Michael C Corballis. American Scientist. Volume 100, Issue 3. May/June 2012.
So begins James Thurber’s short story, “The Secret Life of Walter Mitty” which was first published in The New Yorker in 1939 and made into a film starring Danny Kaye in 1947. As the archetypal daydreamer, Walter Mitty’s name worked its way into English language dictionaries, not only as a noun but also as an adjective, Walter Mittyish. Of course, Walter Mitty exists in all of us, as our minds wander through landscapes often removed from the humdrum worlds that we actually inhabit. Mind wandering—basically thinking about something other than what is going on around you—seems especially intrusive when we are otherwise inactive, as on a long plane ride or a period of sleeplessness at night. Matthew A. Killingsworth, a doctoral student at Harvard University, and Daniel T. Gilbert, a professor of psychology at Harvard, reported in Science that people’s minds might wander nearly half of the time. Some of the mechanism of mind wandering emerges from cognitive neuroscience, especially in brainimaging research.
In the 1920s, German physician Hans Berger unveiled the first hint of activity in the brain during resting states. His work arose from an episode in which he fell from a horse and landed in the path of a horse-drawn cannon. He escaped injury, but his sister at home several kilometers away sensed that he was in danger and asked her father to contact him. Berger took this as evidence of telepathy, which he thought might depend on some physical transmission of “psychic energy” and might be measurable. In 1924, he recorded electrical activity from two electrodes placed under the scalp, one at the front of the head and one at the back, thereby inventing electroencephalography (EEG). With the subject resting, eyes closed, the EEG revealed rhythmic activity with a frequency of 8-13 Hertz, or cycles per second, which became known as “Berger ‘s wave”—now called alpha waves. When the eyes open, faster beta waves suppress the alphas. In later developments of EEG, multiple electrodes on the surface of the scalp provided information about the locus of the activity within the brain.
Better techniques for localizing activity in the brain also emerged. In the 1970s, the Swedish physiologist David H. Ingvar and the Danish physician Niels A. Lassen injected a radioactive substance into the bloodstream and tracked its course in the brain with external monitors. The blood flows to regions where neural activity is high, and Ingvar noted especially high activity in the frontal areas of the brain during resting states. He described this as representing “undirected, spontaneous, conscious mentation.”
Today, sophisticated methods of tracking blood flow and superimposing it on detailed anatomical images of the brain provide much more precise maps of brain activity while people perform simple tasks. One technique, known as positron emission tomography (PET), also uses the injection of radioactive substances in the bloodstream, and a less invasive technique known as functional magnetic resonance imaging (fMRI) uses a powerful magnet to detect hemoglobin, which is carried by the blood. Both techniques deliver detailed structural images of the brain with the movement of blood superimposed on it. Clinical researchers use these techniques to investigate brain pathology, and fMRI in particular is increasingly used to investigate the brain network involved in normal thought processes, such as reading, processing faces or remembering lists of words.
At first, some scientists expected to engage an experimental subject in some task, record brain activity and subtract from it the activity of the brain at rest to discover the brain areas specifically activated by the task. To their surprise, activity appeared in wider regions of a brain that is supposedly at rest than one engaged in a task. That is, when subjects are instructed to think of nothing in particular, brain activity is widespread, but when they are engaged in the task at hand the activity tends to be restricted to specific regions.
Scientists named brain regions active during the supposedly resting state as the default network. This network includes regions in the prefrontal, temporal and parietal regions of the brain. Traditionally, brain scientists called these association areas, suggesting that input enters the brain through sensory areas and output exits through motor areas, with the association areas providing the interconnections that constitute thought. This implies a rather passive view of the brain as an input-output system, with some associative processing in between. The notion of a default network that is active even when there are no inputs or outputs suggests a more dynamic model. As Ingvar put it in 1979:
On the basis of previous experiences, represented in memories, the brain—one’s mind—is automatically busy with extrapolation of future events and, as it appears, constructing alternative hypothetical behavior patterns in order to be ready for what may happen.
Wandering Across Time
Mind wandering can serve useful functions, and it’s not always spontaneous. Mental time travel, as Ingvar suggested, makes up one of those functions. Recent studies explore this phenomenon by having people recall specific episodes from past experiences or imagine episodes that might happen in the future. One way to do this starts with asking each experimental subject to compile a list of past episodes, in each case specifying a person, an object and a location. For instance, a subject might remember her friend Liz dropping her laptop in the library, her sister falling off her bicycle in the park, or her partner Tom trying to cook pancakes in the kitchen. With such a list compiled, a researcher places the subject in an fMRI scanner and provides a location, person and object—such as library, Liz and laptop—to prompt the subject to recall the corresponding episode. This is the memory phase of the study, involving mental travel back in time.
To measure activity when people imagine future episodes, the subject receives prompts from the listed past episodes that are rearranged into new combinations, such as kitchen, Liz and bicycle. Then, the researcher asks the subject to imagine a future episode involving this combination. This task represents mental travel forward in time.
The brain activity elicited by the recovery of past episodes resembles that elicited by imagined future ones. Both involve activity within the default network, including the prefrontal and parietal lobes, as well as in the hippocampus, which is located on the inside surface of the temporal lobe and is known to be crucial to memory. Moreover, damage to the hippocampus causes amnesia for past events and impairs the ability to imagine future ones. One dramatic case is the English musician Clive Wearing, who suffered severe amnesia following a viral infection that destroyed part of his hippocampus in 1985. Deprived of the memory for past episodes or the ability to imagine events that might happen in the future, he lives in the present, constantly under the impression that he has just woken up, or risen from the dead. His plight is vividly described in his wife Deborah’s book Forever Today, and in the United Kingdom’s ITV television documentary titled “The Man with the 7-Second Memory.”
This is not to say that the brain regions for recalling the past are identical to those active in imaging the future, for if this were so we would be unable to distinguish our memories from our fantasies. Nevertheless, the overlap is extensive, and the differences are small and subtle. In our experience of events in time, moreover, there is continuity between future and past, as future events loom and move seamlessly into the past, like oncoming traffic. As the Queen in Lewis Carroll’s Through the Looking Glass remarked, “It’s a poor sort of memory that only works backwards.”
Even people without amnesia possess notoriously unreliable memory for episodes. We remember only a tiny fraction of the events in our lives, and those we do remember are often distorted or recalled inaccurately. Indeed, recalling the past often includes as much construction as imagining the future. As the late Ulric Neisser, long a cognitive psychologist at Cornell University, wrote: “Remembering is not like playing back a tape or looking at a picture; it is more like telling a story.” Clearly, some “memories” are almost entirely false. Elizabeth Loftus, a pioneer in the study of false memories from the University of California, Irvine, vividly recalls discovering her mother lying dead in a swimming pool. It turned out that the memory was false. Loftus was in fact asleep at the time her mother’s body was discovered, by her aunt. The adaptiveness of our episodic memories may therefore have relatively little to do with forming a diary-like record of our past, and more to do with providing scenarios from which to build possible future episodes, and perhaps with creating gratifying self-images. Men who served in wars, for example, might remember acts of heroism that were in fact less heroic than remembered, or perhaps did not occur at all. In his presidential campaigns, Ronald Reagan often spoke of wartime heroics, but at least some of the episodes he described actually came from old movies. Hillary Clinton recently told of landing in Bosnia in 1996 under sniper fire, but television records show her being greeted in peace by a smiling child.
Of course imagined future events arise from pure fabrication, in the sense that they have not yet occurred, and indeed might never occur. This suggests that the network underlying mental time travel concerns fiction as much as fact, referring to events outside of the subjective timeline. We are inveterate storytellers, whether around the campfire or in the local pub, in novels or short stories, in movies and soap operas, even in malicious gossip. The literary biographer and critic Brian Boyd argued that fiction is a form of play, enabling us to hone our social skills and our ability to handle the exigencies of life.
Wandering into Another’s Mind
Another form of mental travel takes us into the minds of others. This is known as theory of mind. For the most part, we know what others think or believe, and calibrate our behavior accordingly. Theory of mind also plays an important part in fiction, and stories are often told from the perspective of others. One way to test theory of mind is the so-called false-belief test. If one person understands that another person has a different belief—different from what most people know to be the true state of affairs—then the first person has knowledge of what is in that other person’s mind.
Such tests have been conducted in the brain scanner to determine which parts of the brain are involved. In one study, people read stories on a screen, some of which involve false belief. One story might describe John telling Emily that he drives a Porsche, but his car is in fact a Ford. Emily knows nothing about cars, and so she believes that John’s car is a Porsche. Emily then sees the car, and the subject in the scanner is asked what Emily thinks is the make of car. Most people understand that Emily falsely believes it to be a Porsche. When the subjects read this story, activity within the default network, and especially in the junction of the temporal and parietal lobes, increases markedly relative to the activity elicited by stories that do not involve false belief.
Mind wandering through time and into the minds of others might also bear on another ubiquitous human phenomenon—language.
Minds Meeting in Language
The two classic language areas in the brain—Broca’s area in the prefrontal cortex and Wernicke’s area in a region overlapping the parietal and temporal lobes, as well as the connections between these two areas—lie within the default network. In most people, these areas lie predominantly in the left side of the brain, suggesting that the specialization for language lies primarily in the leftward portion of the default network. Of course, verbal capabilities often play some part in our mind-wandering and mental excursions in time, but we can recollect past events or imagine future ones in visual or auditory terms without involving language at all. Language proves most crucial in communicating mental travels to others. By sharing our experiences and plans, we are vastly better adapted to the complexities of our social lives and to the physical worlds that we have created or colonized.
Language exquisitely conveys the nonpresent. Our brain evolved the ability to register a multitude of concepts to represent objects, actions and qualities, which enable us to create combinations of these to represent episodes. Moreover, we invented symbols, whether words or manual signs, to attach to these concepts. In speech, at least, these symbols are largely arbitrary. For instance, the word hippopotamus—despite being a rather large word—does not resemble, spoken or written, that large animal. Signed languages include a more obvious iconic component, but resemblance of the sign to what it represents is not a necessary quality, and many signs are opaque to nonsigners, or even to those who know a different sign language. Grammar might be understood as a system for combining these symbols to convey episodes, whether remembered or imagined, to others who share the same linguistic conventions. We also use markers of time and place to indicate when and where episodes occurred or will occur. Of course language includes other conventions as well, to indicate such aspects as conditionality, uncertainty, emotion or volition.
Language also allows us to communicate as if through the minds of others. I can imagine how the world looks through the eyes of my granddaughter and perhaps use this perspective to write a children’s story, and novelists are skilled at portraying events through the minds of fictional characters. William Boyd’s prize-winning novel Brazzaville Beach, for example, is told through the first-person eyes of a woman.
Language, though, depends on theory of mind in a more fundamental way. The 20th-century British philosopher Paul Grice pointed out that effective discourse requires that the speaker knows not only what is in the mind of the listener, but also that the listener knows that the speaker knows this. Much of conversation then proceeds as a kind of shorthand, prompting a common stream of thought between speaker and listener. Dan Sperber, director of the web-based International Cognition and Culture Institute, and Gloria Origgi, a philosopher at Centre National de la Recherche Scientifique in Paris, give the example of the utterance: “It was too slow.” This could refer to recent economic developments, a movement of a symphony, the speed of a car, a lecture—and many other things. In context, though, speaker and listener usually have no need to spell out the meaning in more detail. Even in legal documents or sets of instructions to perform some complex task, language is seldom fully explicit. It requires the meeting of minds beyond the level of the words themselves. At the same time, though, language is part of the mechanism by which we come to know and influence what’s in the minds of others. Language allows different minds to wander together.
The extent to which mind wandering exists in nonhuman species is a matter of some contention. Monkeys possess a network somewhat homologous to our default network, and some scientists believe that other primates, and even birds, perform mental time travel and employ theory of mind. Nevertheless, the capacity for mental time travel, recursive mind reading and expressive language appear especially highly developed in our own species, reflecting pressures to create a more elaborate and comprehensive social structure in order to survive the rigors of life on the African savannah during the Pleistocene, dating from some 2.6 million years ago. During that era, the brain increased in size approximately threefold, perhaps establishing a more extensive mental landscape in which our minds can wander.
Perhaps the sense of time, and our obsession with it, distinguishes us most of all from even our nearest relative, the chimpanzee. In The Spectator on April 10, 2010, Freddy Gray quoted Jane Goodall, who studied wild chimpanzees in Gombe Stream National Park in Tanzania for some 45 years, as follows:
What’s the one obvious thing we humans do that they don’t do? Chimps can learn sign language, but in the wild, so far as we know, they are unable to communicate about things that aren’t present. They can’t teach what happened 100 years ago, except by showing fear in certain places. They certainly can’t plan for five years ahead. If they could, they could communicate with each other about what compels them to indulge in their dramatic displays. To me, it is a sense of wonder and awe that we share with them. When we had those feelings, and evolved the ability to talk about them, we were able to create the early religions.
Some suggest that other species, including apes, might indulge in mental time travel, but that we cannot know about their mind wanderings because they lack a language to express them. This argument, however, can be reversed: Perhaps, humans invented language because we wander mentally in time. Goodall suggests that chimpanzees can learn sign language, but their signing is far inferior to human language, especially with respect to telling stories or sharing episodes. In short, the impoverished communication of other primates might reflect precisely their mental confinement to the present.