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On her deathbed, according to her secretary Alice B. Toklas, Gertrude Stein asked, “What is the answer?” Receiving no reply, she continued, “Then, what is the question?”

Human curiosity, and our insatiable impulse to ask questions, drives scientific research. In the July issue of Technology Review, readers had a chance to formulate their own list of the most important unanswered scientific questions. Presented with a list of 14 questions that Carnegie Institution president Maxine Singer and I claimed were among the most important in our book Why Aren’t Black Holes Black? The Unanswered Questions at the Frontiers of Science, nearly 200 readers commented on the list by substituting their own favorite questions for ours. l Most of the respondees agreed with our premise that science, challenged by innumerable fascinating unanswered questions, is far from over. But many readers also identified what they they saw as serious ommisions and a few soundly denounced our list as misguided, elitist, or naive. In short, the survey demonstrated that while scientists are generally convinced that answers are achieved with some degree of objectivity, our choice of questions is highly subjective. Here are what Technology Review readers identified as the most compelling questions facing science today.

The Most Frequently Asked Question

Technology Review readers posed more than 100 different questions, but almost a third of all respondents-by far the largest group-placed questions about the mind, the brain, and the nature of consciousness near the top of their lists. Among the varied questions related to this topic were: How does the mind work? What are emotions? What is love? Can we build a conscious machine? What is the origin of creativity? What do dreams mean? Why do we respond to music?

These questions contrast with our more narrowly focused question: “What are the physical origins of memory?” which one reader described as “almost laughably simple” in comparison with the attempt to understand consciousness. Many of science’s deepest thinkers, including Nobel Prize winners Francis Crick and Gerald Edelman, and mathematician Roger Penrose, would agree with Technology Review readers that the latter “What is consciousness?” is the most fundamental unanswered question concerning the brain. Crick, who defines consciousness as “attention and short-term memory,” has called for an intensified research effort in his book The Astonishing Hypothesis.

But the distinction between questions about memory and those about consciousness raises a key point about the nature of science. For a question to be scientific, it must be answerable through a reproducible process of observation, experiment, and theory. Is the study of consciousness, as opposed to the physical brain, scientific? Many researchers, including Stanford computer scientist Terry Winograd and the late physicist Richard Feynman, are not persuaded that it’s possible to find a concrete physiological definition of consciousness, much less an unambiguous experimental protocol for its study, any time soon. They contend that since a clear research strategy is lacking, consciousness must for the time being lie outside the domain of science.

Indeed, most unanswered questions about human thought seem to fall somewhere in the nebulous realm between philosophy and science. What is an idea? What is an emotion? What does it mean to be curious or to know something? It’s hard to see how these abstract questions can be reduced in any neat way to a collective property of brain tissues, nor is it obvious how to make the giant leap from the concept of thought to a reproducible experiment in the lab.

The problem of consciousness has been pondered by myriad scientists and philosophers, from avowed reductionists who expect that thought and emotion can be explained by neurons alone to skeptics who deny any hope of physical understanding. University of California philosopher David Chalmers adopts a useful intermediate view by dividing the question “What is consciousness?” into what he calls the “easy problem” and the “hard problem.”

The easy problem focuses on mechanics of consciousness: How can humans isolate external stimuli and react to them? How does the brain process information to control behavior? How can we articulate information about our internal state? Neurobiologists have long tackled aspects of these questions, which are amenable to systematic study in much the same way that researchers probe the physical mechanisms of memory. Perhaps, with many decades of intense research, such questions can be answered.

The hard problem, on the other hand, relates to the intangible connections between the physical brain and self-awareness, emotion, perception, and reasoning. How can music evoke a sense of longing, or a poem deep sadness? How does reading a book stimulate curiosity or frustration? What are the physical structures and processes that produce love, fear, melancholy, or greed?

Some researchers believe that, in due time, an understanding of consciousness will follow naturally from research on the physical brain. Others argue for a radically new perspective. Chalmers, for example, makes the startling proposition that consciousness must be accepted as a characteristic of the universe completely distinct from previously recognized physical attributes, such as matter, energy, forces, and motions. Perhaps, he says, consciousness is an (as yet unrecognized) intrinsic property of information.

What is consciousness? For the time being, scholars cannot even agree on what exactly the question means, much less imagine the form an answer might take. For as far into the future as anyone cares to foresee, this greatest mystery of the human mind may remain.

Memories are different; they are more tangible and tightly defined. At one level, memories are a kind of information that can be stored, recalled, altered, or deleted-all familiar tasks in the computer age. It’s conceivable that each memory is stored in the brain as a molecule or set of molecules that carries a message. Alternatively, memories might be hard-wired into networks of brain cells, or maybe they consist of electrical potentials that pervade the whole brain. Whatever the nature of memories, we can hold out the hope that answers will yield to clever and persistent study.

There’s another reason why the quest to understand memory holds a central position in the study of the human brain. Awareness, perception, and thinking depend on receiving information through our senses and analyzing that information in the context of learned patterns of experience-patterns recorded as memories. We cannot be self-aware without a remembered context of existence and personal history. Understanding the physical basis of memories, therefore, is an essential step to knowing what it is to be human-to be conscious of memories.


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