The Wandering Mind

by Michael C Corballis

  Whatever the case, the lack of memory for dreams themselves must be adaptive, because it would not serve us well to confuse our dreams with what has actually happened—although occasionally we do this anyway. Although mostly forgotten, dreams sometimes create an elusive sense of mystical or cosmic presence that can persist, as captured by the Victorian poet Alfred, Lord Tennyson in his poem ‘The Two Voices’:

  ‘Moreover, something is or seems,

  That touches me with mystic gleams,

  Like glimpses of forgotten dreams—

  ‘Of something felt, like something here;

  Of something done, I know not where;

  Such as no language may declare.’

  The cycles of REM sleep are orchestrated by a structure deep in the brainstem called the ‘pons’ (Latin for ‘bridge’). REM dreams are dominated by vision, even though the eyes are closed and vision is normally precluded anyway by darkness. Roughly half also include an auditory component, around 30 per cent feature sensations of movement or touch, and hardly any involve taste or smell. We can dream of walking or running, and even people who have suffered paralysis of the lower half of the body dream of moving freely. Our actual movements, though, are inhibited during sleep. This too was probably adaptive, especially during earlier times, because the body is especially vulnerable to attack while we sleep, and movement might alert night-time predators. The inhibition of movement also prevents us from acting out our dreams in the real world, with potentially disastrous consequences, and it sometimes affects the dream world as well. The sleep researcher Allan Hobson refers to ‘the annoying flaccidity of our legs as we try to run faster and faster to elude the imaginary dream assailant’.

  REM sleep emerges in the foetus, and peaks in the third trimester, when it’s there all the time. But the foetus probably doesn’t dream in any meaningful sense of the word. A little later, but still before birth, NREM sleep and wakefulness join the cycle, and after birth the newborn spends roughly equal time awake, in REM sleep, and in NREM sleep. REM sleep gradually drops away, but settles to about 1.5 hours per night throughout most of our lives—roughly the time you might otherwise spend watching a movie or a TV soap. Dreaming itself, though, may be slow to develop. Preschoolers do dream, but reports suggest that their dreams are simple and static, without emotion and with no involvement of the dreamer. Night terrors experienced by some children are probably not the result of bad dreams, but seem to be induced by the disorientation caused by not being properly awake. David Foulkes found that children under the age of seven report dreams when awakened from REM sleep only 20 per cent of the time, compared with 80 to 90 per cent in adults. Dreams might roughly parallel the development of mental time travel itself. As explained earlier, it’s not until the age of about four that the child can mentally escape the present and envisage coherent scenarios in which they are somewhere else at some other time. At around the age of seven, dreams develop a narrative quality, and incorporate characters that move around, including the child as the dreaming self.

  This slow development of dreaming raises the question of whether non-human animals dream. Many of them do have REM sleep, though. In birds, it seems that only hatchlings go into REM sleep. NREM sleep emerged only in land animals, going back at least to the origin of mammals nearly 200 million years ago, with REM sleep kicking in at around the time marsupials split off some 150 million years ago. But REM sleep really took hold with the emergence of placental mammals from around 50 million years ago. Kangaroos are engaged in REM sleep for only about a tenth of the time that we are. And dog owners claim that their pet dogs dream because of the faint twitching and small noises they sometimes make while asleep by the fire, but we can only guess what they might be dreaming about. It is unlikely, though, that their dreams have the narrative quality of human dreams—although we saw in Chapter 4 that rats seem to dream of perambulating through mazes. More of that later.

  REM sleep is not just a dream machine, but seems to be critically important in regulating temperature. Birds and mammals are warm-blooded creatures, and their body temperatures are internally controlled. The system of temperature control, though, seems to depend uniquely on adequate REM sleep. Rats totally deprived of sleep, or even just of REM sleep, all died through a failure of metabolism and thermoregulation. This could mean that REM dreams are simply an epiphenomenon, a secondary consequence of REM sleep, and of no importance in themselves. They are visited upon us for free, as it were, as a car dealer might throw in a sound system when selling you a new car. Even so, people have always sought meaning in the semi-random hustle of images and feelings that occupy our dreams, although this may be no more valid than finding significance in the pattern of tea leaves or the alignments of the planets.

  The ancient scholars believed dreams were inspired by gods and demons. They also believed they foretold of the future, an idea that persists, and indeed seems almost irresistible. Abraham Lincoln is said to have dreamed about an assassination two weeks before he was shot dead, and Mark Twain told of a dream in which he saw his brother’s corpse lying in a coffin a few weeks before he was killed in an explosion. People often claim to have had premonitions of major tragedies. In 1966, in the small Welsh village of Aberfan, heavy rains caused a landslide which smashed into the village school, killing 139 children and five teachers. John Barker, a British psychiatrist interested in the paranormal, arranged for a newspaper to ask whether any of its readers had had a premonition of the disaster, and received 60 letters from across England and Wales. Over half of them claimed to have had the premonition in a dream.

  It is unlikely that these premonitions are evidence of the paranormal. They may be based simply on knowing that the weather was bad, and the memory for dreams can be later embellished to fit events after they occur. As we have seen, memory for dreams is in any case poor and fragmentary, and as much the stuff of fabrication as of true recollection. As I explained in Chapter 2, even the memory of everyday events is more like a story than a tape recording, or a video. Some people, Eeyore-like, seem to expect disasters to happen any moment, and no doubt dream about them too. Sooner or later their dreams are likely to be fulfilled.

  Bob Dylan, at least, in his song ‘I Feel a Change Comin’ On’, is skeptical. He reckons dreams never work for him even when they are true. You’ve got better things to do than dream.

  Enter Sigmund Freud

  Sigmund Freud, father of psychoanalysis, regarded dreams as the product not of gods or demons, but of the unconscious underworld of the mind. The unconscious harbours the disturbing thoughts, say of sex, fear, aggression, or even murder, that arise from our animal instincts, and which society demands that we suppress. The object of psychoanalysis is to reveal the hidden thoughts of the unconscious so that patients can face the true origins of their neuroses. Dreams, wrote Freud, are ‘the royal road to the unconscious’; they provide a glimpse of thoughts that are normally censored. Even so, those thoughts are still disguised in symbols, which need to be interpreted to reveal what they hide. In Freud’s world, at least, thoughts of forbidden sex seemed to predominate. Weapons or tools may be symbols of the male organ. Going up and down ladders or stairs is symbolic of the sexual act. Complicated machines are ‘very probably’ the male genitals, as are landscapes, ‘especially those that contain bridges or wooded mountains’. ‘Tables, whether bare or covered, are women.’

  The problem, as many have pointed out, is that one can interpret almost anything in sexual terms, and form conclusions that are based more on whim than on the true nature of things. I have tried in vain to think of any object or activity that could not be interpreted sexually. (Suggestions welcome.) Freud’s view that suppressed sexual misadventure underlies neuroses was also a forerunner of the therapies that surfaced in the 1980s and 1990s, and mentioned in Chapter 2. It again exposes the logical error of affirming the consequent. An unfortunate experience with women, for instance, may possibly result in dreams about a table, but one may well dream about a table as a result of
an experience with, well, a table. I have it on reasonable authority that people sometimes dream about sex itself, without symbolic cover.

  That said, Freud’s Interpretation of Dreams, published in 1900, is an insightful and scholarly account of theories about dreams. And he was himself not entirely confident of his interpretations; in a letter to his friend Wilhelm Fliess in 1906 he wrote:

  Do you suppose that some day a marble tablet will be placed on the house, inscribed with these words: ‘In this house on July 24th, 1895, the secret of dreams was revealed to Dr. Sigm. Freud’? At the moment I see little prospect of it.

  Freud also mentions what he calls ‘typical dreams’, which are dreams that recur and seem to be universal. They include dreams of falling from a great height, flying, or being naked. Freud suggests that dreams of falling or flying hark back to childhood, when one is carried and maybe playfully thrown in the air by a parent, or ridden on a playground swing or see-saw. That seems innocent enough. Dreams of nakedness, he says, express a normally suppressed tendency to exhibitionism, but are accompanied by a sense of shame, heightened by the inability to hide one’s nakedness ‘by means of locomotion’. Does this sound familiar? He goes on to say: ‘I believe that the great majority of my readers will at some time have found themselves in this situation in a dream.’

  But perhaps dreams of nakedness derive from being naked as an infant, or reflect the fear of being caught with one’s pants down. Another typical dream, also mentioned by Freud, is that of failing an exam, or being required to repeat a course. Freud suggests that this relates to anxiety over early misdeeds, but later expressed in terms of more contemporary fears. Even so, I still occasionally dream of failing an exam, or more commonly of not having done any exam preparation, but I haven’t had to take an exam for some 50 years. Nevertheless, our early anxieties do seem to persist in dreams. I still dream with trepidation of being back in boarding school, but that’s not a fear that haunts me now in my day-to-day existence (and it wasn’t really that bad). I also dream of being lost in a strange city, which I suppose could happen one of these days—but I don’t lose any sleep over it. Whatever the origins of these typical dreams, though, their universality does suggest they are not merely random, kaleidoscopic jumbles.

  The Freudian idea that dreams are symbolic disguises of shameful or forbidden thoughts has largely lost favour. He was probably right, though, in recognising the unconscious mind, which seems to play a role when consciousness is focused elsewhere. We all know of the ‘Aha!’ experience that pops into our heads well after a conscious attempt to solve a difficult crossword clue or remember someone’s name. The mathematician Henri Poincaré once described how he came upon one of his insights while on a geological excursion:

  The incidents of the journey made me forget my mathematical work. Having reached Coutances, we entered an omnibus to go some place or other. At the moment when I put my foot on the step, the idea came to me, without anything in my former thoughts seeming to have paved the way for it, that the transformations I had used to define the Fuchsian functions were identical with those of non-Euclidian geometry!

  Dreams as simulated threats

  Tyger! Tyger! Burning bright

  In the forests of the night, What

  immortal hand or eye

  Could frame thy fearful symmetry?

  —William Blake, from Songs of Experience

  The Finnish psychologist Antti Revonsuo suggests that dreams are simulations of threatening events, providing the opportunity to develop ways of recognising and coping with real-life dangers. Such dreams emerged during the Pleistocene as an adaptive response to an environment fraught with danger. Blake’s ‘Tyger’, then, is a threat from prehistoric life, perhaps not so much from the forests of the night as from the open expanse of the African savannah. The ‘typical dreams’ referred to above are indeed often threatening, sometimes nightmarish. Dreams do seem to have something of a primeval character—we don’t seem to dream of reading, writing, using a computer, even driving a car. Revonsuo suggests that the dream system harks back to times no longer relevant in the modern world, but is nonetheless ingrained in emotional memory. Dreams seem to have much in common with children’s stories, which are alive with animals, forests and dangerous things. I am led to wonder, in fact, whether we have recreated a primeval world for our children, providing them with the stuff of bad dreams for the rest of their lives.

  Revonsuo’s theory has prompted analyses of a large number of dreams, collected in several different countries. Some two-thirds to three-quarters of dreams include threatening events, which is much higher than the proportion of threats contained in parallel logs of events during waking hours. The threats experienced in dreams are also much more severe. Nevertheless, people actually exposed to threats or real-life traumas have more dream threats than those who lead more tranquil lives. One study comparing dreams across different countries showed the proportion of dream threats to be lowest in Finnish children, at just under 40 per cent. According to the authors of this study, these children had lived all their lives in the most peaceful and stable environment of all the studied children—and perhaps weren’t told scary stories. Among traumatised Kurdish children, in contrast, the proportion was 80 per cent.

  The most common forms of dream threats, at around 40 per cent, had to do with aggression, while the rest were made up largely of failures, and of accidents and misfortunes. Echoing my own dreaming of the fear of exams, the threats encountered in dreams derived more from old memories than from recent events. It appears that the emotional significance of the threat was more potent than its recency. Most dream threats were directed at the dreamer, but in about 30 per cent of cases the threat was directed at significant others, such as close kin, friends and allies.

  The idea that threatening dreams hark back to the Pleistocene does carry some plausibility. In the words of Thomas Hobbes’ Leviathan (1651), early life was ‘nasty, brutish, and short’, and evidence from fossil remains from the Pleistocene indeed reveals a dearth of individuals over the age of 40, in Neanderthals as well as in early humans. For our hunter-gatherer forebears, threats to life must have included dangerous predators and perilous means of getting food. It may well have been adaptive to dream of simulated attacks, and so develop coping strategies. This is not to say that memories of tigers and other predators are encoded in the genome itself, although the sense of danger in unfamiliar places or at the sight of unfamiliar creatures may well have become ingrained in our biological make-up from more threatening times. In children’s stories and cartoons, we seem to do our best to revive the Pleistocene. But not all threats are present in dreams. Another potent threat to life in the Pleistocene was disease, but dream life is not well equipped to find cures for illness or infection. We seldom dream of being ill, and even if we did, there isn’t much the dream could do about it. Dreaming seems calibrated to expose threats in which the dream itself can lead to potential solutions.

  Like Freudian theory, the threat theory seems to suggest that REM dreams, at least, are peculiar to humans or to our Pleistocene forebears, although perhaps tigers had gleeful dreams of threatening rather than being threatened—I should add that the tables have been turned, and the tiger is now the threatened species. The threat theory may be more general, though. REM dreams are driven by processes in the brainstem, which probably well up through the emotional centres before influencing higher areas that carry memories. Our human emotions may have characteristics born of the dangerous environment of the Pleistocene, but emotions themselves have much more ancient origins. Walter Ratty, too, may dream of dangerous cats.

  In his 1872 book The Expression of the Emotions in Man and Animals, Charles Darwin suggests that there is only one emotional expression that seems to be unique to humans. ‘Of all expressions,’ he writes, ‘blushing seems to be the most strictly human’. Now that’s something I’d never have dreamed of.

  The return of Walter Ratty

  The threat theory is based la
rgely on dreams occurring during REM sleep, which are the most vivid and memorable, and also the most frequent. Dreams during NREM sleep, and especially early-night NREM sleep, seem to tell a different story, in which dreams represent recent experiences rather than old emotional fears. In this respect, NREM dreams seem more in line with hippocampal recordings, whether from rats or humans. In Chapter 4, I described how ‘ripples’ of neural activity in the rat hippocampus correspond to trajectories in a familiar terrain, such as a maze. The trajectories may correspond not only to paths actually taken, but also to new paths, perhaps in anticipation of further exploration. These ripples occur both while the animal is awake as well as when it is asleep. It is during early NREM sleep that reactivation of trajectories is strongest.

  Erin Wamsley and Robert Stickgold have studied dreaming in humans during NREM sleep, and around half of these dreams include at least one reference to a recent experience during waking hours. In only 2 per cent of cases, though, did the dream replay the experience as it actually happened. Here’s an example of how a dream can reflect aspects of the experience without actually duplicating it:

  Waking memory source: When I left Starbucks [at the end of my shift], we had so many leftover pastries and muffins to throw away or take home. I couldn’t decide which muffins to take and which to toss . . .