Pain: Definition and Early Discoveries
The International Association for the Study of Pain defines pain as an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage.
In simpler terms, pain is not merely a physical sensation—it also encompasses an emotional dimension of distress or suffering. In fact, neuroscientists have found that the brain regions activated by physical pain overlap with those activated by emotional pain. For example, the pain of social rejection or grief can stimulate the same brain areas involved in physical pain.
The scientific revolution of the 17th century marked a turning point in how pain was understood. A key development in the mid-18th century came from Swiss physician Albrecht von Haller, who demonstrated that nerves alone produce the sensation of pain, and that an organ feels pain only if it is connected to the brain via nerves.
This was a breakthrough, as it established a strong link between pain and the nervous system. By 1800, physicians understood pain as a sensation transmitted by nerves to the brain. Advances in microscopy and physiology further led to the discovery of specialized receptors and nerve fibers responsible for pain.
Around the same period, medicine underwent a radical transformation with the advent of anesthesia and painkillers. Surgeons discovered ether and chloroform, chemists isolated morphine from opium, and aspirin was later invented.
These innovations proved that pain could be relieved—or even eliminated—through medication, a revolutionary idea at the time, driven by the urgent needs of war and increasing demand for surgery. Anesthesia became widely used by the mid-19th century.
The Pain Scale in Clinical Practice
The "pain scale" is one of the essential clinical tools developed by modern medicine to help patients express the intensity of their pain in a way that healthcare teams can interpret effectively. Pain is inherently subjective and cannot be measured by devices or lab tests; instead, it is assessed based on the patient’s self-report.
To standardize pain assessment and track its progression over time, the numerical pain scale was adopted. Patients are asked to rate their pain on a scale from 0 to 10, where "0" means no pain, and "10" represents the worst imaginable pain.
This tool has evolved gradually over the past fifty years, as part of broader efforts to improve the patient-caregiver relationship. Leading figures in pain medicine and palliative care, such as American nurse Margo McCaffery, helped promote the view that “pain is whatever the patient says it is.” This perspective laid the foundation for complementary tools such as the visual analog scale and the facial expression scale, designed for children or patients unable to communicate verbally.
Today, pain assessment tools are an integral part of routine clinical evaluation and are considered the "fifth vital sign," alongside temperature, pulse, blood pressure, and respiration. The use of the pain scale is not merely about recording a number—it reflects a fundamental shift in medical practice: recognizing the patient’s subjective experience and placing their voice at the heart of clinical decision-making.
The Complexity of Pain
Today, in the 21st century, the study of pain is no longer limited to anesthesiologists and neurologists. It now involves psychologists, philosophers, and even sociologists. Conditions such as chronic pain — pain that persists long after an injury or arises without a clear physical cause — are increasingly being recognized as distinct diseases in their own right. Remarkably, after thousands of years of treating pain as merely a symptom of something else, modern medicine is beginning to focus on pain itself as a primary target for treatment.
Healthcare professionals across disciplines — physicians, pharmacists, nurses, and others — have come to understand that pain is the end result of a complex neural process influenced by many factors. These factors alert the body to harm and transmit signals from receptors in the skin, for example, to the spinal cord and then to the brain, resulting in a behavioral response — like pulling one’s hands away from a hot surface.
Many specialists in these fields now recognize that while we can measure neural signals related to pain, the experience of pain is ultimately subjective. Two people can suffer the same injury and produce similar neural responses, yet report vastly different levels of pain due to differences in genetics, psychology, or life experiences.
Modern pain science embraces this personal dimension and no longer sees it as a flaw in the patient. In fact, researchers increasingly rely on the "biopsychosocial model" to understand pain. This model highlights the complexity of pain and acknowledges that it is shaped by biological factors (nerves, inflammation, etc.), psychological factors (attention, mood, beliefs), and social influences.
How Pain Changes the Brain
Scientists have discovered that pain can alter the brain’s chemistry and structure. A striking 2019 study found that individuals suffering from chronic pain had lower levels of the neurotransmitter glutamate in the prefrontal cortex, a change associated with more negative personality traits such as pessimism and fear.
In other words, chronic pain can physically change the brain. It is also widespread—according to some estimates, one in five adults worldwide experiences chronic pain. Indeed, anyone who has endured long-term pain will tell you: it changes you. Chronic pain can affect mood, behavior, and personal relationships.
People often modify their lifestyles in response to pain. They may give up hobbies, avoid social outings, or become more sedentary for fear of exacerbating the pain. These adaptations can gradually erode parts of a person’s character; an adventurous and outgoing individual may become cautious and withdrawn.
Future Treatments for Pain
Current scientific research is moving toward safer, more precise alternatives for treating pain. These include non-opioid analgesics—compounds that target nerve pain receptors without affecting the brain or causing addiction. Gene therapy is also being explored, including the use of CRISPR technology to deactivate genes responsible for hypersensitivity to pain in certain hereditary conditions. In the future, chronic pain might be treated at its genetic root rather than merely being masked by medication.
Additionally, researchers are developing specialized antibodies that block pain signals in specific conditions, such as diabetic neuropathy or cancer-related pain.
One of the most promising and innovative approaches is the use of virtual reality to distract the brain from pain. In several studies, immersing patients in calming virtual environments has been shown to reduce pain by up to 50% during painful procedures. Home-based VR systems are now being tested to manage chronic pain by retraining the brain to ignore pain signals.
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