Why Are Animals Used to Study the Brain?
Just as animals are used as models to study the heart or lungs of human beings, so they are used as models to gain insight into the human brain and nervous system. But the brain is much more complex and subtle than any other organ. Not only does it control the functions of the rest of the body but it is responsible for movement, communication, memory, perception, emotion—all of the activities encompassed by the general term behavior.
It may seem paradoxical to use animals to study the one organ that most clearly distinguishes humans from animals. Animals, after all, are not capable of many of the more complex functions found in humans, such as advanced language, moral reasoning, or complex learning skills. But many of the basic structures and functions of the brain are common to all animals. Since complex human thoughts are built on a foundation of simpler mental processes that are evident in animals, animal studies can shed light on uniquely human behaviors.
Animal research involving the brain has already produced dramatic improvements in human health and well being, and it promises many more.18 Drug therapies developed in part in animals have revolutionized the treatment of mental illness in the last generation. For example, chlorpromazine, which was developed in the 1950s using animals, and other antipsychotic drugs have eliminated the horrific conditions that used to exist in the wards of mental hospitals where the most severely disturbed patients were once kept. More generally, drugs have proven effective in treating the symptoms of schizophrenia, which affects millions of Americans. Anti-anxiety drugs that have proven of immense benefit in treating human anxiety are developed and tested with animals. Animal tranquilizers have also made it possible to examine and treat livestock, pets, or wildlife that are normally difficult to handle.
In addition, many purely behavioral treatments that do not rely on drugs have been developed through animal research. Behavior modification therapies are the most effective and widely applied techniques for treating alcoholism, drug abuse, obesity, neuroses, compulsions, and phobias. These therapies are partly the result of many years of basic animal research on the fundamental properties of learning and on the effects of reinforcement (either positive or negative) on behavior.
Animals are used in many other kinds of behavioral studies. Animal experiments have produced valuable information on the effects of visual stimulation on brain development, biofeedback techniques, memory loss, programmed instruction in education, aggression, stress, and recovery after strokes or brain injury. We would know much less about these aspects of human life without animal research, and continued animal research is essential if new ways are to be found to cope with behavioral problems. Nonhuman primates are particularly valuable in behavioral research, as they are in a wide range of biomedical research, because of their many similarities to humans.19
Animals can become addicted to drugs and alcohol just as human beings can. In fact, the addictive quality of cocaine was first demonstrated in animals. When humans quit using cocaine, the withdrawal does not cause severe physical symptoms, which has been the traditional measure of addiction. But animal studies showed that if monkeys were given a choice of receiving cocaine or food, they would administer cocaine to themselves to the point of starvation. Clearly they were addicted to cocaine, but the addiction was behavioral, not physical.
Because animals can become addicted to drugs, they provide excellent models of the addiction process. For example, cocaine has been found to block the uptake of a chemical known as dopamine from nerve junctions in the brain. Animal researchers are now investigating several promising compounds that could reduce the craving for drugs or block the effects of drugs in the brain.
Animal studies have also been integral to many of the behavioral therapies that are currently the only proven long-term methods for dealing with drug addiction and other compulsive behaviors. Animals have been used to study the reinforcing mechanisms that promote or discourage certain behaviors. In addition, animal research has illuminated the complicated interactions between addictive behavior and the environment. One example involves an animal model of heroin overdose. If rats are given repeated injections of heroin (morphine) of increasing dosage in the same environment, they develop great tolerance just as humans do. They easily survive a dose that would have been lethal if given first. But if the same heroin dosage is administered to these tolerant rats in a new and novel environment, many of them die. Perhaps the effects of novel environments or new situations account for a portion of the deaths from heroin overdose in human addicts.