Michael is an American author, journalist, and humanist investigating the origins and nature of consciousness. He approaches complex scientific theories and philosophical debates with curiosity, positioning himself as an active participant rather than a detached observer. His background in literature and previous experiences with psychedelics heavily inform his perspective as he questions the strict boundaries of physical science.

Christof is a German American neuroscientist who enters the field as an MIT postdoc in the late 1980s. He initially operates as a staunch materialist, firmly believing that consciousness can be entirely mapped to the physical matter of the brain. He represents the optimistic peak of hard science's attempt to decode subjective experience through neurology.

David is an Australian-born philosopher famous for distinguishing the "easy problems" of neurological mapping from the "hard problem" of subjective experience. Rather than proposing his own comprehensive theories, he functions as an analytical critic who tests the limits of other researchers' ideas. He maintains deep skepticism toward any claim that physical science has fully explained inner feeling.

Stefano is an Italian plant scientist at the University of Florence who directs the International Laboratory of Plant Neurobiology. He conducts maze experiments with corn roots and catalogs the thousands of chemicals plants use to interact with their environment. He argues that brains and neurons are not prerequisites for intelligence or basic sentience.

Michael is an American developmental biologist at Tufts University who creates "Xenobots"—synthetic proto-organisms made from frog skin cells. He argues that bioelectricity, rather than strictly DNA or neurons, is the essential software of living organisms. As a gradualist, he views consciousness as a spectrum that begins with basic homeostasis, comparing early sentience to the functions of a thermostat.

Karl is a physicist, neuroscientist, and psychiatrist at University College London. He develops the theoretical frameworks behind brain imaging tools and formulates the "free-energy principle." He argues that the fundamental goal of all complex systems is to resist entropy and minimize surprise, viewing this drive for homeostasis as the bedrock of consciousness.

Antonio is a Portuguese biologist and neuroscientist who emphasizes the biological necessity of emotion. He argues that feelings evolved in the brainstem to help organisms monitor internal survival needs, making the physical body a non-negotiable requirement for true consciousness. He rejects the idea that a disembodied computer program could ever experience authentic sentience.

Russell is an American psychologist at the University of Nevada, Las Vegas, who utilizes the Descriptive Experience Sampling method. He designs a specialized beeper to prompt subjects to record their immediate inner experiences at random intervals. He is highly rigorous in his methodology, insisting that true thoughts must be separated from their post-facto contexts.

Kalina is a Bulgarian-born psychologist and jazz pianist who uses brain scanners to study daydreaming and mental wandering. She argues that thoughts originate in the unconscious long before they register in active awareness. She criticizes the scientific community's bias toward structured, goal-oriented thinking, which she attributes to capitalist pressures.

Joan is a Buddhist monk, abbot of the Upaya Zen Center, and director of a mountain healthcare clinic. Instead of offering purely academic answers about consciousness, she directs her visitors toward experiential learning. She teaches that intense, repetitive meditation can break down the ego and temporarily dissolve the illusion of an individual self.

Mark is a neuroscientist and psychoanalyst who works with a team of roboticists to construct a conscious artificial intelligence. He theorizes that programming a machine to experience uncertainty and seek homeostasis will eventually cause it to develop genuine, subjective feelings.

Anil is a neuroscientist known for describing human perception as a "controlled hallucination." He argues that the brain functions primarily as a prediction machine, constantly guessing the causes of sensory input, and that the feeling of having an individual self is simply another one of these biological inferences.

Kingson is a researcher investigating how to give artificial intelligence the functional equivalent of feeling by housing it in damageable bodies. Following a profound psychedelic experience, he expresses doubt to Michael Pollan that human consciousness can ever be completely replicated by engineered machines.

Francis is a Nobel Prize-winning scientist who co-discovered the structure of DNA. In the 1980s and 90s, he spearheads early efforts to locate the specific neural correlates of consciousness, operating under the assumption that science will neatly reduce the mind to physical biology.

Blake is a Google engineer who is fired after publicly asserting that an artificial intelligence program has achieved sentience. He maintains a firm belief that the machine possesses genuine understanding, sparking broader debates about the nature of artificial thought.

Matthieu is a French scientist who leaves his academic career to become a Buddhist monk. He instructs Michael Pollan in visualization exercises designed to demonstrate that the individual self is an illusion, arguing that this realization is the key to escaping defensiveness and suffering.

Alison is a developmental psychologist and philosopher of mind who studies consciousness in young children. She explains that babies operate with a wide, awe-inspiring "lantern consciousness" and notes that a true, continuous sense of self does not form until children develop episodic memory around age four.