Animal experimentation (psychological methodologies)

• TYPE OF PSYCHOLOGY: Psychological methodologies
• Psychologists often study animals and their behavior, sometimes to understand the animal itself and sometimes to learn more about humans. Because there are many biological and psychological similarities between humans and other animals, animal models can be extremely valuable, although it is sometimes controversial.

Introduction

Before the general acceptance of Charles Darwin’s theory of evolution in the late nineteenth century, many in the Western world believed animals lacked emotions or thought. Darwin’s work challenged this view, highlighting the biological and behavioral continuity across species. This shift led scientists to consider animal models for understanding human psychology—a view reinforced by contemporary neuroscience, which finds that all animal brains share fundamental structures, cell types, and signaling systems.

Psychologists who study animals in the twenty-first century typically fall into overlapping categories such as behavioral neuroscientists (formerly called biopsychologists), learning theorists, and ethologists or sociobiologists. These disciplines investigate genetic, neural, environmental, and evolutionary bases of behavior—ranging from lab-controlled studies of learning and memory to field studies of social behavior in the wild. Learning theorists study the learned and environmental controls of behavior, for example, stress, stimulus-response patterns, motivation, and the effects of reward and punishment. Ethologists and sociobiologists concentrate on animal behavior in nature, for example, predator-prey interactions, mating and parenting, migration, communication, aggression, and territoriality.

Animal studies in the twenty-first century are increasingly shaped by the ethical framework of the "3Rs": Replacement (using alternatives when possible), Reduction (using fewer animals), and Refinement (minimizing distress). Technological advances like genetically modified rodents, optogenetics, and high-resolution imaging have improved the precision and efficiency of animal research, allowing for more targeted experimentation and better alignment with ethical standards.

Reasons for Using Animal Subjects

Psychologists study animals for a variety of reasons. Sometimes, they study the behavior of a particular animal to solve a specific problem. They may study dogs, for example, to learn how best to train them as police dogs; chickens to learn how to prevent them from fighting one another in coops; and wildlife to learn how to regulate populations in parks, refuges, or urban areas. These are all examples of what is called applied research.

Most psychologists, though, are more interested in human behavior but study animals for practical reasons. A developmental psychologist, for example, may study an animal that has a much shorter life span than humans do so that each study takes a much shorter time and more studies can be done. Animals may also be studied when an experiment requires strict controls; researchers can control the food, housing, and even social environment of laboratory animals but cannot control such variables in the lives of human subjects. Experimenters can even control the genetics of animals by breeding them in the laboratory; rats and mice have been bred for so many generations that researchers can special order from hundreds of strains and breeds and can even obtain animals that are basically genetically identical to one another.

Psychologists sometimes study animals because certain procedures necessary for understanding the brain—such as invasive or long-term interventions—are not ethically permissible in human research. While animal research has its own ethical requirements, it allows a degree of experimental control not possible in studies involving human participants. Physiological psychologists and neuropsychologists, in particular, may use invasive procedures (such as brain surgery, hormone manipulation, or drug administration) that would be unethical to perform on humans. Without animal experimentation, much of this research simply could not be conducted. Comparable research on human victims of accidents or disease would have less scientific validity and would raise additional ethical concerns.

A number of factors make animal research applicable for the study of human psychology. The first factor is homology. Animals that are closely related to humans are likely to have similar physiology and behavior because they share the same genetic blueprint. Monkeys and chimpanzees are the animals most closely related to humans and, thus, are homologically most similar. Monkeys and chimpanzees make the best subjects for psychological studies of complex behaviors and emotions. However, they are expensive and difficult to keep, and there are serious ethical considerations when using them, so they are not used when another animal would be equally suitable.

The second factor is analogy. Animals that have a lifestyle similar to that of humans are likely to have some of the same behaviors. Rats, for example, are social animals, as are humans; cats are not. Rats also show similarity to humans in their eating behavior (which is one reason rats commonly live around human habitation and garbage dumps); thus, they can be a good model for studies of hunger, food preference, and obesity. Rats, however, do not have a similar stress response to that of humans; for studies of exercise and stress, the pig is a better animal to study.

The third factor is situational similarity. Some animals, particularly dogs, cats, domesticated rabbits, and some domesticated birds adapt easily to experimental situations such as living in a cage and being handled by humans. Wild animals, even if reared by humans from infancy, may not behave normally in experimental situations. The behavior of a chimpanzee that has been kept alone in a cage, for example, may say something about the behavior of a human kept in solitary confinement, but it will not necessarily be relevant to understanding the behavior of most people in typical situations.

By far, the most common laboratory animal used in psychology is the Norway rat (Rattus norvegicus), the first mammal to be domesticated for testing purposes. Originally, the choice of the rat was something of a historical accident. Because the rat has been studied so thoroughly, it is often the animal of choice, so comparisons can be made from study to study. Fortunately, the rat shares many features analogous to humans. Other animals frequently used in psychological research include pigeons, mice, hamsters, gerbils, cats, monkeys, and chimpanzees.

In addition to these traditional mammalian models, many twenty-first-century psychology and neuroscience laboratories utilize non-mammalian species like zebrafish (Danio rerio), fruit flies (Drosophila melanogaster), and nematodes (Caenorhabditis elegans), commonly called roundworms. These animal subjects offer significant scientific advantages: they develop rapidly, are relatively inexpensive to maintain, and are highly amenable to genetic manipulation. For example, zebrafish have transparent embryos and a fully mapped genome, making them ideal for real-time observation of brain development and gene expression. Although these species have simpler nervous systems than mammals, they nonetheless exhibit complex behaviors—including learning, social bonding, and stress responses—making them valuable models for studying fundamental aspects of cognition that may generalize to humans under certain conditions. Innovations such as CRISPR (clustered regularly interspaced short palindromic repeats) gene editing technology and optogenetics allow researchers to precisely manipulate genes or neural circuits in animal models, including in zebrafish. However, the translational gap between animal and human responses remains a key challenge in applying these findings clinically.

Scientific Value

One of the most important topics for which psychologists use animal experimentation is the study of the interactive effects of genes and the environment on brain development and subsequent behavior. These studies can only occur if animals are used as subjects because they require subjects with a relatively short lifespan that develop quickly; they may involve invasive procedures to measure cell and brain activity, or they may require the manipulation of major social and environmental variables in the subject's life.

In the 1920s, Edward C. Tolman and Robert Tryon began a study of the inheritance of intelligence using rats. They trained rats to run a complex maze and then, over many generations, bred the fastest learners with one another and the slowest learners with one another. From the beginning, offspring of the bright rats were substantially faster than offspring of the dull rats. After only seven generations, there was no overlap between the two sets, showing that intelligence is at least partly genetic and can be bred into or out of animals just as size, coat color, or milk yield can be.

Subsequent work with selectively bred rats, however, found that high-performing rats would outperform the slower rats only when tested on the original maze used with their parents and grandparents; if given a different task to measure their intelligence, the bright rats were in some cases no brighter than the dull rats. These studies were the first to suggest that intelligence may not be a single attribute that one either has much or little of; there may instead be many kinds of intelligence.

Over time, researchers developed selectively bred rats as models of many interesting human characteristics. Of particular value are animal models of human psychopathology. For example, genetic lines of rats have been developed that serve as models for susceptibility to depression, anxiety, alcoholism, and attention-deficit hyperactivity disorder (ADHD). These models are important not only in understanding genetic, environmental, and physiological factors associated with these disorders, but also in serving as early tests for possible drug treatments for them. Indeed, the area of behavioral pharmacology, where drug effects on behavior are studied in animal models, is an important and growing area of research.

Brain Studies

Another series of experiments that illustrate the role of animal models in the study of brain and behavior is that developed by David Hubel and Torsten Wiesel, who studied visual perception (mostly using cats). Hubel and Wiesel were able to study the activity of individual cells in the living brain. By inserting a microelectrode into a brain cell of an immobilized animal and flashing visual stimuli in the animal’s visual field, they could record when the cell responded to a stimulus and when it did not.

Over the years, scientists have used this method to map the activities of cells in several layers of the visual cortex, the part of the brain that processes visual information. They have also studied the development of cells and the cell connections, showing how early experience can have a permanent effect on the development of the visual cortex. Subsequent research has demonstrated that the environment has major effects on the development of other areas of the brain as well. The phrase “use it or lose it” has some accuracy when it comes to development and maintenance of brain connections and mental abilities.

Harlow’s Experiments

Perhaps the most famous psychological experiments on animals were those done by Harry Harlow in the 1950s. Harlow was studying rhesus monkeys and breeding them in his own laboratory. Initially, he would separate infant monkeys from their mothers. Later, he discovered that, despite receiving adequate medical care and nutrition, these infants exhibited severe behavioral symptoms: They would sit in a corner and rock, mutilate themselves, and scream in fright at the approach of an experimenter, a mechanical toy, or another monkey. As adolescents, they were antisocial. As adults, they were psychologically ill-equipped to deal with social interactions: Male monkeys were sexually aggressive, and female monkeys appeared to have no emotional attachment to their babies. Harlow decided to study this phenomenon (labeled “maternal deprivation syndrome”) because he thought it might help to explain the stunted growth, low life expectancy, and behavioral symptoms of institutionalized infants which had been documented earlier by René Spitz.

The results of the Harlow experiments profoundly changed the way psychologists think about love, parenting, and mental health. Harlow and his colleagues found that the so-called mothering instinct is not very instinctive at all but is learned through social interactions during infancy and adolescence. They also found that an infant’s attachment to its mother is based not on its dependency on food but rather on its need for “contact comfort.” Babies raised with both a mechanical “mother” that provided milk and a soft, cloth “mother” that gave no milk preferred the cloth mother for clinging and comfort in times of stress.

Through these experiments, psychologists learned how important social stimulation is, even for infants, and how profoundly the lack of such stimulation can affect mental development. These findings played an important role in the development of staffing and activity requirements for foundling homes, foster care, daycare, and institutions for older adults, and individuals with physical or mental disabilities. They have also influenced social policies that promote parent education and early intervention for children at risk.

Although groundbreaking, Harlow’s experiments are now seen as ethically troubling by modern standards. Nonetheless, they played a vital role in reshaping theories of attachment, influencing the development of trauma-informed care, foster systems, and early childhood interventions.

Limitations and Ethical Concerns

However, there are drawbacks to using animals as experimental subjects. Most important are the clear biological and psychological differences between humans and nonhuman animals; results from a study using nonhuman animals simply may not apply to humans. In addition, animal subjects cannot communicate directly with researchers; they cannot express their feelings, motivations, thoughts, and reasons for their behavior. If a psychologist must use an animal instead of a human subject for ethical or practical reasons, the scientist will want to choose an animal that is similar to humans in the particular behavior being studied.

For the same reasons that animals are useful in studying psychological processes, however, people have questioned the moral justification for such use. Because it is now realized that vertebrate animals can feel physical pain and that many of them have thoughts and emotions as well, animal experimentation has become politically controversial.

Psychologists generally support the use of animals in research. The American Psychological Association (APA) identifies animal research as an important contributor to psychological knowledge. The majority of individual psychologists would tend to agree. In 1996, S. Plous surveyed nearly four thousand psychologists and found that fully 80 percent either approved of or strongly approved of the use of animals in psychological research. Nearly 70 percent believed that animal research was necessary for progress in the field of psychology. However, support dropped dramatically for invasive procedures involving pain or death. Undergraduate students majoring in psychology produced largely similar findings. Support was less strong among newer rather than more established psychologists and varied by gender, with women generally expressing more concern.

Some psychologists would like to see animal experimentation in psychology discontinued altogether. In 1981, psychologists formed an animal rights organization called Psychologists for the Ethical Treatment of Animals (PsyETA), later renamed the People for the Ethical Treatment of Animals (PETA). It is highly critical of the use of animals as subjects in psychological research and has strongly advocated improving the well-being of those animals that are used through publication (with the American Society for the Prevention of Cruelty to Animals) of the Journal of Applied Animal Welfare Science. The organization also strongly advocates for human-animal studies, in which the relationship between humans and animals is explored. Companion animals (pets) can significantly impact psychological and physical health and can be used as a therapeutic tool with, for example, people in nursing homes. In this field of study, animals themselves are not the subjects of the experiment; rather, the relationship between humans and animals is the topic of interest.

Surveys in the 2020s continued to show that while many psychologists support animal research, public scrutiny has intensified, especially regarding invasive procedures. Attitudes vary by age, gender, and academic subfield, with younger researchers and women generally expressing greater caution or opposition to animal experimentation.

Regulations

In response to concerns regarding the use of animals in experiments, the US Congress amended the Animal Welfare Act in 1985 to cover laboratory animals as well as pets. (Rats, mice, birds, and farm animals were specifically excluded.) Although these regulations do not state specifically what experimental procedures may or may not be performed on laboratory animals, they do set standards for humane housing, feeding, and transportation. Later amendments extended protections to the psychological well-being of nonhuman primates, prohibited animal fighting, and mandated that laboratories that use dogs for testing provide exercise, among other protections.

In addition, the Animal Welfare Act requires that all research on warm-blooded animals (except those specifically excluded) be approved by a committee before it can be carried out. Each committee (known as Institutional Animal Care and Use Committees, IACUCs) is composed of at least five members and must include an animal researcher; a veterinarian; someone with an area of expertise in a nonresearch area, such as a teacher, lawyer, or member of the clergy; and someone who is unaffiliated with the institution where the experimentation is being done and who can speak for the local community. In this way, those scientists who do animal experiments must justify the appropriateness of their use of animals as research subjects.

The APA has its own set of ethical guidelines for psychologists conducting experiments with animals. The APA guidelines are intended for use in addition to all pertinent local, state, and federal laws, including the Animal Welfare Act. In addition to being more explicit in describing experimental procedures that require special justification, the APA guidelines require psychologists to have their experiments reviewed by local IACUCs and do not explicitly exclude any animals. About 95 percent of the animals used in psychology are rodents and birds (typically rats, mice, and pigeons), which the Animal Welfare Act does not govern. However, they are protected under National Institutes of Health guidelines and must be reviewed by Institutional Animal Care and Use Committees (IACUCs) for federally funded research. Internationally, stricter standards—such as those mandated by the European Union—have influenced ethical practices worldwide.

Alternatives to animal experimentation continue expanding thanks to advances in artificial intelligence (AI), silico modeling, and human-derived organoids. While these methods cannot fully replicate the complexity of living organisms, they offer powerful tools for reducing animal use and improving predictive accuracy. Nonetheless, animal studies continue to play a crucial—though increasingly specialized—role in psychological research. Advances in AI and machine learning enabled sophisticated behavioral simulations, and “brain organoids”—tiny, lab-grown clusters of human neurons—offer promising alternatives for studying neural development and drug response. While these tools cannot yet replicate the full complexity of an animal’s brain or behavior, they complement animal models and reduce the need for large-scale animal experimentation.

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