The 20th century philosopher Ludwig Wittgenstein argued that the most important things in people’s lives are always hidden from them—people don’t think twice about their most basic sensations and ideas. Neurologists have found that people have a sixth sense in addition to the five familiar senses. This “sixth sense,” which scientists have termed “proprioception,” consists of the ability to feel one’s body as one’s own, and to feel a continuous flow between the body and the external world. Such a feeling is so basic that we take it for granted. One could say that Wittgenstein’s late philosophy is about what would happen if humans lost proprioception—if they had to question their most basic behaviors.
Sacks’s erudition is on full-display in this chapter: his knowledge encompasses philosophy, art, history, and literature in addition to neurology. Wittgenstein is considered one of the greatest philosophers of the twentieth century, and in this chapter, Sacks finds a surprising, real-world counterpart for one of Wittgenstein’s most challenging ideas—the idea of humans being uncertain of their own existence, or the existence of their own bodies.
Sacks describes a woman named Christina, who worked as a computer programmer. At the age of twenty-seven, she was hospitalized to have her gallbladder removed. The day before her surgery (while sleeping in the hospital), Christina had a nightmare in which she couldn’t stop her body from flailing around. The doctors assumed that Christina was feeling nervous about her surgery. On the day of the surgery, however, she reported anxiety, and told her doctors that she couldn’t feel her body.
The doctors interpret Christina’s nightmares and anxieties as manifestations of her fear of having surgery; however, retrospectively, it seems likely that these anxieties reflected the “last gasp” of her proprioceptive abilities.
Doctors brought in Oliver Sacks to examine Christina. He found that Christina had lost all proprioception—she could still use her five senses, but she couldn’t feel anything in her muscles or joints, meaning that she had no sense of familiarity with her body. Sacks informed Christina that she’d lost her proprioception, and Christina realized that, in order to compensate, she’d have to use her senses to regain a “sense” of her body. Instead of intuitively knowing where her arm was, for example, she’d have to use her vision to locate it.
From an early age, we’re taught that we perceive the world thanks to our five senses, but this clearly isn’t the full story. Humans wouldn’t “feel themselves” without proprioception. However, as Christina proves, it’s possible to adapt to one’s lack of proprioception by relying more heavily on the five senses.
In the following weeks, Sacks and his fellow doctors helped Christina regain her confidence while walking. Most people control their voices proprioceptively—they know how to modulate their tone and volume because of an intuitive understanding of their vocal organs. But Sacks noticed that Christina now had to rely on hearing to standardize her voice’s volume and tone. She also had to re-learn the most basic behaviors—talking, walking, eating. Christina could still feel superficial sensations, such as the feeling of the wind on her body and face. However, as in Wittgenstein’s writings, she was forced to doubt and question her sense of connection to her own body. Over the next few years, she learned how to work around proprioception, compensating with her senses—and yet, she remained a “disembodied” human being.
Although Sacks can’t cure Christina’s lack of proprioception, he can train her to “work around” her neurological impairment. Christina spends the rest of her life uncertain of her own body (or, at Wittgenstein might have put it, “doubting” her body). But she learns to use her five other senses to navigate her way through the world and live a fairly normal, happy life.
In the Postscript, Sacks mentions other patients who lost their proprioception. Many of these patients were health nuts and took large amounts of vitamin B6—perhaps they’ll regain their proprioception, Sacks says, after they stop “poisoning themselves.”
As Sacks somewhat sarcastically notes, some people have accidentally stripped themselves of their proprioception by taking the wrong vitamins.