As an example, consider a dream in which you are being chased but feel that you cannot run away. According to the activation - synthesis theory, this might reflect the forebrain's attempt to explain the failure of signals from the motor areas of the brain to stimulate limb movements during the paralysis that accompanies REM sleep paralysis produce by activity in the brainstem. During REM sleep, the pons generates neural impulses that activate the random regions of the cerebral cortex that controls leg and arms movements. Because your limbs are paralyzed during REM sleep, you might synthesize the cortical arousal and limb paralysis into a dream about running in place without being able to move or stop.