We human beings spend a third of our lives sleeping. Healthy sleep is essential for good health and productivity. However, there are fundamental questions that remain unanswered, such as: “Why do all animals sleep?” and “What exactly is sleepiness in the brain?” Dr. Yanagisawa says that sleep is one of the largest black boxes in neuroscience. He introduced cases that have been revealed with the progress of sleep research. He explained the adverse impact of sleep deprivation, including weakening of the amygdala’s control functions, which makes emotional control more difficult and increases the risk of dementia due to a rise in the accumulation of brain amyloid-β, believed to be one of the factors that causes Alzheimer’s disease. He also talked about the background to his research into orexin, whose role he discovered in sleep-wake regulation in 1998. He explained how orexin receptor antagonists used to treat insomnia disorders do not cause drug dependency or the apparent drunkenness observed with the use of conventional sleep drugs. In the final part of the lecture, he presented findings from InSomnograf, the home sleep electroencephalogram monitoring service he is currently promoting: 66% of people who felt they suffer from insomnia showed no objective detection of sleeplessness, while 45% of those who felt that they had sufficient sleep exactly lacked sleep. His comments that “personal awareness of the length and quality of sleep is often unreliable” brought surprised reactions from the audience.