In this episode of the podcast, Sam Harris speaks with Matthew Walker about the nature and importance of sleep. They discuss sleep and consciousness, the stages of sleep, sleep regularity, light and temperature, the evolutionary origins of sleep, reducing sleep, the connection between poor sleep and all-cause mortality (as well as Alzheimer’s disease, diabetes, obesity, and heart disease), sleep across species, learning and memory, mental health, dreams as therapy, lucid dreaming, heart-rate variability, REM-sleep behavior disorder and parasomnias, meditation and sleep, sleep hygiene, different types of insomnia, caffeine and alcohol, sleep efficiency, bedtime restriction, cognitive-behavioral therapy, napping, sleep tracking, and other topics. SUBSCRIBE to listen to the rest of this episode and gain access to all full-length episodes of the podcast at samharris.org/subscribe.   Learning how to train your mind is the single greatest investment you can make in life. That’s why Sam Harris created the Waking Up app. From rational mindfulness practice to lessons on some of life’s most important topics, join Sam as he demystifies the practice of meditation and explores the theory behind it.