Sometimes we think how good it would be if we didn't feel pain. Maybe would we felt like a heroes? Or invincible? Or as can The Rock? Wrong. Getting rid of pain can to be lucky but that’s not good. 12-year-old “Thomas” It’s a boy that never felt deep pain, not even when fractured your leg. Not only did he feel no pain as he continued walking without know with one leg shorter than the other and he ended up slowly crushing his right knee joint (Minde, (2004)). Life without pain is a harsh reality because of a mutated gene that affects the growth of the nerves conducting deep pain. Most of those affected suffer from joint damage and frequent fractures to bones in their feet and hands, some end up in wheelchairs even before they reach puberty. It turns out pain generally serves us well. Living without a sense of touch sounds less attractive than live with pain, touch is a source of pleasure and essential to how we feel. Losing the sense of touch has severe implications.
When holding your friend’s hand, you feel the heat from their skin, the softness or roughness of their palm, and the pressure from their fingers. The sense of touch conveys important social information, helping strengthen bonds between people. If your friend grips your hand so hard it hurts, touch lets you know something is wrong or dangerous through the feeling of pain (Blumenrath, BrainFacts.ORG, 2020).
Sensations begin as signals generated by touch receptors in your skin. They travel along sensory nerves made up of bundled fibers that connect to neurons in the Spinal Cord.
Remembering that Spinal Cord is a cylindrical structure that runs through the center of your spine, from your brainstem to your low back. It's a delicate structure that contains nerve bundles and cells that carries nerve signals from your brain to your body and vice versa. These nerve signals help you feel sensations and move your body. Any damage to your spinal cord can affect your movement or function (professional, Clevelend clinical, 2021).
Your spinal cord’s main purpose is to carry nerve signals throughout your body. These nerve messages have three crucial functions. They:
· Control body movements and functions - Signals from your brain to other body parts control your movements. They also direct autonomic (involuntary) functions like your breathing rate and heartbeat, as well as bowel and bladder function.
· Report senses to your brain - Signals from other parts of your body help your brain record and process sensations like pressure or pain.
· Manage your reflexes - Your spinal cord controls some reflexes (involuntary movements) without involving your brain. For example, your spinal cord manages your patellar reflex (involuntarily moving your leg when someone taps your shin in a certain spot).
So, these signals generated by touch receptors in your skin , they travel along sensory nerves made up of bundled fibers that connect to neurons in the Spinal Cord that move to the Thalamus, which relays information to the rest of the brain. Next stop is the somatosensory cortex, where signals are translated into a touch perception.
However, before we go any further, let's recap what’s “The Thalamus”
Your thalamus is an egg-shaped structure in the middle of your brain. It’s known as a relay station of all incoming motor (movement) and sensory information as hearing, taste, sight and touch (but not smell), from your body to your brain. Like a relay or train station, all information must first pass through your thalamus before being directed to its destination in your brain’s cerebral cortex (the outermost layer of your brain) for further processing and interpretation.
Your thalamus has many functions, including:
· Relaying sensory information - Taking in information, in the form of nerve signals, from all of your senses (taste, touch, hearing, seeing) into your brain. Each sensory function has a thalamic nucleus that receives, processes and transmits the information to its related area within your cerebral cortex.
· Relaying motor (movement) information - Similar to sensory information, motor pathways all pass through your thalamus.
· Prioritizing attention - Your thalamus helps decide what to focus on among the vast amount of information that it receives.
· Role in consciousness - Your thalamus plays a role in keeping you awake and alert.
· Role in thinking (cognition) and memory - Your thalamus is connected with structures of your limbic system, which is involved in processing and regulating emotions, formation and storage of memories, sexual arousal and learning.
Your thalamus also contributes to perception and plays a role in sleep and wakefulness.
Your thalamus work through sensory impulses (“information”) travel through nerve fibers from your body through brain structures to your thalamus. Specialized areas of your thalamus, called nuclei, each area responsible for processing different sensory or motor impulses received from your body and then sending the selected information through nerve fibers to the related area of your cerebral cortex for interpretation (professional, Cleveland Clinic , 2022). For example, information coming through your eye travels to your retina, and then onto your optic nerve. It then travels to The Lateral Geniculate Nucleus(which is one of the areas of the thalamus), which processes the information and sends it to your primary visual cortex for interpretation.
Although it may look like a single structure, you actually have two, side-by-side thalami, one in each hemisphere (side) of your brain. Being located in this central area — like the central hub on a bike wheel — allows nerve fibers connections (like the bike wheel’s spokes) to reach all areas of your cerebral cortex (the outer layer of your brain). Technically, your thalamus is part of an area of your brain called the diencephalon, which includes your hypothalamus, subthalamus and epithalamus(If you want to know more about it, you can to open in other article about anxiety disorders, there I explained a little bit deph about limbic system and hypothalamus).
Your thalamus is a central relay station for receiving incoming sensory and motor information. Your thalamus then sends this information to other parts of your brain. So, damage to your thalamus can affect many functions. Symptoms of damage to your thalamus include:
· Memory loss (amnesia).
· Lack of interest or enthusiasm (apathy).
· Loss of ability to understand language or speak (aphasia).
· Trouble with attention, loss of alertness.
· Trouble processing sensory information.
· Impaired movement.
· Sleepiness.
· Chronic pain.
Damage to your thalamus can result in:
· Unconsciousness and even coma.
· Sleep disorders, such as insomnia and fatal familial insomnia (inability to sleep, leading to death).
· Thalamic aphasia (jumbled words, meaningless speech).
· Movement disorders, including tremors.
· Pain syndromes.
· Vision problems, including vision loss or light sensitivity.
· Thalamic pain syndrome (tingling or burning pain).
We talk so much about information that arrives in the cortex that we forget to say the name of this area and its actual function. The primary somatosensory cortex is located in a ridge of cortex called the postcentral gyrus, which is found in the parietal lobe (Sherman, 2019). The primary somatosensory cortex is responsible for processing somatic sensations.
When these information are sent to the central nervous system are generally divided into four modalities: cutaneous senses (senses of the skin), proprioception (body position), kinesthesis (body movement), and nociception (pain, discomfort). We are going to focus on the cutaneous senses, which respond to tactile, thermal, and pruritic (itchy) stimuli, and events that cause tissue damage. Sensitive areas, like lips and fingertips, stimulate much larger regions of the cortex than less sensitive parts (Olivia Guy-Evans, 2021). A region’s sensitivity depends on the number of receptors per unit area and the distance between them. Unlike the very sensitive lips and hands, receptors on your back are few and far apart so it’s much less sensitive (CHALLENGED, 2022).
Different Receptor Types Are Sensitive to Specific Stimuli
When you Stub your toe on a door jamb too hard, you’ll feel an uncomfortable sensation: pain. Primarily a warning signal, pain is the brain’s way of signaling something is wrong with the body. After your toe encounters the door jamb, special sensory neurons, nociceptors, respond to the impact. Nociceptors are attuned to stimuli that cause tissue damage. They respond to strong stimuli, telling you when something is truly dangerous. Touching the door jamb gently isn’t harmful (Blumenrath, Brain Facts.ORG, 2020). Kick it too hard and you could break a bone. Different nociceptors are sensitive to different painful stimuli, like thermal (heat or cold), mechanical (wounds), and chemical (toxins or venoms).
The skin can convey many sensations, such as the biting cold of a wind, the comfortable pressure of a hand holding yours, or the irritating itch from a woolen scarf. The different types of information activate specific receptors that convert the stimulation of the skin to electrical nerve impulses, a process called Transduction. Which means one mechanisms that convert stimuli into electrical signals that can be transmitted and processed by the nervous system. Physical or chemical stimulation creates action potentials in a receptor cell in the peripheral nervous system, which is then conducted along the Axon (for those who don't know axon is a region of the neuron that transmits messages) to the central nervous system. There are three main groups of receptors in our skin:
· Mechanoreceptors - responding to mechanical stimuli, such as stroking, stretching, or vibration of the skin.
· Thermoreceptors - responding to cold or hot temperatures.
· Chemoreceptors - responding to certain types of chemicals either applied externally or released within the skin (such as histamine from an inflammation).
The experience of pain usually starts with activation of nociceptors, receptors that fire specifically to potentially tissue-damaging stimuli. Most of the nociceptors are subtypes of either chemoreceptors or mechanoreceptors. When tissue is damaged or inflamed, certain chemical substances are released from the cells, and these substances activate the chemosensitive nociceptors. Mechanoreceptive nociceptors have a high threshold for activation, they respond to mechanical stimulation that is so intense it might damage the tissue.
Injury triggers the release of various chemicals at the site of damage, causing inflammation. This inflammatory “soup” prompts nerve impulses that keep you feeling pain, so you’ll protect the injury. A long-lasting injury may lead to nervous system changes that enhance perceived pain, even without pain stimuli. This neuropathic pain is caused by an over-sensitive nervous system rather than an injury. In diabetic neuropathy, prolonged exposure to high blood sugar damages nerves in the hands and feet, sending signals of numbness, tingling, burning, or aching pain (Holland, 2020).
Histamine receptors activate when skin irritation, bug bites, or allergies trigger the release of histamine in the body. Itch receptors have molecular channels in their cell membrane that open when they detect histamine. Scientists have identified other itch-specific receptors that activate when they detect other molecules including, prostaglandins, neuropeptides, and proteases the body releases in response to pain and irritants.
Action Potentials in the Receptor Cells Travel as Nerve Impulses with Different Speeds
When you step on a pin, this activates a host of mechanoreceptors, many of which are nociceptors. You may have noticed that the sensation changes over time. First you feel a sharp stab that propels you to remove your foot, and only then you feel a wave of more aching pain. The sharp stab is signaled via fast-conducting A-fibers. Myelinated A-delta fibers insulate the nerve, so electrons are channeled effectively and travel faster letting you feel immediate, sharp, and easily identifiable pain. The unpleasant ache you feel after the sharp pin stab is unmyelinated C fibers transmit messages more slowly and their nerve endings spread over a large area. They help you feel dull aches difficult to pinpoint. From the spinal cord, signals head to the thalamus, which relays signals to areas of the cerebral cortex transforming messages into conscious experience. Once aware, you can decide to be more careful the next time you approach the door.
If you and your friend both stub the same toe on the same door jamb, you’ll probably experience the pain differently. Pain depends both on the strength of the stimulus and the emotional state and setting in which the injury occurs. When messages arrive in the cortex, the brain can process them differently depending on whether you had a good day or just broke up with your girlfriend (Guro E. Løseth, 2022).
The cortex sends pain messages to the periaqueductal gray matter, which activates pathways that modulate pain. Pathways send messages to networks that release endorphins natural opioids that act like the pain reliever morphine (University, 2021). Adrenaline produced during emotionally stressful situations also serves as a pain reliever (Chiropractic). Releasing these chemicals helps regulate and reduce pain by intercepting signals traveling through the spinal cord and brainstem (NEUROSCIENTIFICALLY, 2022). No single brain area is responsible for pain and itch perception. Emotional and sensory components create a mosaic of activity influencing how we perceive pain.
Affective Aspects of Touch Are Important for Development and Relationships
Touch senses are not just there for discrimination or detection of potentially painful events, as Harlow and Suomi (1970) demonstrated in a series of heartbreaking experiments where baby monkeys were taken from their mothers. The infant monkeys could choose between two artificial surrogate mothers. One “warm” mother without food but with a furry, soft cover; and one “cold”, steel mother with food. The monkey babies spent most of their time clinging to the soft mother, and they went to steel mother to feed, indicating that touch is of “overpowering importance” to the infant (Harlow, 1970). Gentle touch is central for creating and maintaining social relationships in primates. They groom each other by stroking the fur and removing parasites. An activity important not only for their individual well-being but also for group cohesion (Dunbar, 2010). Gentle touch is important for us, too.
The sense of touch is the first to develop while one is in the womb, and human infants crave touch from the moment they’re born. From studies of human orphans, we know that touch is also crucial for human development. In Romanian orphanages where the babies were fed but not given regular attention or physical contact, the children suffered cognitive and neurodevelopmental delay (Simons, 1987).
Physical contact helps a crying baby calm down, and the soothing touch a mother gives to her child is thought to reduce the levels of stress hormones such as cortisol. High levels of cortisol have negative effects on neural development, and they can even lead to cell loss (Feldman, (2010).) (Fleming, 1999) (Pechtel, 2011). Thus, stress reduction through hugs and caresses might be important not only for children’s well-being, but also for the development of the infant brain.
How far can we support the pain?
In the my case, I don’t need a lot of time LOL, my brain is specialized in shut offin these cases that involved pain. But in the Aron’s situation is really amazing. In April 2003, the climber Aron Ralston found himself at the floor of Blue John Canyon in Utah, forced to make an appalling choice: face a slow but certain death or amputate his right arm. He fell down the canyon and lies with his right arm trapped between an 800-lb boulder and the steep sandstone wall. Weak from lack of food and water and close to giving up, it occurred to him like an epiphany that if he broke the two bones in his forearm he could manage to cut off the rest with his pocket knife. The pain was unimportant in these case. Only cutting through the thick white main nerve made him delay for a minute LOL. The flood of pain, he describes, was like thrusting his entire arm “into a cauldron of magma.” Finally free, he rappelled down a cliff and walked another 7 miles until he was rescued by some hikers(Ralston, Aron Ralston's 127 hours: This is going to make one hell of a story. . ., (2010). How is it possible to do something so excruciatingly painful to yourself, and still manage to walk, talk, and think rationally afterwards? The answer lies within the brain, where signals from the body are interpreted.
When we perceive somatosensory and nociceptive signals from the body, the experience is highly subjective and malleable by motivation, attention, emotion, and context.
According to the motivation and decision model, the brain automatically and continuously evaluates the pros and cons of any situation (Fields, 2004). Weighing impending threats and available rewards system. In Aron’s extreme case, his actions were likely based on such an unconscious decision process. Taking into account his homeostatic state (his hunger, thirst, the inflammation and decay of his crushed hand slowly affecting the rest of his body), the sensory input available and his knowledge about the threats facing him (death, or excruciating pain that won’t kill him) versus the potential rewards (survival, seeing his family again). Aron’s story illustrates the evolutionary advantage to being able to shut off pain.
The Analgesic Power of Reward
Social rewards, like holding the hands or just seeing the picture of a loved one, can reduce sensations of pain. Thinking about the good things, like his loved ones and the life ahead of him, was probably pivotal to Aron’s survival. The promise of a reward can be enough to relieve pain. From a medical treatment contributes to the Placebo (Eippert F. F., 2009). However, much remains to be learned about the neural and cognitive mechanisms by which placebo treatments have their effects. Placebo analgesic treatments elicit expectations of pain relief, which are thought to change the affective and motivational context in which nociceptive signals are interpreted. Although ample evidence exists that placebo expectancies reduce reported pain, the neurobiology of how expectancies interact with nociceptive brain processes is relatively unexplored (V De Pascalis, 2002) (J, (1969).) (DD Price, (1999)) (L Vase, (2003).) (NJ Voudouris, (1989).)
Eating tasty food, listening to good music, or feeling pleasant touch on your skin also decreases pain in both animals and humans, presumably through the same mechanism in the brain (Leknes S. &., 2008).
In a now classic experiment, Dum and Herz (Dum, (1984)) either rats was fed with normal food or let them feast on highly rewarding chocolate-covered candy (rats love sweets). while they are on a metal plate waiting for food,the plate was heated up to a noxious/painful level, the rats that expected candy endured the temperature for twice as long as the rats expecting normal chow. Moreover, this effect was completely abolished when the rats’ opioid (endorphin) system was blocked with a drug, indicating that the analgesic effect of reward anticipation was caused by endorphin release.
For Aron the climber, both the stress from knowing that death was impending and the anticipation of the reward it would be to survive probably flooded his brain with endorphins, contributing to the wave of excitement and euphoria he experienced while he carried out the amputation (Ralston, Aron Ralston's 127 hours: This is going to make one hell of a story. . ., 2010).This altered his experience of the pain from the extreme tissue damage he was causing and enabled him to focus on freeing himself.
Our brain, it turns out, can modulate the perception of how unpleasant pain is, while still retaining the ability to experience the intensity of the sensation (Rainville, 1997). Social rewards, like holding the hand of your boyfriend or girlfriend, have pain-reducing effects. Even looking at a picture of him/her can have similar effects. In fact, seeing a picture of a person we feel close to not only reduces subjective pain ratings, but also the activity in pain-related brain areas (Eisenberger, 2011). The most common things to do when wanting to help someone through a painful experience being present and holding the person’s hand, thus seems to have a measurably positive effect.
When Touch Becomes Painful or Pain Becomes Chronic
Chances are you’ve been sunburned a few times in your life and have experienced how even the lightest pat on the back or the softest clothes can feel painful on your over-sensitive skin. This condition, where innocuous touch gives a burning, tender sensation, is similar to a chronic condition called allodynia. It’s pain due to a stimulus that does not normally provoke pain, when a light, stroking touch feels painful. In allodynia, neuronal injury in the spinal dorsal horn causes Aβ-afferents, which are activated by non-nociceptive touch, to access nociceptive pathways (Liljencrantz, 2013). The result is that even gentle touch is interpreted by the brain as painful. While an acute pain response to Noxious Stimuli (a stimulus that is damaging or threatens damage to normal tissues). Has a vital protective function, allodynia and other Chronic Pain conditions constitute a tremendous source of unnecessary suffering that affects millions of people.
The relative meaning of pain is illustrated by a recent experiment, where the same moderately painful heat was administered to participants in two different contexts—one control context where the alternative was a nonpainful heat; and another where the alternative was an intensely painful heat. In the control context, where the moderate heat was the least preferable outcome, it was (unsurprisingly) rated as painful. In the other context it was the best possible outcome, and here the exact same moderately painful heat was actually rated as pleasant because it meant the intensely painful heat had been avoided. This somewhat surprising change in perception, where pain becomes pleasant because it represents relief from something worse, highlights the importance of the meaning individuals ascribe to their pain, which can have decisive effects in pain treatment (Leknes S. B., (2013)). In the case of touch, knowing who or what is stroking your skin can make all the difference—try thinking about slugs the next time someone strokes your skin if you want an illustration of this point. In a recent study, a group of heterosexual males were told that they were about to receive sensual caresses on the leg by either a male experimenter or by an attractive female experimenter (Gazzola, 2012).The study participants could not see who was touching them. Although it was always the female experimenter who performed the caress, the heterosexual males rated the otherwise pleasant sensual caresses as clearly unpleasant when they believed the male experimenter did it.
Pain and pleasure not only share modulatory systems—another common attribute is that we don’t need to be on the receiving end of it ourselves in order to experience it. How did you feel when you read about Aron cutting through his own tissue, or “Thomas” destroying his own bones unknowingly? Did you cringe? It’s quite likely that some of your brain areas processing affective aspects of pain were active even though the nociceptors in your skin and deep tissue were not firing. Pain can be experienced vicariously, as can itch, pleasurable touch, and other sensations.
HOPE I HELPED YOU S2
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