Continuing our series of Big Science Questions, Chris Bunting asks what makes people violent, while Dolf Zillmann (bottom) reviews the role of brain structures.
A solitary matador and a half-crazed bull replayed their parts in an old, violent ritual in a sun-soaked arena in southern Spain. It was the summer of 1964, but film of the incident is still shown in lecture halls today. As the bull bore down on the unarmed man, it became apparent that the red cape was not being wielded with the usual bullfighter's poise. It was limp and motionless. In fact, the man in the centre of the ring, the brain scientist Jose Delgado, had never faced a charging animal in his life.
But the horns never reached the doctor. Seconds before impact, Delgado flicked a switch on a small radio transmitter he was holding and the bull immediately braked to a halt. He pressed another button and it meekly turned to its right and trotted away.
Delgado was triumphant. After 15 years studying the workings of the brain, he had proved in the most dramatic fashion that understanding and controlling its mechanisms had reached a refinement that allowed an animal's aggression to be turned on and off by remote control. He explained that he had been playing with monkeys and cats "like little electronic toys", making them fight, mate and go to sleep using the same technique of inserting probes in the brain and electrically stimulating relevant tissues.
"A turning point has been reached in the study of the mind," he announced. "I do believe that an understanding of the biological bases of social and antisocial behaviours and of mental activities, which for the first time in history can now be explored in a conscious brain, may be of decisive importance in the search for intelligent solutions to some of our present anxieties." It was the high point of scientists' belief in their ability not only to explain but to intervene in the workings of the brain and in their ability to prevent antisocial aggression.
Today, Delgado and his contemporaries are still an inspiration to many scientists. Felicity Huntingford, an expert on animal aggression at Glasgow University, describes the Yale University academic as "a pioneer and a brilliant science communicator who showed us what could be done. He started a lot of people on this path."
But there was a dark side to the mid-20th century's boundless confidence in the potential for physiological explanations and treatments for brain processes, Huntingford says. In the 30 years preceding Delgado's display, an estimated 40,000 to 50,000 people were lobotomised in the United States alone, often to prevent abnormal aggression.
Walter Freeman, the relentless populariser of the treatment in the US, was confident that pushing a medical "ice pick" into patients' brains and destroying tissue near the thalamus, an area of the brain that he believed was responsible for emotional over-excitement, would help remove the causes of aggression and a range of other problems. There was little proof for his theories, but thousands of people were turned into vegetables by the operations (including, famously, John F. Kennedy's sister, Rosemary).
Controversy has since raged about more academically respectable treatments, such as that proposed by the neurosurgeon Vernon Mark and psychiatrist Frank Ervin in 1970. In Violence and the Brain, they claimed, like Delgado, to be able to determine with precision the parts of the brain responsible for aggression. They said behaviour improved greatly once "problem areas" had been destroyed using electrodes, although others thought serious brain damage was the main result. Chemical methods of reaching these areas, such as the so-called chemical lobotomy drug Thorazine, have provoked similar passionate disagreement.
Why do lobotomies, chemical lobotomies and similar treatments prompt such disquiet? After all, they have been highly effective at treating aggression. There is, however, something profoundly disturbing about the smiling zombies that Freeman and others were often responsible for creating.
"What people did not, and some still do not, seem to understand is that our capacity for aggression and other mental processes are tremendously complex and intertwined with each other," Huntingford says. "It is not a question of just removing this bit of a brain and fixing a problem. You are dealing with something that is very close to the centre of what makes us what we are."
Anthony Burgess made the point in A Clockwork Orange, in which, in successfully treating the protagonist's aggression with aversion therapy, a crucial part of his humanity is eradicated. For Burgess, man was fundamentally both "gloriously creative and bestially destructive". It was impossible to have one without the other.
Understanding of the physiology of the brain has come a long way since Freeman's phrenology. Recent research has focused on neurotransmitters, chemicals that transmit messages between brain cells, and specifically on serotonin, a transmitter that seems to be strongly related to aggressive behaviour. Studies have found that giving animals drugs that lower serotonin levels sometimes makes them more aggressive and that increasing levels can have the opposite effect.
But the role of serotonin is not straightforward. The brain has at least 14 serotonin receptors, and researchers are not sure what role each plays. Levels of the neurotransmitter are also associated with problems such as depression and eating disorders, and the behaviour of some of the receptors is highly complex. One receptor, known as 1B, seems to decrease aggression in mice and monkeys when activated. However, the effect is associated with a lowering in serotonin levels rather than the expected increase.
Another series of studies associating the neurotransmitter vasopressin with aggression has further muddied the waters, indicating that aggressive behaviour may be governed by a complex interplay of chemicals in the brain.
Genetic research has revealed a similarly confusing picture. There have been dramatic results. One study traced a history of extreme violence in a Dutch family back to defects in a gene governing the breakdown of neurotransmitters. But strident headlines claiming that researchers are about to identify aggression genes ignore difficulties in interpreting these results. A lab experiment on mice, for example, could show an increase in fighting because a gene that governs their sense of smell has been disabled - the animals could be unable to use pheremones to signal to each other and therefore avoid conflict.
Another set of researchers insists that such mice studies are of little use in understanding human violence. Adrian Raine at the University of Southern California believes our highly developed prefrontal cortex, which is tiny in lower mammals such as mice, has a vital role in governing aggression. Research has shown that murderers have unusually low levels of glucose metabolism in their prefrontal cortex, indicating problems in that part of the brain.
Despite this research, it is an illustration of the complexity of the subject that most theories of aggression do not even look at the physical make-up of the brain. Approaches since the 1920s have ranged from Sigmund Freud's theory that aggression is an externalisation of every human's death wish and exists with or without external provocation, to Konrad Lorenz's conclusion, based on ethological studies of fish and birds, that it is a drive shared with most of the rest of the animal kingdom.
One of the most fertile approaches, contradicting the tendency of biological theories to concentrate on the brain state of individuals, has looked at the crucial role of social forces in motivating and governing aggressive behaviour. Consider the causes of the terrorist attacks on the World Trade Center and Pentagon in September 2001. Some of the suicide bombers might conceivably have had low levels of serotonin, but religion, culture, ideology, history and the influence of authority all seem to be more directly relevant in explaining why they killed so many people.
Humanity's capacity for intellectual thought, learning and complex communication has often been used to elevate us above animals, but these qualities may also contribute to aggressive behaviour. Studies have found that children who are shown violence are much more aggressive when provoked than those who have been exposed to pacific behaviour. A review in 1994 of 35 years of research into the relationship between western television's violence and aggression found a significant positive correlation. Meanwhile, traditional societies on Tahiti and among the Inuit are reported by anthropologists to show little antisocial aggression because of strong cultural disapproval of aggressive behaviour.
The social learning researcher Albert Bandura even questions the relevance of the concept of aggression to understanding much of man's inhumanity to man. "What I am really interested in is not aggressive feelings but moral standards and how very skilled we are at disengagement from these. That seems to be the real determinant of whether we will harm someone: whether we have removed them from moral consideration."