Halfway into my first marathon, a nagging ache begins to seep from my feet into my ankles. “The wheels are falling off the bus,” I yell as I pass my husband on the sidelines. I’m half-joking, but by the time I hit mile 20, the ache becomes a searing pain. Each time my sneakers strike the trail, the blisters on my toes threaten to rupture. I am in agony. The sound of Billy Joel blasting through my earphones isn’t loud enough to drown out the inner voice that says, “You can’t do this. You’ve failed.” My jog slows to a trot, and soon, I’m hobbling.
After the race, I start to wonder whether it was my body or my mind that gave up first. Could I have kept running if the voice had shut up? And what is this voice, anyway? Where does it come from, and why do we have it?
In search of answers, I begin combing through the scientific literature. One man’s name appears again and again: Lev Vygotsky, a Russian psychologist. He proposed in the 1930s that our inner voice evolves when we are still children. We first learn to use speech to communicate with others. Soon, we begin to speak to ourselves, too. We’ve all heard children talk to themselves as they build Lego battleships or whip up imaginary pancakes. Eventually, Vygotsky wrote, those private conversations begin to take place silently inside our heads.
Many people still subscribe to this theory, I discover, including Charles Fernyhough, a psychologist at Durham University in Britain who studies the relationship between inner speech and voice hearing. “Inner speech is just private speech that has been fully internalized,” he tells me. “The stuff that you do in your head as you’re running the marathon is basically a version of the stuff you used to do out loud as a kid.”
