Every animal sleeps, but the reason for this has remained foggy. When lab rats are not allowed to sleep,t hey die within amonth. ①
One idea is that sleep helps us strengthen new memories. ② We know that, while awake, fresh memories are recorded by reinforeing (加强) connections between brain cells,but the memory processes that take place while we sleep have been unclear.
Support is growing for a theory that sleep evolved so that connections between neurons (神经元) in the brain can be weakened overnight,making room for fresh memories to from the next day. ③
