Pain in animals
Encyclopedia
International Association for the Study of Pain
The International Association for the Study of Pain is an international professional organization promoting research, education and policies for the knowledge and management of pain. The IASP was founded in 1973, following the Seattle-Issaquah conference, under the leadership of John Bonica. Its...
says pain is a conscious experience involving unpleasantness, i.e. suffering
Suffering
Suffering, or pain in a broad sense, is an individual's basic affective experience of unpleasantness and aversion associated with harm or threat of harm. Suffering may be qualified as physical or mental. It may come in all degrees of intensity, from mild to intolerable. Factors of duration and...
. For a creature to experience pain, by that definition, it must be capable of consciousness
Consciousness
Consciousness is a term that refers to the relationship between the mind and the world with which it interacts. It has been defined as: subjectivity, awareness, the ability to experience or to feel, wakefulness, having a sense of selfhood, and the executive control system of the mind...
and suffering.
The standard measure of pain in a human is that person's testimony, because only they can know the pain's quality and intensity, and the degree of suffering. Animals without human language cannot report their feelings, and whether they are conscious and capable of suffering has been a matter of some debate.
All vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
s and some invertebrates are capable of nociception
Nociception
Nociception is defined as "the neural processes of encoding and processing noxious stimuli." It is the afferent activity produced in the peripheral and central nervous system by stimuli that have the potential to damage tissue...
, a neural
Nervous system
The nervous system is an organ system containing a network of specialized cells called neurons that coordinate the actions of an animal and transmit signals between different parts of its body. In most animals the nervous system consists of two parts, central and peripheral. The central nervous...
response to intense or damaging stimuli. Nociception can be observed using modern imaging techniques, and a physiological and behavioral response to nociception can be detected but, presently, there is no objective measure of suffering.
History
The idea that animals might not experience painPain
Pain is an unpleasant sensation often caused by intense or damaging stimuli such as stubbing a toe, burning a finger, putting iodine on a cut, and bumping the "funny bone."...
or suffering
Suffering
Suffering, or pain in a broad sense, is an individual's basic affective experience of unpleasantness and aversion associated with harm or threat of harm. Suffering may be qualified as physical or mental. It may come in all degrees of intensity, from mild to intolerable. Factors of duration and...
as humans do traces back at least to the 17th-century French philosopher, René Descartes
René Descartes
René Descartes ; was a French philosopher and writer who spent most of his adult life in the Dutch Republic. He has been dubbed the 'Father of Modern Philosophy', and much subsequent Western philosophy is a response to his writings, which are studied closely to this day...
, who argued that animals lack consciousness
Consciousness
Consciousness is a term that refers to the relationship between the mind and the world with which it interacts. It has been defined as: subjectivity, awareness, the ability to experience or to feel, wakefulness, having a sense of selfhood, and the executive control system of the mind...
.Researchers remained unsure into the 1980s as to whether animals experience pain, and veterinarians trained in the U.S. before 1989 were simply taught to ignore animal pain. In his interactions with scientists and other veterinarians, Bernard Rollin
Bernard Rollin
Bernard E. Rollin is an American philosopher who specializes in animal rights and animal consciousness. He is a professor of philosophy, animal sciences, and biomedical sciences at Colorado State University....
was regularly asked to "prove" that animals are conscious, and to provide "scientifically acceptable" grounds for claiming that they feel pain. Some authors say that the view that animals feel pain differently is now a minority view. Academic reviews of the topic are more equivocal, noting that, although it is likely that some animals have at least simple conscious thoughts and feelings, some authors continue to question how reliably animal mental states can be determined.
In different species
The ability to experience pain in an animal, or another human for that matter, cannot be determined directly but it may be inferred through physiological and behavioral reactions.Some criteria that may indicate the potential to feel pain include:
- Has a suitable nervous systemNervous systemThe nervous system is an organ system containing a network of specialized cells called neurons that coordinate the actions of an animal and transmit signals between different parts of its body. In most animals the nervous system consists of two parts, central and peripheral. The central nervous...
and receptorsSensory receptorIn a sensory system, a sensory receptor is a sensory nerve ending that responds to a stimulus in the internal or external environment of an organism... - Physiological changes to noxious stimuli
- Displays protective motor reactions that might include reduced use of an affected area such as limping, rubbing, holding or autotomyAutotomyAutotomy or self amputation is the act whereby an animal severs one or more of its own appendages, usually as a self-defense mechanism designed to elude a predator's grasp...
- Has opioid receptorOpioid receptorOpioid receptors are a group of G protein-coupled receptors with opioids as ligands. The endogenous opioids are dynorphins, enkephalins, endorphins, endomorphins and nociceptin. The opioid receptors are ~40% identical to somatostatin receptors...
s and shows reduced responses to noxious stimuli when given analgesicAnalgesicAn analgesic is any member of the group of drugs used to relieve pain . The word analgesic derives from Greek an- and algos ....
s and local anaesthetics - Shows trade-offs between stimulus avoidance and other motivational requirements
- Shows avoidance learning
- High cognitive ability and sentienceSentienceSentience is the ability to feel, perceive or be conscious, or to have subjective experiences. Eighteenth century philosophers used the concept to distinguish the ability to think from the ability to feel . In modern western philosophy, sentience is the ability to have sensations or experiences...
Fish
Animal protection advocates have raised concerns about the possible suffering of fish caused by angling. In light of recent research, some countries, like Germany, have banned specific types of fishing, and the British RSPCA now formally prosecutes individuals who are cruel to fish.Invertebrates
Though it has been argued that most invertebrates do not feel pain, there is some evidence that invertebrates, especially the decapod crustaceanCrustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s (e.g. crabs and lobsters) and cephalopod
Cephalopod
A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...
s (e.g. octopuses), exhibit behavioural and physiological reactions indicating they may have the capacity for this experience.
Nociceptor
Nociceptor
A nociceptor is a sensory receptor that responds to potentially damaging stimuli by sending nerve signals to the spinal cord and brain. This process, called nociception, usually causes the perception of pain.-History:...
s have been found in nematodes, annelids and molluscs. Most insects do not possess nociceptors, one known exception being the fruit fly
Drosophila melanogaster
Drosophila melanogaster is a species of Diptera, or the order of flies, in the family Drosophilidae. The species is known generally as the common fruit fly or vinegar fly. Starting from Charles W...
. In vertebrates, endogenous opioid
Opioid
An opioid is a psychoactive chemical that works by binding to opioid receptors, which are found principally in the central and peripheral nervous system and the gastrointestinal tract...
s are neurochemicals that moderate pain by interacting with opiate receptors. Opioid peptides and opiate receptors occur naturally in nematodes, molluscs, insects and crustaceans. The presence of opioids in crustaceans has been interpreted as an indication that lobsters may be able to experience pain, although it has been claimed "at present no certain conclusion can be drawn".
One suggested reason for rejecting a pain experience in invertebrates is that invertebrate brains are too small. However, brain size does not necessarily equate to complexity of function. Moreover, weight for body-weight, the cephalopod
Cephalopod
A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...
brain is in the same size bracket as the vertebrate brain, smaller than that of birds and mammals, but as big or bigger than most fish brains.
Crustaceans
The question of whether or not crustaceanCrustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s can experience pain is unresolved. One paper holds that lobsters' opioids may "mediate pain in the same way" as in vertebrates.
Veterinary medicine
Veterinary medicineVeterinary medicine
Veterinary Medicine is the branch of science that deals with the prevention, diagnosis and treatment of disease, disorder and injury in non-human animals...
uses, for actual or potential animal pain, the same analgesic
Analgesic
An analgesic is any member of the group of drugs used to relieve pain . The word analgesic derives from Greek an- and algos ....
s and anesthetics as used in humans.
Dolorimetry
DolorimetryDolorimeter
A dolorimeter is an instrument used to measure pain threshold and pain tolerance. Dolorimetry has been defined as "the measurement of pain sensitivity or pain intensity." There are several kinds of dolorimeter that have been developed...
(dolor: Latin: pain, grief) is the measurement of the pain response in animals, including humans. It is practiced occasionally in medicine, as a diagnostic tool, and is regularly used in research into the basic science of pain, and in testing the efficacy of analgesics. Non-human animal pain measurement techniques include the paw pressure test
Randall-Selitto test
The Randall-Selitto test or paw pressure test is a technique for the measurement of the pain response in animals. It is used in basic pain research and to test the effectiveness of analgetics by observing the reaction to gradually increasing pressure on an inflamed paw...
, tail flick test
Tail flick test
The tail flick test is a test of the pain response in animals. It is used in basic pain research and to measure the effectiveness of analgesics, by observing the reaction to intense heat. It was first described by D'Amour and Smith in 1941....
and hot plate test
Hot plate test
The hot plate test is a test of the pain response in animals. It is used in basic pain research and in testing the effectiveness of analgesics by observing the reaction to pain caused by heat. It was proposed by Eddy and Leimbach in 1953....
.
Laboratory animals
Animals are kept in laboratories for a wide range of reasons, some of which may involve pain, suffering or distress, whilst others (e.g. many of those involved in breeding) will not. The extent to which animal testingAnimal testing
Animal testing, also known as animal experimentation, animal research, and in vivo testing, is the use of non-human animals in experiments. Worldwide it is estimated that the number of vertebrate animals—from zebrafish to non-human primates—ranges from the tens of millions to more than 100 million...
causes pain and suffering in laboratory animals is the subject of much debate. Marian Stamp Dawkins
Marian Stamp Dawkins
Marian Ellina Stamp Dawkins is professor for animal behaviour at the University of Oxford, where she heads the Animal Behaviour Research Group. She has published several books, one of which has been translated into German, and many peer-reviewed papers. She is considered an expert in animal welfare...
defines "suffering" in laboratory animals as the experience of one of "a wide range of extremely unpleasant subjective (mental) states." The United States Department of Agriculture
United States Department of Agriculture
The United States Department of Agriculture is the United States federal executive department responsible for developing and executing U.S. federal government policy on farming, agriculture, and food...
defines a "painful procedure" in an animal study as one that would "reasonably be expected to cause more than slight or momentary pain or distress in a human being to which that procedure was applied." Some critics argue that, paradoxically, researchers raised in the era of increased awareness of animal welfare
Animal welfare
Animal welfare is the physical and psychological well-being of animals.The term animal welfare can also mean human concern for animal welfare or a position in a debate on animal ethics and animal rights...
may be inclined to deny that animals are in pain simply because they do not want to see themselves as people who inflict it. Animal research with the potential to cause pain is regulated by the Animal Welfare Act of 1966 in the US, and research likely to cause "pain, suffering, distress or lasting harm" is regulated by the Animals (Scientific Procedures) Act 1986
Animals (Scientific Procedures) Act 1986
The Animals Act 1986 is an Act of the Parliament of the United Kingdom passed in 1986, which regulates the use of laboratory animals in the UK. The Act permits experiments to be carried out on animals, including procedures involving vivisection, if certain criteria are met...
in the UK.
Severity scales
To date (2011), eleven countries have national severity classification systems relating to pain and suffering experienced by animals used in research: Australia, Canada, Finland, Germany, The Republic of Ireland, The Netherlands, New Zealand, Poland, Sweden, Switzerland, and the UK. The US also has a mandated national scientific animal-use classification system, but it is markedly different from other countries in that it reports on whether pain-relieving drugs were required and/or used. The first severity scales were implemented in 1986 by Finland and the UK. The number of severity categories ranges between 3 (Sweden and Finland) and 9 (Australia). In the UK, research projects are classified as "mild", "moderate", and "substantial" in terms of the suffering the researchers conducting the study say they may cause; a fourth category of "unclassified" means the animal was anesthetized and killed without recovering consciousness. It should be remembered that in the UK system, many research projects (e.g. transgenic breeding, feeding distasteful food) will require a license under the Animals (Scientific Procedures) Act 1986Animals (Scientific Procedures) Act 1986
The Animals Act 1986 is an Act of the Parliament of the United Kingdom passed in 1986, which regulates the use of laboratory animals in the UK. The Act permits experiments to be carried out on animals, including procedures involving vivisection, if certain criteria are met...
, but may cause little or no pain or suffering. In December 2001, 39 percent (1,296) of project licenses in force were classified as "mild", 55 percent (1,811) as "moderate", two percent (63) as "substantial", and 4 percent (139) as "unclassified". In 2009, of the project licenses issued, 35 percent (187) were classified as "mild", 61 percent (330) as "moderate", 2 percent (13) as "severe" and 2 percent (11) as unclassified.
In the US, the Guide for the Care and Use of Laboratory Animals defines the parameters for animal testing regulations. It states, "The ability to experience and respond to pain is widespread in the animal kingdom...Pain is a stressor and, if not relieved, can lead to unacceptable levels of stress and distress in animals." The Guide states that the ability to recognize the symptoms of pain in different species is essential for the people caring for and using animals. Accordingly, all issues of animal pain and distress, and their potential treatment with analgesia and anesthesia, are required regulatory issues for animal protocol approval
Institutional Animal Care and Use Committee
Institutional Animal Care and Use Committees are of central importance to the application of laws to animal research in the United States. Most research involving laboratory animals is funded by the United States National Institutes of Health or other federal agencies...
.
See also
- Animal ethicsAnimal ethicsAnimal ethics can refer to:*Abolitionism *Animal law*Animal rights*Animal welfare*Intrinsic value *Wildlife managementSee also*Animal rights movement*Animal testing*Animal testing regulations*Cruelty to animals...
- Animal cognitionAnimal cognitionAnimal cognition is the title given to the study of the mental capacities of non-human animals. It has developed out of comparative psychology, but has also been strongly influenced by the approach of ethology, behavioral ecology, and evolutionary psychology...
- Bridge locusBridge locusIn neuroscience the bridge locus for a particular sensory percept is a hypothetical set of neurons whose activity is the basis of that sensory percept. The term was introduced by D.N. Teller and E.Y. Pugh, Jr. in 1983, and has been sparingly used...
- Cruelty to animalsCruelty to animalsCruelty to animals, also called animal abuse or animal neglect, is the infliction of suffering or harm upon non-human animals, for purposes other than self-defense. More narrowly, it can be harm for specific gain, such as killing animals for food or for their fur, although opinions differ with...
- Emotion in animalsEmotion in animalsThere is no scientific consensus on emotion in animals, that is, what emotions certain species of animals, including humans, feel. The debate concerns primarily mammals and birds, although emotions have also been postulated for other vertebrates and even for some invertebrates.Animal lovers,...
- Moral status of animals in the ancient worldMoral status of animals in the ancient worldThe 21st-century debates about animal welfare and animal rights can be traced back to the ancient world. The idea that the use of animals by humans—for food, clothing, entertainment, and as research subjects—is morally acceptable, springs mainly from two sources.First, there is the idea...
- Neural correlates of consciousnessNeural correlates of consciousnessThe neural correlates of consciousness constitute the minimal set of neuronal events and mechanisms sufficient for a specific conscious percept. Neuroscientists use empirical approaches to discover neural correlates of subjective phenomena...
- Philosophy of mindPhilosophy of mindPhilosophy of mind is a branch of philosophy that studies the nature of the mind, mental events, mental functions, mental properties, consciousness and their relationship to the physical body, particularly the brain. The mind-body problem, i.e...
- SentienceSentienceSentience is the ability to feel, perceive or be conscious, or to have subjective experiences. Eighteenth century philosophers used the concept to distinguish the ability to think from the ability to feel . In modern western philosophy, sentience is the ability to have sensations or experiences...