Charles Whitman (1944-1966) was a former Marine who, in 1966, murdered his wife and mother before killing 14 people and wounding dozens more in a mass shooting at the University of Texas. He was shot dead by police at the scene. Prior to the massacre, Whitman was known as a friendly and rational young man. In a note written before his crimes, he documented his struggle with overwhelming, irrational violent urges and asked for an autopsy, suspecting a physical cause for his mental change. When the autopsy on Whitman was conducted, it revealed a brain tumor pressing on his amygdala, a region important for regulating emotion and aggression.

For Eagleman, this discovery questions Whitman’s culpability. He argues that the tumor fundamentally altered his capacity for self-control, demonstrating how a change in neural hardware can produce a complete change in a person. Eagleman concludes that Whitman’s identity was hijacked by his biology: “His brain matter had been changing, and who he was changed with it” (21). Eagleman uses Whitman as a case study to show the deterministic properties of the physical brain and to introduce his discussion around personal choice, responsibility, and intersections with criminal justice.

Mike May (b. 1953) is used as a case study by Eagleman. May lost his sight in a chemical explosion at age three, but after 40 years of blindness, he chose to have his vision surgically restored. After having his bandages removed, May saw a confusing “whoosh of light and bombarding of images” (44) that he could not interpret. His eyes were functional but his brain, deprived of visual input for decades, had never learned how to see.

Eagleman features May’s story to dismantle the intuitive idea that our senses provide a direct and objective window onto reality. journey to make sense of visual information is central to Eagleman’s argument that reality is a neurological construction: He details how May had to consciously learn to distinguish faces, perceive depth, and identify objects his other senses knew intimately. May’s experience is used in the book as proof that sensory data is meaningless until the brain learns to interpret it through experience.

Ian Waterman (b. 1952) is used by Eagleman as a key case study. At age 19, Waterman lost his sense of proprioception—the unconscious awareness of his body’s position in space—due to a rare neurological illness. This means Waterman cannot move automatically: To walk or stand, he must use intense conscious concentration and visual focus to direct every single movement. He notes that if his concentration lapses for even a moment, he is “likely to fall” (84).

Eagleman presents Waterman’s case to reveal the vast, invisible work performed by the brain’s unconscious systems. Waterman’s condition makes the brain’s hidden autopilot visible. He details the immense mental effort Waterton must expend on simple actions to highlight the unconscious processes that allow most people to move without a second thought. Eagleman uses Waterman’s story to demonstrate that humans’ ability to perform complex skills effortlessly depends on trillions of neural calculations running smoothly in the background.

Jan Scheuermann (b. 1959) is used by Eagleman as a case study. Paralyzed from the neck down by a degenerative genetic disorder, Scheuermann engaged in a research study to have electrodes implanted in her motor cortex to read her brain’s signals for intended movements. A computer translated these signals into commands for a sophisticated robotic arm. Despite not having moved her own limbs for over a decade, Scheuermann was able to control the prosthesis with her thoughts, allowing her to perform tasks like eating and high-fiving researchers.

Eagleman features her in the book’s final chapter as a symbol of the brain’s extraordinary plasticity and humanity’s potential to transcend biological limitations through technology. He uses Scheuermann’s success as the foundation of his idea that the brain is a flexible, “plug-and-play” device capable of learning to control non-biological outputs. Eagleman presents Scheuermann as a pioneer in a new bionic era where the brain’s adaptability can be harnessed to repair, replace, and even enhance human capabilities. Her story is optimistic, reflecting the final chapter’s positive hypotheses for the future.