New research shows you’re unlikely to dream when it’s either too hot or too cold. That’s because your brain will focus all its energies on its primordial role — keeping you alive.
Swiss scientists studying the brains of genetically engineered mice were able to watch how changes in temperature affected the sleep state of these animals. What they found is the brain prioritizes temperature control over dreaming, especially in severe hot or cold.
Dreaming also suppresses temperature regulation or thermoregulation, which keeps our bodies at the right temperature for continuing to sleep. Our body normally reacts to heat and cold by sweating, shivering, panting and flushing.
These defense mechanisms, however, can’t maintain our core temperature once REM (rapid eye movement) sleep starts, because REM sleep places a lot of physical demands on the human body. The brain of a person in REM sleep, which can account for up to 25 percent of an adult’s sleep cycle, eats up almost as much energy as when it’s awake.
Also during REM sleep, your breathing can increase, your eyes keep moving to track imagined characters, and your arms and feet twitch as they fight against the urge to move and wake you. All these activities drain you of energy when you’re asleep and combine to create an energy-depleting mental workout.
If you add a sleep environment that’s either too hot or too cold, your brain will compensate for this additional stress by refusing to let you dream so you can conserve enough energy to stay alive.
Faced with this scenario, our brain makes a choice. It either lets you dream or refuses to let you dream in favor of keeping your body from freezing or frying.