When I saw the trailer for Lucy, a new thriller starring a superhuman Scarlett Johansson, my first thought was: Yes! Hollywood finally cast a black actor as a neuroscientist! And my second thought was bummer, because that neuroscientist, played by Morgan Freeman, immediately discredits himself: “It is estimated most human beings only use 10 percent of the brain’s capacity,” he says. “Imagine if we could access 100 percent.”

Luckily, we don’t have to imagine. Unless you have a traumatic brain injury or other neurological disorder, you already have access to 100 percent of your brain! Your brain is available all the time, even when you’re sleeping. Even the most basic functions of your brain use more than 10 percent—your hindbrain and cerebellum, which control automatic bodily functions like breathing and balance, make up 12 percent of your brain, and you definitely need those just to stay alive.

Basic biology also tells us that it’s unlikely we’re leaving 90 percent of the brain unused. Unused cells tend to atrophy; for instance, muscle atrophy occurs in people who have a broken arm in a sling for several weeks. Parts of the brain we aren’t using would also atrophy—and this is actually what happens when our brains are deprived of blood flow or oxygen, as happens during a stroke or heart attack. Remember Terri Schiavo? She was in a vegetative state for 15 years after she went into cardiac arrest, which damaged 50 percent of her brain. Even damage to small, specific portions of the brain can drastically affect day-to-day functioning, leaving people unable to talk, read, or understand language. Losing 90 percent of your brain would be catastrophic and almost certainly fatal.

Well, maybe Dr. Freeman meant something else? There is a way to measure what parts of the brain are actively working. Neuroscientists often measure brain activity by identifying the places in which brain cells, called neurons, are sending chemical and electrical signals to other neurons. Perhaps what Freeman’s neuroscientist character meant was that only 10 percent of our neurons are firing at any given time. But this interpretation doesn’t fare much better: By any measure of brain activity, more than 10 percent is being used, and in any case, you don’t want 100 percent of your neurons firing at once, because that would constitute a killer seizure.

Another major premise of Lucy is that if we were able to use more than 10 percent of the brain, we could unlock “secrets of the universe.” Judging from the trailer, this apparently includes stopping time, making people around you fall down, and spontaneously changing your own hair and eye color. This probably doesn’t bear explaining, but just in case you were wondering: Sadly, your individual brain cannot control space-time, others’ actions, or the expression of your genes. We’ll have to wait for some other type of fictional drug to turn us into crime-fighting mutants.