Chapter 8. General Principles of Sensory Processing, Touch, and Pain
Follow us on Facebook and Twitter, or subscribe to our mailing list, to receive news updates. Learn more.
Daniel Cressey Researchers have called for a common method of killing zebrafish used in laboratories to be abandoned amid growing evidence that it causes unnecessary suffering. The anaesthetic MS-222, which can be added to tanks to cause overdose, seems to distress the fish, two separate studies have shown. The studies’ authors propose that alternative anaesthetics or methods should be used instead. “These two studies — carried out independently — use different methodologies to reach the same conclusion: zebrafish detect and avoid MS-222 in the water,” says Stewart Owen, a senior environmental scientist at AstraZeneca’s Brixham Environmental Laboratory in Brixham, UK, and a co-author of one of the studies. “As this is a clear aversive response, as a humane choice, one would no longer use this agent for routine zebrafish anaesthesia.” The use of zebrafish (Danio rerio) in research has skyrocketed in recent years as scientists have sought alternatives to more controversial animal models, such as mammals. The fish are cheap and easy to keep, and although no firm data on numbers have been collected, millions are known to be housed in laboratories around the world. Nearly all will eventually be killed. MS-222 (ethyl 3-aminobenzoate methanesulphate, also known as TMS) is one of the agents most frequently used to kill the creatures. It is listed as an acceptable method of euthanasia by many institutions, and also by societies such as the American Veterinary Medical Association. But the study by Owen and his co-authors, published last year (G. D. Readman et al. PLoS ONE 8, e73773; 2013), and the second study, published earlier this month by Daniel Weary and his colleagues at the University of British Columbia in Vancouver, Canada (D. Wong et al. PLoS ONE 9, e88030; 2014), show that zebrafish seem to find the chemical distressing. The research should fundamentally change the practice, say the authors of both papers. © 2014 Nature Publishing Group
Keyword: Pain & Touch
Link ID: 19294 - Posted: 02.26.2014
By Michelle Roberts Health editor, BBC News online Doctors have devised a new way to treat amputees with phantom limb pain. Using computer-generated augmented reality, the patient can see and move a virtual arm controlled by their stump. Electric signals from the muscles in the amputated limb "talk" to the computer, allowing real-time movement. Amputee Ture Johanson says his pain has reduced dramatically thanks to the new computer program, which he now uses regularly in his home. He now has periods when he is free of pain and he is no longer woken at night by intense periods of pain. Mr Johanson, who is 73 and lives in Sweden, lost half of his right arm in a car accident 48 years ago. After a below-elbow amputation he faced daily pain and discomfort emanating from his now missing arm and hand. Over the decades he has tried numerous therapies, including hypnosis, to no avail. Within weeks of starting on the augmented reality treatment in Max Ortiz Catalan's clinic at Chalmers University of Technology, his pain has now eased. "The pain is much less now. I still have it often but it is shorter, for only a few seconds where before it was for minutes. BBC © 2014
By DENISE GRADY The experiment was not for the squirmish. Volunteers were made to itch like crazy on one arm, but not allowed to scratch. Then they were whisked into an M.R.I. scanner to see what parts of their brains lit up when they itched, when researchers scratched them and when they were finally allowed to scratch themselves. The scientific question was this: Why does it feel so good to scratch an itch? “It’s quite intriguing to see how many brain centers are activated,” said Dr. Gil Yosipovitch, chairman of dermatology at the Temple University School of Medicine and director of the Temple Center for Itch (he conducted the experiment while working at Wake Forest School of Medicine). “There is no one itch center. Everyone wants that target, but it doesn’t work in real life like that.” Instead, itching and scratching engage brain areas involved not only in sensation, but also in mental processes that help explain why we love to scratch: motivation and reward, pleasure, craving and even addiction. What an itch turns on, a scratch turns off — and scratching oneself does it better than being scratched by someone else. The study results were published in December in the journal PLOS One. Itching was long overshadowed by pain in both research and treatment, and was even considered just a mild form of pain. But millions of people suffer from itching, and times have changed. Research has found nerves, molecules and cellular receptors that are specific for itching and set it apart from pain, and the medical profession has begun to take it seriously as a debilitating problem that deserves to be studied and treated. Within the last decade, there has been a flurry of research into what causes itching and how to stop it. Along with brain imaging, studies have begun to look at gene activity and to map the signals that flow between cells in the skin, the immune system, the spinal cord and the brain. © 2014 The New York Times Company
Keyword: Pain & Touch
Link ID: 19264 - Posted: 02.18.2014
by Bethany Brookshire There are times when science is a painful experience. My most excruciating moment in science involved a heated electrode placed on my bare leg. This wasn’t some sort of graduate school hazing ritual. I was a volunteer in a study to determine how we process feelings of pain. As part of the experiment I was exposed to different levels of heat and asked how painful I thought they were. When the electrode was removed, I eagerly asked how my pain tolerance compared with that of others. I secretly hoped that I was some sort of superwoman, capable of feeling pain that would send other people into screaming fits and brushing it off with a stoic grimace. It turns out, however, that I was a bit of a wuss. Ouch. I figured I could just blame my genes. About half of our susceptibility to pain can be explained by genetic differences. The other half, however, remains up for grabs. And a new study published February 4 in Nature Communications suggests that part of our susceptibility to pain might lie in chemical markers on our genes. These “notes” on your DNA, known as epigenetic changes, can be affected by environment, behavior and even diet. So the findings reveal that our genetic susceptibility to pain might not be our destiny. Tim Spector and Jordana Bell, genetic epidemiologists at King’s College London, were interested in the role of the epigenome in pain sensitivity. Epigenetic changes such as the addition (or subtraction) of a methyl group on a gene make that gene more or less likely to be used in a cell by altering how much protein can be made from it. These differences in proteins can affect everything from obesity to memory to whether you end up like your mother. © Society for Science & the Public 2000 - 2013.
By Veronique Greenwood Young animals are capable of some pretty astounding feats of navigation. To a species like ours, whose native sense of direction isn’t much to speak of—have you ever seen a human baby crawl five thousand miles home?—the intercontinental odysseys some critters make seem incomprehensible. Arctic tern chicks take part in the longest migration on Earth—more than ten thousand miles (16,000 km)—almost as soon as they fledge. Soon after hatching, young sea turtles take to the waves and confidently paddle many thousands of miles to feeding grounds. Young Chinook salmon likewise make their way from freshwater hatching grounds to specific feeding areas in the open ocean. Biologists know that these species are able to sense things that humans can’t, from the Earth’s magnetic field to extremely faint scents, that could help with navigation. But they may also be inheriting some specific knowledge of the paths they have to follow. A paper in this week’s Current Biology reports that young salmon appear to possess an inborn map of the geomagnetic field that can help them get where they need to go. The researchers, who are primarily based at Oregon State University, performed a series of experiments with Chinook salmon less than a year old that were born and raised in a hatchery and had not yet taken part in a migration. They placed the salmon in pools surrounded by magnetic coils that they could tune to mimic the Earth’s magnetic field at various points in and around the salmons’ feeding grounds. (Kenneth Lohmann at University of North Carolina, Chapel Hill, who has done similar studies that established that baby sea turtles have inborn maps, is also an author of the paper.) © 2014 Time Inc.
Keyword: Animal Migration
Link ID: 19220 - Posted: 02.08.2014
by Douglas Heaven We have the world at our fingertips. A sense of touch can sometimes be as important as sight, helping us to avoid crushing delicate objects or ensuring that we hold on firmly when carrying hot cups of coffee. Now, for the first time, a person who lost his left hand has had a near-natural sense of touch restored thanks to a prosthesis. "I didn't realise it was possible," says Dennis Aabo Sørensen, who is so far the only person to have been fitted with the new prosthesis. "The feeling is very close to the sensation you get when you touch things with your normal hand." To restore Sørensen's sense of touch, Silvestro Micera at the Swiss Federal Institute of Technology in Lausanne and his colleagues implanted tiny electrodes inside the ulnar and median nerve bundles in Sørensen's upper arm. Between them, the ulnar nerve – which runs down to the little finger and ring finger – and the median nerve – which runs down to the index and middle fingers – carry sensations from most of the hand, including the palm. The team then connected the electrodes to pressure sensors on the fingertips and palm of a robotic prosthetic hand via cables running down the outside of Sørensen's arm. When he used the hand to grasp an object, electrical signals from the pressure pads were fired directly into the nerves, providing him with a sense of touch. Getting to grips The electrical signals were calibrated so that Sørensen could feel a range of sensation, from the slightest touch to firm pressure just below his pain threshold, depending on the strength of his grip. © Copyright Reed Business Information Ltd.
by Andy Coghlan If you flinch where others merely frown, you might want to take a look at your lifestyle. That's because environmental factors may have retuned your genes to make you more sensitive to pain. "We know that stressful life events such as diet, smoking, drinking and exposure to pollution all have effects on your genes, but we didn't know if they specifically affected pain genes," says Tim Spector of King's College London. Now, a study of identical twins suggests they do. It seems that epigenetic changes – environmentally triggered chemical alterations that affect how active your genes are – can dial your pain threshold up or down. This implies that genetic tweaks of this kind, such as the addition of one or more methyl groups to a gene, may account for some differences in how our senses operate. Spector and his colleagues assessed the ability of hundreds of pairs of twins to withstand the heat of a laser on their skin, a standard pain test. They selected 25 pairs who showed the greatest difference in the highest temperature they could bear. Since identical twins have the same genes, any variation in pain sensitivity can be attributed to epigenetic differences. Pain thermostat The researchers screened the twins' DNA for differences in methylation levels across 10 million gene regions. They found a significant difference in nine genes, most of which then turned out to have been previously implicated in pain-sensitivity in animal experiments. © Copyright Reed Business Information Ltd.
by Kat Arney Next time you struggle to resist an itchy rash or insect bite, you could find relief in the mirror. Perception of our own bodies can be easily manipulated using tricks such as the rubber hand illusion, which fools people into thinking a rubber hand is their own. Reflecting someone's limb in a mirror has also been used to treat phantom limb pain. Now Christoph Helmchen and his colleagues at the University of Lübeck in Germany have shown that a similar mirror illusion can fool people into feeling relief from an itch, even when they scratch the wrong place. The team injected the right forearms of 26 male volunteers with itch-inducing chemical histamine. Because the injection creates a red spot, they painted a corresponding dot on the opposite arm so both looked identical. One of the researchers then scratched each arm in turn. Unsurprisingly, scratching the itchy arm produced relief, while scratching the other one did not. Next, they placed a large vertical mirror in front of the itchy arm, blocking off the subject's view of their right arm and reflecting back the non-itchy one in its place . They asked the volunteers to look only at the reflected limb in the mirror, whilst a member of the team again scratched each arm. This time the participants felt relief when the unaffected, reflected arm was scratched. © Copyright Reed Business Information Ltd.
By Roni Jacobson Over the past 10 years the number of overdose deaths from prescription painkillers—also known as opioid analgesics—has tripled, from 4,000 people in 1999 to more than 15,000 people every year in the U.S. today. Prescription pain medication now causes more overdose deaths than heroin and cocaine combined. In 2010 one in 20 Americans older than age 12 reported taking painkillers recreationally; some steal from pharmacies or buy them from a dealer, but most have a doctor's prescription or gain access to pills through friends and relatives. Yet millions of people legitimately rely on these medications to cope with the crippling pain they face every day. How do we make sure prescription opioids are readily available to those who depend on them for medical relief but not so available that they become easily abused? Here we break down the steps taken at various levels—and the experts' recommendations for future interventions—to curb prescription opioid addiction and overdose in the U.S. © 2014 Scientific American
By Michelle Roberts Health editor, BBC News online A magnet device can be used to treat some types of migraine, new UK guidance advises. The watchdog NICE says although there is limited evidence, transcranial magnetic stimulation (TMS) may help ease symptoms in some patients. It says that the procedure is still relatively new and that more data is needed about its long-term safety and efficacy. But it may be useful for patients for whom other treatments have failed. Migraine is common - it affects about one in four women and one in 12 men in the UK. There are several types - with and without aura and with or without headache - and several treatment options, including common painkillers, such as paracetamol. Although there is no cure for migraine, it is often possible to prevent or lessen the severity of attacks. NICE recommends various medications, as well as acupuncture, and now also TMS, under the supervision of a specialist doctor - although it has not assessed whether it would be a cost effective therapy for the NHS. TMS involves using a portable device that is placed on the scalp to deliver a brief magnetic pulse. NICE says doctors and patients might wish to try TMS, but they should be aware about the treatment's uncertainties. Reduction in migraine symptoms may be moderate, it says. Prof Peter Goadsby, chairman of the British Association for the Study of Headache, said many migraine patients stood to benefit from trying TMS. BBC © 2014
Keyword: Pain & Touch
Link ID: 19158 - Posted: 01.22.2014
Things are heating up in the world of genetics. The hot pepper (Capsicum annuum) is one of the most widely grown spice crops globally, playing an important role in many medicines, makeups, and meals worldwide. Although the plant’s so-called capsaicin chemical is well known for spicing things up, until now the genetic spark responsible for the pepper’s pungency was unknown. A team of scientists recently completed the first high-quality reference genome for the hot pepper. Comparing the pepper’s genome with that of its tame cousin, the tomato, the scientists discovered the gene responsible for fiery capsaicin production appeared in both plants. While the tomato carried four nonfunctioning copies of the gene, the hot pepper carried seven nonfunctioning copies and one functioning copy, the team reports online today in Nature Genetics. The researchers believe the pepper’s capsaicin-creating gene appeared after five mutations occurred during DNA replication, with the final mutation creating a functional copy. The mouth-burning chemicals likely protected the mutant pepper’s seeds from grazing land animals millions of years ago, giving the mutant a reproductive advantage and helping the mutant gene spread. The team says the finding could help breeders boost the pepper’s heat, nutrition, and medicinal properties. One researcher even suggests that geneticists could activate one of the tomato’s dormant genes, enabling capsaicinoid production and creating a plant that makes ready-made salsa. © 2014 American Association for the Advancement of Science.
-- Bats and other animals use ultrasound to their advantage. Now a new study of humans suggests ultrasound can alter brain activity to boost people's sensory perception. First, researchers placed an electrode on the wrist of volunteers to stimulate the nerve that runs down the arm and into the hand. Before stimulating the radial nerve, they delivered ultrasound to the head -- to an area of the cerebral cortex that processes sensory information received from the hand. The participants' brain responses were recorded using electroencephalography (EEG). The ultrasound decreased the EEG signal and weakened the brain waves responsible for processing sensory input from the hands, according to the study published online Jan. 12 in the journal Nature Neuroscience. The Virginia Tech researchers then conducted two common neurological tests. One measures a person's ability to distinguish whether two pins placed close together and touching the skin are actually two distinct contact points. The other test measures sensitivity to the frequency of a series of air puffs. The scientists were surprised to discover that when they received ultrasound, the participants showed significant improvements in their ability to distinguish pins at closer distances and to identify small differences in the frequency of successive air puffs. The ultrasound may have changed the balance of inhibition and excitation between neighboring neurons within the cerebral cortex, resulting in a boost in sensory perception, explained study leader William Tyler, an assistant professor at Virginia Tech's Carilion Research Institute. © 2014 HealthDay
Keyword: Pain & Touch
Link ID: 19147 - Posted: 01.18.2014
By NICHOLAS BAKALAR Both acupuncture and sham acupuncture were effective in reducing menopausal symptoms in women being treated with aromatase inhibitors for breast cancer, a small randomized trial found. Joint and muscle pain, hot flashes and night sweats are common side effects of those estrogen-lowering drugs. The trial, published online in Cancer, randomized 47 breast cancer patients to eight weekly sessions of either real or sham acupuncture. Those assigned to real acupuncture received treatment with needles in recognized acupoints believed to be helpful in relieving menopausal symptoms. The controls got non-penetrating needles placed in sham acupuncture points. Patients and researchers did not know which patients had received which treatment. The patients kept daily diaries or filled out several questionnaires on the frequency and severity of hot flashes and other symptoms. Patient-reported symptoms, especially hot flashes, improved significantly after both sham and real treatment. There was no statistically significant difference between the two groups. The results may be attributable to a placebo effect, but the scientists suggest that the slight pricking of the skin could cause physiological changes. In any case, the lead author, Dr. Ting Bao, a medical oncologist at the University of Maryland, Baltimore, said there is no harm in trying acupuncture. “Acupuncture as a medical procedure has been practiced for thousands of years,” she said. “It has a minimal risk and potentially significant benefits.” Copyright 2013 The New York Times Company
Keyword: Pain & Touch
Link ID: 19074 - Posted: 12.28.2013
By Dana Smith Daniel Tammet has memorized Pi to the 22,514th digit. He speaks ten different languages, including one of his own invention, and he can multiply enormous sums in his head within a matter of seconds. However, he is unable to hold down a standard 9-to-5 job, in part due to his obsessive adherence to ritual, down to the precise times he has his tea every day. Daniel is a savant. He is also autistic. And he is a synesthete. Daniel experiences numbers as having color, as well as shape and texture. This helps him perform amazing mathematical feats seemingly without effort, the answer simply materializing to him rather than having to calculate it out. In an interview he gave with The Guardian, Daniel explained, “When I multiply numbers together, I see two shapes. The image starts to change and evolve, and a third shape emerges. That’s the answer. It’s mental imagery. It’s like maths without having to think.” Clearly this man has an extraordinary brain. However, Daniel is perhaps not entirely unique, and it appears that the link between autism and synesthesia is more common than originally thought. This suggests that there is a potential common mechanism between these two conditions, which may even help to explain some of Daniel’s special savant abilities. A new study published in the journal Molecular Autism from a team of researchers at the University of Cambridge now empirically shows that there is an almost three-fold higher occurrence of synesthesia in individuals with autism (18.9%), compared with that of the general population (7.2%). This increased prevalence implies that there is indeed a significant link between autism and synesthesia. © 2013 Scientific American
Link ID: 19008 - Posted: 12.06.2013
By RONI CARYN RABIN Women are more likely than men to die after a heart attack, and some researchers have suggested a reason: Doctors may be misdiagnosing women more often because their symptoms differ from those experienced by men. But a study published Monday indicates that too much has been made of gender differences in chest pain, the hallmark symptom of heart disease. Although the researchers found some distinctions, no pattern was clearly more characteristic of women or could be used to improve heart attack diagnosis in women, the authors concluded. “We should stop treating women differently at the emergency room when they present with chest pain and discomfort,” said Dr. Maria Rubini Gimenez, a cardiologist at University Hospital Basel and lead author of the new study, published in JAMA Internal Medicine. Instead, she said, all patients with acute chest pain must be evaluated for heart attack with appropriate diagnostics, including an electrocardiogram and blood tests. Roughly 80 percent of people who have chest pain and discomfort are suffering from indigestion, acid reflux or another relatively benign condition, said Dr. John G. Canto, director of the chest pain center at Lakeland Regional Medical Center in Lakeland, Fla., who has researched heart attack diagnosis. “The trick is, how do you figure out the 15 to 20 percent actually having a heart attack?” he said. The new research confirms “that there is a lot of overlap in symptoms between patients who are having a heart attack and those who aren’t, and there is a lot of overlap in symptoms between men and women.” The new study examined 2,475 patients, including 796 women, who reported to emergency rooms at nine hospitals in Switzerland, Spain and Italy complaining of acute chest pain between April 21, 2006, and Aug. 12, 2012. Copyright 2013 The New York Times Company
by Erika Engelhaupt If you had to have a prosthetic hand, would you want it to look like a real hand? Or would you prefer a gleaming metallic number, something that doesn’t even try to look human? A new study looks at one of the issues that prosthetic designers and wearers face in making this decision: the creepy factor. People tend to get creeped out by robots or prosthetic devices that look almost, but not quite, human. So Ellen Poliakoff and colleagues at the University of Manchester in England had people rate the eeriness of various prosthetic hands. Forty-three volunteers looked at photographs of prosthetic and real hands. They rated both how humanlike (realistic) the hands were and how eerie they were, defined as “mysterious, strange, or unexpected as to send a chill up the spine.” Real human hands were rated both the most humanlike and the least eerie (a good thing for humans). Metal hands that were clearly mechanical were rated the least humanlike, but less eerie overall than prosthetic hands made to look like real hands, the team reports in the latest issue of Perception. The realistic prosthetics, like the rubber hand shown above, fell into what's known as the uncanny valley. That term, invented by roboticist Matsuhiro Mori in 1970, describes how robots become unnerving as they come to look more humanlike. The superrealistic Geminoid DK robot and the animated characters in the movie The Polar Express suffer from this problem. They look almost human, but not quite, and this mismatch between expectation and reality is one of the proposed explanations for the uncanny valley. In particular, if something looks like a human but doesn’t quite move like one, it’s often considered eerie. © Society for Science & the Public 2000 - 2013
by Simon Makin "The only thing we have to fear is fear itself," said Franklin D. Roosevelt. He might have been onto something: research suggests that the anticipation of pain is actually worse than the pain itself. In other words, people are happy to endure a bit more pain, if it means they spend less time waiting for it. Classical theories of decision-making suppose that people bring rewards forward and postpone punishments, because we give far-off events less weight. This is called "temporal discounting". But this theory seems to go out the window when it comes to pain. One explanation for this is that the anticipation of pain is itself unpleasant, a phenomenon that researchers have appropriately termed "dread". To investigate how dread varies with time, Giles Story at University College London, and his colleagues, hooked up 33 volunteers to a device that gave them mild electric shocks. The researchers also presented people with a series of choices between more or less mildly painful shocks, sooner or later. During every "episode" there was a minimum of two shocks, which could rise to a maximum of 14, but before they were given them, people had to make a choice such as nine extra shocks now or six extra shocks five episodes from now. The number of shocks they received each time was determined by these past choices. Although a few people always chose to experience the minimum pain, 70 per cent of the time, on average, participants chose to receive the extra shocks sooner rather than a smaller number later. By varying the number of shocks and when they occurred, the team was able to figure out that the dread of pain increased exponentially as pain approached in time. Similar results occurred in a test using hypothetical dental appointments. © Copyright Reed Business Information Ltd.
By Helen Briggs BBC News A condition where people experience a mixing of the senses, such as tasting words, has been linked with autism. Research suggests synaesthesia is nearly three times as common in adults with autism spectrum disorder than in the general population. The two conditions may share common features such as unusual wiring of the brain, say UK scientists. The study helps understanding of how people with autism experience life, says the National Autistic Society. Synaesthesia is a condition where one sense automatically triggers another. Some people experience tastes when they read or hear words, some perceive numbers as shapes, others see colours when they hear music. People with synaesthesia might say: "The letter q is dark brown," or: "The word 'hello' tastes like coffee," for example. Following anecdotal evidence of links between synaesthesia and Asperger's syndrome, researchers at the Autism Research Centre at Cambridge University set out to test the idea. More than 200 study participants - 164 adults diagnosed with high-functioning autism or Asperger's syndrome, and 97 adults without autism - were asked to fill in questionnaires to measure synaesthesia and autism traits. The study found one in five adults with autism spectrum conditions - a range of related developmental disorders, including autism and Asperger's syndrome - had synaesthesia compared with about 7% of people with no signs of the disorders. Prof Simon Baron-Cohen, who led the research, told BBC News: "Synaesthesia involves a mixing of the senses and it's a very subjective private experience, so the only way we know it's happening is if you ask people to report on their experiences. BBC © 2013
Link ID: 18948 - Posted: 11.20.2013
By BARRY MEIER Addiction experts protested loudly when the Food and Drug Administration approved a powerful new opioid painkiller last month, saying that it would set off a wave of abuse much as OxyContin did when it first appeared. An F.D.A. panel had earlier voted, 11 to 2, against approval of the drug, Zohydro, in part because unlike current versions of OxyContin, it is not made in a formulation designed to deter abuse. Now a new issue is being raised about Zohydro. The drug will be manufactured by the same company, Alkermes, that makes a popular medication called Vivitrol, used to treat patients addicted to painkillers or alcohol. In addition, the company provides financial support to a leading professional group that represents substance abuse experts, the American Society of Addiction Medicine. For some critics, the company’s multiple roles in the world of painkillers is troubling. Dr. Gregory L. Jones, an addiction specialist in Louisville, Ky., said he had long been concerned about financial links between the group and the drug industry, adding that the Zohydro situation amplified those potential conflicts. Dr. Stuart Gitlow, the current president of the American Society of Addiction Medicine, said he had been unaware until now of Alkermes’s involvement with Zohydro. Dr. Gitlow, who is affiliated with Mount Sinai Hospital in New York City, said that the group would seek more information from Alkermes about the situation and then decide what, if anything, to do next. Officials of Alkermes appear to recognize the issue they face. In recent years, the company has been trying to increase sales of Vivitrol, a form of a drug called naltrexone, that is used to treat both alcoholism and opioid addiction. © 2013 The New York Times Company
By JANE E. BRODY Marijuana has been used medically, recreationally and spiritually for about 5,000 years. Known botanically as cannabis, it has been called a “crude drug”: marijuana contains more than 400 chemicals from 18 chemical families. More than 2,000 compounds are released when it is smoked, and as with tobacco, there are dangers in smoking it. Medical marijuana clinics operate in 20 states and the District of Columbia, and its recreational use is now legal in Colorado and Washington. A Gallup poll conducted last month found that 58 percent of Americans support the legalization of marijuana. Yet researchers have been able to do relatively little to test its most promising ingredients for biological activity, safety and side effects. The main reason is marijuana’s classification by Congress in 1970 as an illegal Schedule I drug, defined as having a potential for abuse and addiction and no medical value. American scientists seeking clarification of marijuana’s medical usefulness have long been stymied by this draconian classification, usually reserved for street drugs like heroin with a high potential for abuse. Dr. J. Michael Bostwick, a psychiatrist at the Mayo Clinic in Rochester, Minn., said the classification was primarily political and ignored more than 40 years of scientific research, which has shown that cellular receptors for marijuana’s active ingredients are present throughout the body. Natural substances called cannabinoids bind to them to influence a wide range of body processes. In a lengthy report entitled “Blurred Boundaries: The Therapeutics and Politics of Medical Marijuana,” published last year in Mayo Clinic Proceedings, Dr. Bostwick noted that the so-called endocannabinoid system has an impact on the “autonomic nervous system, immune system, gastrointestinal tract, reproductive system, cardiovascular system and endocrine network.” Copyright 2013 The New York Times Company