A car accident. Your spinal cord is damaged, and communication between your brain and your legs is cut off. You're paralyzed. Permanently...? What if we could read your brain when you want to walk? Then we could send electrical stimuli to the spinal cord - underneath the lesion - to make your legs move again, and you could walk again! This is not science fiction, but a fast-growing field of research: brain-machine interfaces. Each of our thoughts corresponds to the activation of a combination of neurons. An artificial intelligence, connected to electrical cables implanted in the brain, can decode these thoughts to control a prosthesis. Such artificial intelligences can already tell whether you want to move your arm or leg, predict whether you're about to have an epileptic seizure, and even... guess whether you're happy or unhappy! How far will brain-machine interfaces go?

Neurofeedback and transcranial stimulation are neurotechnologies developed to treat illnesses. Today, however, they are sold for just a few hundred francs on the Internet and promise to increase your cognitive abilities. What are the ethical issues involved in consumer neurotechnologies?