The Twenty-Four Hour Mind: The Role of Sleep and Dreaming in Our Emotional Lives
by Rosalind Cartwright. Oxford University Press, 2010

Less than six hours of nightly sleep can lead to obesity and even death, but sleep plays an equally important role in regulating our emotions. In The Twenty-Four Hour Mind psychologist Rosalind Cartwright gives an engaging account of the history of sleep research. She skillfully weaves in her 50 years’ worth of work in the field, delving into her own theories about the purpose of dreams and highlighting the importance of sleep to maintain our physical and mental well-being.

Cartwright proposes that dreams diffuse the impact of otherwise disturbing emotions by matching them with similar experiences already stored in our long-term memory. Her own studies have shown that even when people go to bed angry or sad, their dreams can turn progressively more positive as the night wears on, allowing the person to wake up in a better mood. She has also built her theory on studies in which volunteers played virtual games and later associated the emotional situations in the games to experiences in their own lives. While they slept, volunteers reported pairing the virtual images with memories of similar emotional experiences. Cartwright concluded that this emotional matching process mitigates some of the negative feelings associated with the events.

Cartwright describes why comparing these emotional experiences gives us some strange nightly adventures. For instance, you may be dreaming about your boyfriend, and he suddenly morphs into your uncle who recently left his wife. According to several studies, each consecutive 90- to 110-minute sleep cycle integrates more and more associations from your memory, stretching the story line “into increasingly illogical and bizarre connections.” By the time you wake up, your dream has turned into complete nonsense. Cartwright’s hypothesis, though compelling, is just one theory—sleep researchers are far from agreeing on the origin and purpose of dreams.

Sleep disorders can disrupt a person’s emotional maintenance system, a predicament that Cartwright demonstrates vividly through detailed accounts of sleepwalking violence cases. Studies are also now beginning to show that continuous loss of sleep could be an underlying cause of depression, “affecting how we think, feel, define ourselves and relate to others,” Cartwright says. The Twenty-Four Hour Mind brings home the importance of the brain’s
“essential night-shift.”

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