Here’s a curious phenomenon; maybe you’ve experienced it.

For several years in my mid-twenties I spent my summers tree planting in northern Ontario. It was a difficult job. Every morning at 5 a.m. some classic rock anthem would blare out across the makeshift camp and we’d drag ourselves from our warm tents and pile into the rusted yellow school buses idling on the logging road. Out on “the block,” we were assigned huge chunks of napalmed land, uneven mixes of charred duff, swamp, and scraggly brush. For eleven hours we’d plant little eight-inch saplings—kick-shovel-draw-bend-insert-stomp, kick-shovel-draw-bend-insert-stomp—little mechanical humans jerking along the horizon. Every seven feet, several hundred an hour, several thousand a day. It was fantastically tedious,made worse by bone-chilling drizzle, a fog of biting blackflies, hidden wasps’ nests, thickets of sharp sticks, and patrolling bears who’d ransack our lunches and terrorize the cooks.

Beginner planters spent their time in an agony of unhappiness and frustration. But as the weeks wore on the privations lessened, in part because we became habituated to the job, but also because of an odd recurring experience that some of us discussed among ourselves. I remember the day it first happened to me. It was still early, a little after 9 a.m. I had just loaded up my bags with trees and stood gazing out over the denuded expanse of earth and rubble. I sighed, looked down at my shovel, and began planting. When I raised my head I noticed the sun was on the other side of the sky. Little green spruce dotted the landscape all around me, and on the road empty tree containers sat in a disorderly pile. My watch said 2 p.m. Five hours had passed and I remembered nothing. What happened?

I had no idea, but like other planters before me I welcomed the state. Now days alternated between time-crawling now-ness, idle daydreams—another important consolation—and these strange absences, little wormholes in time where we dropped off the land and reappeared several hours later.

One day I experienced a new variation. I mounted a steep ridge and there, towering before me, was an enormous white pine with silver scales and a broad, knotted trunk. The tree was wrapped in a gauzy halo of needles, and in the late-afternoon sun they filled with golden light. I caught my breath and everything went suddenly very still. The background chatter of the forest faded, and I had the feeling that time had paused, except, in contrast to my wormhole experiences, “I” remained to witness the ellipsis. But it was not an “I” I recognized. As strange as it may sound, I felt as if I were somehow part of the tree. I stood transfixed, a large, unblinking eyeball. And then the feeling passed. In front of me was just a tree. I looked down and continued planting.

The experience of tree planting didn’t end at night. As soon as our eyes closed, a slow-moving landscape flickered up on our retinas and we watched reruns of the day—kick-shovel-draw-bend-insert-stomp, kick-shovel-draw-bend-insert-stomp. I remember being struck by the photographic perfection of these images, bright visuals that were often accompanied by the physical sensation of movement, like that wobbly sea-legs feeling you get after a day of sailing. Once fully asleep, the activity seemed to rev up a notch. I dreamed of twisting in my sleep so I could plant my bedroll, or trying to slam my shovel through the asphalt of an endless dream highway. I often woke in the night protesting: it isn’t fair, this isn’t my workday, this is my time off. I shouldn’t have to plant now! When I struggled against the dream narrative I inevitably woke myself up, though several times I flickered into momentary self-consciousness in the dream itself, and stood there in the empty expanse of dream land with my dream shovel in my hand thinking this was a really weird situation, I’d have to remember to tell someone. Inevitably I woke exhausted, and on the bumpy ride out to the block, all of us muttered about our diabolically doubled workloads.

Tree planting got me thinking about consciousness because the unvarying sameness of the days provided a perfect backdrop for alterations. I noticed the differences, and they seemed to correspond to shifts more fundamental than those of mood or even alertness. In the previous few paragraphs I’ve described seven distinct states of consciousness that most of us have likely experienced at some time or another: general alertness, daydreaming, deep absorption, a heightened present, sleep-onset imagery, dreaming, and the very beginnings of a lucid dream. Some of these occur with strict regularity, others are more rare. And although a few of them may sound mystical, one of the main preoccupations of this book is how far science has come in shedding light on their character.

Until that summer, my conception of consciousness was little more than a crude on/off switch in my head. We were awake, and then we were asleep. Sure, there were dreams, but these sort of happened off the record. Unless you wanted eye rolls and public derision, you only told your bed-partner about them (“I opened the umbrella and out flopped a half-dozen pale cow udders—can you believe that?”). Clearly there was more to consciousness than these two options—how many variations were there, exactly?

The answer, of course, is billions—as many variations as there are individuals to experience them, and within each individual a succession of seemingly unique moments. This disorienting plentitude seems all but impossible to quantify, for the one thing we can say with certainty about consciousness is that it is an ineffably private and subjective affair.

Except that isn’t the full story. Because underneath our shifting tides of awareness are specific—and regular—physiological changes occurring in the brain. The most elemental of these are the circadian processes that govern our sleep-wake cycle. These undulating rhythms form the basic contours of subjective consciousness; they guide changing levels of alertness through each day and, in concert with their chemical emissaries, move us through the various stages of sleep at night.

The notion that sleep is not a single monolithic state is perhaps not fully appreciated by most people. We cycle through stages, of which slow-wave and REM sleep are the most distinct. Each of these two states is as different from the other as they are from waking. This is the case regarding: 1) their specific functions; 2) the physical processes that form them; and 3)—crucially, for the purposes of this book—what they feel like to experience. These three states of consciousness—slow-wave sleep, REM sleep, and waking—form the primary compass of human experience.

This psychological and neuroscientific and experiential story of how consciousness changes over twenty-four hours is the first story I want to tell, and it forms the loose skeleton of this book. But there is a larger, more important story, one that involves some of consciousness’s more dramatic variations, because overtop and between these three primary states, the mind is capable of visiting some very strange destinations. Since I can’t reliably talk about the shifting experience of consciousness without test-driving some of those changes myself, I have gone on six adventures, six major head trips that ended up challenging everything I thought I knew about the expanse of consciousness and how our minds relate to our brains.

...

The Head Trip emerged from my interest in sleep, and so the first adventures I go on involve sleep and dreaming; the narrative begins at night. Yet something very interesting came out of this approach. I came to realize that in a number of important ways, in order to understand day consciousness properly, night is the best place to start. The forces that shape dreaming consciousness do not suddenly vanish when the sun rises; rather, they go underground, and wield their mysterious influence from below. Day mirrors night in ways few people appreciate. Once you acquire this slightly eerie holistic perspective, it becomes very hard to shake.

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Which brings me to a caveat before we get on the wheel. As my friend Matt says, trying to draw strict borders around consciousness is like trying to stick Post-it notes on the ocean. You just can’t do it; the oceanic flow and overlap of consciousness is its most fundamental property. The changes I detail happen along a fluid continuum, and the wheel I imagine describes shifting tendencies within consciousness more than it does fixed stops.

Having said that, one thing is certain: consciousness exists in more wildly varied and abundant forms than simple waking, sleeping, and dreaming. By describing some of its different stations, I hope not only to give you some insight into the biological and psychological processes that underlie our changing experience of consciousness—to reveal, as it were, some of the operating rules of the Self—but also to show why this matters. When I set out on my adventure I wanted to discover what these states might have to teach us about our own habits of mind. In this I wasn’t disappointed. I eventually came to see not only that we have far more agency over our changing mental states than most of us suspect, but also that each of these states taps into its own unique blend of knowledge and insight. In a sense, each destination around the wheel of consciousness has its own local language and customs.

Thus this book is also a travel guide, a trip into our own wheeling heads.

--From The Introduction