(pp. 28-32) by John Horgan © 1999 by John Horgan.Used with permission of The Free Press.

Getting in Touch with Emotions

Even if they unravel the mechanisms underlying working memory and other cognitive functions, neuroscientists must face another problem: How does emotion fit into the puzzle?

Until recently many neuroscientists sought to sidestep emotion in their experiments, treating it as an annoying source of experimental noise and distortion rather than a fundamental part of human nature. Neuroscientists have followed the lead of cognitive scientists, who have tried to understand those information-processing functions that can be most easily duplicated in computers, such as vision, recollection, speech recognition, and reasoning.

By avoiding emotion, neuroscientists and cognitive scientists have created a peculiarly one-dimensional picture of the mind, according to Joseph LeDoux, a neuroscientist at New York University. Cognitive science "is really a science of only a part of the mind, the part having to do with thinking, reasoning, and intellect," LeDoux complained in his 1996 book, The Emotional Brain. "It leaves emotions out.

And minds without emotions are not really minds at all. They are souls on ice - cold, lifeless creatures devoid of any desires, fears, sorrows, pains, or pleasures." Fear is a biological phenomenon, with deep roots. LeDoux, himself a cool, controlled man with deep-set eyes and a carefully trimmed beard, has demonstrated that at least one emotion, fear, can be approached empirically. Unlike language or other cognitive functions unique to humans, LeDoux pointed out, fear is a biological phenomenon whose roots reach back far into the history of life.

The neural circuitry and processes that underlie fear have been highly conserved through evolution; thus experiments on rats and other animals may reveal much about humans. The amygdala, which is crucial to the fear response, is found not only in humans and primates but also in rats. "The fear system is very, very simple," LeDoux told me. "You've got a stimulus that comes in through standard input channels, goes to the amygdala and goes out through the output channels," he said.

Early studies of fear responses had produced confusing results because the experiments were too complex. "Every time you change the experiment, you change the way the brain accomplishes the task. So the key in figuring out the fear system is to strip it down to a simpler model." Minute damage to the amygdala interferes with the "freeze" response.

LeDoux has carried out experiments in which rats have been conditioned to associate a certain sound, such as a musical tone, with an unpleasant sensation, such as an electric shock. The initial response of rats and many other animals to such a stimulus is to freeze, an appropriate tactic for an animal threatened by a predator. The freeze response is an innate, reflexive function. LeDoux and his colleagues showed that damage to a minute structure within the amygdala, called the lateral nucleus, prevented rats from learning to freeze in response to the tone preceding an electric shock. The cognitive ability of the rats was unimpaired in other respects.

LeDoux was trying to unravel the circuitry required for more complex fear-related behavior, which is sometimes called instrumental learning. For example, when a rat learns that freezing does not prevent him from being shocked, he tries avoidance - moving to a different part of the cage or climbing up its sides. At this point, the rat makes the transition from being an emotional reactor to an actor, LeDoux said, capable of making choices and trying different strategies.

Physiological symptoms of fear precede, and initiate, the subjective sensation. Psychologists once believed that the subjective sensation of fear is the first component of the fear response; increased heart rate, sweating, and other physiological symptoms were thought to be triggered by the subjective sensation. LeDoux contended that the opposite is probably true; physiological symptoms occur first and then initiate the subjective sensation of fear. In many cases, moreover, the fear response might never generate a conscious sensation.

Our conscious, subjective feelings "are red herrings, detours, in the scientific study of emotions," LeDoux has written. LeDoux felt that too much attention had been paid to consciousness lately. "It would surely get you the Nobel Prize if you figured it out," he told me, "but I don't think it would tell us what we need to know" about the mind. Although consciousness is often equated with the mind, most mental processes occur beneath the level of awareness, LeDoux pointed out.

Consciousness, moreover, is a relatively recent innovation of evolution. "Basically the brain is unconscious. Somewhere in evolution consciousness evolved as a module. It's connected up to some other parts of the brain, but not the rest of it." Nature and nurture speak the same synaptic language. Explaining consciousness is not as important as understanding how the brain draws on both genes and experience to create a self, a personal identity, in each individual. "That to me is the big question: how our brain makes us who we are.

Explaining consciousness wouldn't explain that." The key to this issue is understanding how both nature and nurture affect the brain's wiring. "What's often overlooked is that nature and nurture speak the same language, which is the synaptic language," LeDoux said. Ultimately all influences on personality, genetic or experiential, become manifest at the level of the connections between neurons.

LeDoux doubted whether any single theory would account for emotion. There are many aspects of emotion, he noted. "There's an evolutionary component, there's a cognitive component, a behavioral component. It's just a question of what the balance in the particular situation is." Cognitive theories tend to focus on conscious emotional processes; evolutionary theories emphasize innate emotional responses; behavioral theories stress the role of environmental conditioning. "In any particular emotional episode, it's not a matter of which one is right but which one explains which part of the episode." Moreover, each emotion probably requires a separate explanation; the mechanisms underlying fear are probably quite different from those underlying lust or hatred.

LeDoux summarized the research that he and others have done on emotion, and particularly fear, in The Emotional Brain. He also cautiously suggested that investigations of the neurobiology of fear might at some point yield better treatments for human anxiety disorders. LeDoux expected psychiatrists to dismiss his rat experiments as irrelevant to their work. But to his surprise, psychiatrists responded to his book enthusiastically - almost too enthusiastically, LeDoux suggested. "It's been almost this uncritical acceptance," he explained. "'Yes, let's go! This is the answer!' They seem so desperate. I don't think I have the answers in my book. I just threw out some ideas." "There is as yet no neuroscience of personality."

Like Gerald Fischbach, Torsten Wiesel, and other leading neuroscientists, LeDoux readily acknowledges the shortcomings of his field. He once stated, "We have no idea how our brains make us who we are. There is as yet no neuroscience of personality. We have little understanding of how art and history are experienced by the brain. The meltdown of mental life in psychosis is still a mystery. In short, we have yet to come up with a theory that can pull all this together. We haven't yet had a Darwin, Einstein or Newton." Then LeDoux suggested that neuroscience might not need a unifying theory: Maybe what we need most are lots of little theories. It would be great to know how anxiety or depression works, even if we don't have a theory of mental illness.

And wouldn't it be wonderful to know how we experience a wonderful piece of music (be it rock or Bach), even in the absence of a theory of perception. And to understand fear or love in the absence of a theory of emotion in general wouldn't be so bad either. The field of neuroscience is in a position to make progress on these problems, even if it doesn't come up with a theory of mind and brain.

John Horgan is a freelance writer and author of The End of Science, a U.S. best-seller that has been translated into ten languages. His awards include the Science Journalism Award of the American Association for the Advancement of Science (1992 and 1994) and the National Association of Science Writers Science-in-Society Award (1993)