‘How is the brain activated in sleep?’ explains the discovery of brain activation of sleep and how it changed the strategy from dream content to dream form. Adolf Berger's electroencephalograph (EEG) revolutionised sleep and dream science in 1928 as it provided an objective tool for assessing dynamic brain activity. The combination of EEG and electro-oculogram (EOG), which measure eye movement, enabled Eugene Aserinsky and Nathaniel Kleitman to make their 1953 discovery of brain activation in sleep. They called the brain activation phase of sleep REM (for rapid eye movements) because of the association of the activation of the eye movements with activation of the brain. They asserted that dreaming might be another associated event.