Neuroscientists' New Theory: Dreaming Protects the Braincells For Eyesight

Writing in Time magazine, two neuroscientists share a surprising new theory on exactly how dreaming protects our brains: Neuroscience used to think that different parts of the brain were predetermined to perform specific functions. But more recent discoveries have upended the old paradigm. One part of the brain may initially be assigned a specific task; for instance, the back of our brain is called the "visual cortex" because it usually handles sight. But that territory can be reassigned to a different task... Recent decades have yielded several revelations about livewiring, but perhaps the biggest surprise is its rapidity... In the ceaseless competition for brain territory, the visual system has a unique problem: due to the planet's rotation, all animals are cast into darkness for an average of 12 out of every 24 hours... So how did the visual cortex of our ancestors' brains defend its territory, in the absence of input from the eyes? We suggest that the brain preserves the territory of the visual cortex by keeping it active at night. In our "defensive activation theory," dream sleep exists to keep neurons in the visual cortex active, thereby combating a takeover by the neighboring senses. In this view, dreams are primarily visual precisely because this is the only sense that is disadvantaged by darkness. Thus, only the visual cortex is vulnerable in a way that warrants internally-generated activity to preserve its territory... REM sleep is triggered by a specialized set of neurons that pump activity straight into the brain's visual cortex, causing us to experience vision even though our eyes are closed... The anatomical precision of these circuits suggests that dream sleep is biologically important — such precise and universal circuitry rarely evolves without an important function behind it... We suggest that dream sleep exists, at least in part, to prevent the other senses from taking over the brain's visual cortex when it goes unused. Dreams are the counterbalance against too much flexibility. Thus, although dreams have long been the subject of song and story, they may be better understood as the strange lovechild of brain plasticity and the rotation of the planet.

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