Dreams have fascinated people for thousands of years, yet we struggle to understand their purpose. A more recent theory suggests nighttime dreams protect visual areas of the brain from being taken over during sleep by other sensory functions, such as hearing or touch.
David Eagle-man, a neuroscience at Stanford University, has proposed the idea that dreaming is necessary to protect the visual cortex (大脑皮层)—the part of the brain responsible for processing vision. He argues that neurons (神经元) compete for survival. The brain, Eagle-man explains, distributes its resources by “implementing a do-or-die competition” for brain territory in which sensory areas “gain or lose neural territory when inputs slow, stop or shift.” Eagle-man points to people who lose sight or hearing. They show heightened sensitivity in the remaining senses because the region of the brain normally used by the lost sense is taken over by other senses.
When you sleep, you can smell, hear and feel, but visual information is absent —except during REM sleep. About 90 minutes after drifting off to sleep, you enter REM. It begins when neurons in your brain stem signal the beginning of two important tasks. Activity of these neurons, for one, paralyze major muscles, preventing the sleeper from acting out what is happening in the dream. Also, these brain cells send messages directly to the visual cortex, which starts the dreaming process. Scans of dreaming people show most of the brain activity associated with REM is within the visual cortex. Dreams are the brain’s way of fighting takeover from other senses, according to Eagle-man.
Eagle-man says that his theory can accommodate other explanations for dreams and that REM sleep may serve many purposes besides protecting the visual cortex. Think of dreaming like a computer screen saver that is set to go off every 90 minutes —except that instead of protecting against frozen images, dreams prevent the visual cortex from being occupied by other functions.
【小题1】What is Eagle-man’s primary theory about dreams?| A．They strengthen sensory functions. | B．They process emotional experiences. |
| C．They safeguard certain brain territory. | D．They heighten visual responsiveness. |
| A．Precise selection. | B．Desperate struggle. | C．Rapid adaptation. | D．Harmonious balance. |
| A．It lasts for about 90 minutes. | B．It consists of two critical stages. |
| C．It allows sleepers to act out their dreams. | D．It starts with brain stem’s signaling process. |
| A．To show their creative aspect. | B．To highlight their randomness. |
| C．To signify their repetitive nature. | D．To illustrate their protective function. |
