professor in the OSU College of Public Health and Human Sciences.

Zebrafish are a common model animal used for biological research. They’re a species of small freshwater fish that need about five days to develop from a fertilized egg into a young individual. This short period makes them ideal for studying the development and genetics of vertebrates. They’re also easy to care for, which helps.

The link between vitamin E — or “alpha-tocopherol” — and embryo development was first identified in 1922 (this link is what led to the discovery of the compound), when it was noted that vitamin E is essential for the successful development of pregnancy in rats. However, we didn’t know why this was.

“Why does an embryo need vitamin E? We’ve been chasing that for a long time,” said Traber. “With this newest study we actually started taking pictures so we could visualize: Where is the brain? Where is the brain forming? How does vitamin E fit into this picture?”

The team explains that the development of the zebrafish’s nervous systems starts with a brain primordium and a neural tube. These go on to develop and innervate (send nerve bundles) throughout the body. If deprived of vitamin E, these embryos show defects at the level of the brain and neural tube. The team’s photographs show that vitamin E acts “right on the closing edges of the cells that are forming the brain,” which are called neural crest cells.

These cells act like stem cells and are involved in the formation of the bones and cartilages in our face, and also spread from the brain to create nerve bundles. They end up forming cells and tissues in 10 different organ systems, the team adds.

“By having those cells get into trouble with vitamin E deficiency, basically the entire embryo formation is dysregulated. It is no wonder we see embryo death with vitamin E deficiency,” Traber explains.

In the experiment, embryos who developed lacking vitamin E lived to a maximum of 24 hours and then died. The differences between them and control embryos were first noticeable at around the 12-hour mark but weren’t yet fatal.

Vitamin E is actually a group of compounds with similar chemical structure. One of them, alpha-tocopherol, is what’s commonly and commercially referred to as ‘vitamin E’ in the European Union, while gamma-tocopherol is the type most commonly seen in the US. They’re most commonly found in oils and oily foods such as hazelnuts, sunflower seeds and avocados.

“Plants make eight different forms of vitamin E, and you absorb them all, but the liver only puts alpha-tocopherol back into the bloodstream,” said Traber. “All of the other forms are metabolized and excreted. I’ve been concerned about women and pregnancy because of reports that women with low vitamin E in their plasma have increased risk of miscarriage.”

The paper “Vitamin E is necessary for zebrafish nervous system development” has been published in the journal Scientific Reports.

You don’t need a brain to learn, scientists found

A new study from the University of Toulouse found that intelligence and learning aren’t limited to organisms with brains. By studying the mold Physarum polycephalum¬†they found it can, over time, learn to navigate even irritating environments.

Physarum polycephalum.
Image via flikr user frankenstoen.

People have been arguing for ages on exactly what “intelligence” is. For some,¬†it’s reflected in academic results, so intelligence can be measured by how well you can solve a math problem for example. Others think of it as the basis for flexibility and adaptation, and for them, one’s intelligence is measured by how well they perform when faced with novel and unfavorable conditions. Or it could be emotional intelligence, musical intelligence, the list goes on. All of these definitions, however, start from the assumption that intelligence is a product of the brain’s ability to rely on past experience to interpret present events. That’s just not true.

On Wednesday, scientists announced a discovery that turns this basic assumption on its head. A new study of Physarum polycephalum, the “many-headed slime,” found that this mold can learn about its environment despite lacking any type of central nervous system. This is the first demonstrated case of habitual learning in a brainless organism.

“Tantalizing results suggest that the hallmarks for learning can occur at the level of single cells,” the team wrote.

Habitual learning is the process through which behavior is altered as a response to repeated stimulus. Similar to physical adaptation — how calluses form on a guitarist’s fingertips to adapt to their pressing the strings over time — habitual learning is learning by doing. It’s what allows you to walk or drive or talk without you having to put too much mental effort into it. In more extreme circumstances, it helps people with phobias overcome the object of their fear through gradual but repeated exposure to it.

P. polycephalum cells merge into a single yellow blob when food becomes scarce and has previously shown a type of proto-memory in navigating its environments (and there are other examples of cells banding together in rough times or cellular memory that we’ve previously covered.) The Toulouse University team wanted to see if it could also learn from experience and alter its behavior in response.

This slime-blob grows fine root-like protrusions called pseudopods to move through its environment as it searches for food or shade. The team grew slime samples in petri dishes containing a gel made of agar, and placed these near other petri dishes with food — oatmeal in agar gel. The dishes were connected through a bridge of agar gel, which the mold would learn to crawl over to feed in about two hours. The researchers then coated this bridge with quinine or caffeine in concentrations that weren’t toxic but P. polycephalum found irritating.

The blob creates filaments in search of food.

At first, they note that the mold “showed a clear aversive behavior” — it halted for a short time, then started advancing at a much slower pace. Overall, it took more than three hours for the pseudopods to cross the bridge, seeking narrow paths to avoid the irritating substances. But as the days passed the mold overcome its initial reticence and started crossing much quicker, evidence that it had “habituated” to the quinine and caffeine, the team said — in essence, it learned to navigate through unfavorable environments.

“Our results point to the diversity of organisms lacking neurons,” they wrote, “which likely display a hitherto unrecognized capacity for learning.”

The findings suggest that life could learn way before it developed any type of nervous system. This discovery could offer us new insight into the behavior of other molds, even viruses and bacteria.

The full paper, titled “Habituation in non-neural organisms: evidence from slime molds ” Has been published online in the journal Proceedings of the Royal Society B and can be read here.

Ant colonies behave as a single superorganism when attacked

Ant colonies are incredibly complex systems — the tightly knit, intensely cooperative colonies are closer to a single superorganism than to human societies. Researchers form the University of Bristol wanted to know how this single mind of the hive reacted to distress, and subjected colonies of migrating rock ants to differing forms of simulated predator attack to record their response.

Led by Thomas O’Shea-Wheller, the researchers subjected ants to simulated predator attacks to investigate the extent to which colonies of rock ants behave as a single entity.
Image via phys

By studying the ants responses, the team observed different reactions depending on where the attack was performed. When targeting scouting ants, that stay primarily at the periphery of colonial activity, the “arms” of foraging ants were recalled back into the nest. But when they targeted the workers at the heart of the colony, the whole body of ants retreated from the mound, seeking asylum in a new location.

The team was able to draw some pretty interesting parallels with human behavior. The first attacks could be compared to burning your hand on a hot stove, while the ones centered on the workers were more dangerous, kind of a ‘house on fire’ scare. And in each scenario, the ants reacted surprisingly similar to any animal with a nervous system — an involuntary reflex reaction to retreat from the damaging element in the first case, and a flight response from a predator that can’t be defended against in the later simulations.

“Our results draw parallels with the nervous systems of single organisms, in that they allow appropriate, location dependent, responses to damage, and suggest that just as we may respond to cell damage via pain, ant colonies respond to loss of workers via group awareness,” said Thomas O’Shea-Wheller, a PhD student in Bristol’s School of Biological Sciences and one of the authors of the study.

Brainless slime redefines intelligence, could solve real problems

Single cell amoebae can remember, make decisions and anticipate change, urging researchers to redefine what we perceive as intelligence as soon as possible.

For gardeners, they are usually a pest, for some hikers, a nice view, and for researchers, they are protists, a taxonomic group reserved for “everything we don’t really understand,” says Chris Reid of the University of Sydney. The big mystery here comes from the fact that slime molds are much more intelligent than they seem at a first glance.

As we told you in a previous article, these creatures can navigate using external memory, despite having no brain. Particularly one species, yellow Physarum polycephalum, can solve mazes, mimic the layout of man-made transportation networks and choose the healthiest food from a diverse menu – again, all of this without a nervous system.

The maze solving was just the first sign of intelligence, basically ringing a bell that something’s really going on down in slime. But then researchers did something way different: they placed food in the relative positions of the major cities and urban areas, the slime accurately recreated the railway of Tokyo, as well as the major railways of England, Canada, Spain and Portugal. The cell solved a real world problem which took teams of engineers and urban planners to solve – making scientists believe that with further studies, the slime could have some real life problem solving importance.

But P. polycephalum is not only a great navigator and good forward thinker, but it’s also a healthy eater. Their ideal diet comprises of two thirds protein and one third carbohydrates. Audrey Dussutour of the University of Paul Sabatier in France placed slime molds in the center of a clock face of 11 different pieces of food, each with a distinct ratio of nutrients. Almost every time the slime would go for the optimal diet – something you can’t say for most people today.

So how do they do it? How do they memorize, how to they analyze the nutrient ratio, how to they find the optimal solution to a presented problem? Well… we don’t know. Several hypotheses have been proposed, but none has solid evidence to back it up. But slime molds are definitely magnificent creatures; they evolved somewhere between 600 million years ago and one billion years – no organisms had nervous systems then, yet they found a way to memorize, analyze and predict – they found a successful and admirable alternative to convoluted brain centered intelligence; one could say they break the mold.