Ask the Brains; February/March 2008; Scientific American Mind; by Antonio Oliviero, Mark A. W. Andrews; 1 Page(s)

Sleep disorders such as sleepwalking arise when normal physiological systems are active at inappropriate times. We do not yet understand why the brain issues commands to the muscles during certain phases of sleep, but we do know that these commands are usually suppressed by other neurological mechanisms. At times this suppression can be incomplete--because of genetic or environmental factors or physical immaturity--and actions that normally occur during wakefulness emerge in sleep.

People can perform a variety of activities while asleep, from simply sitting up in bed to more complex behavior such as housecleaning or driving a car. Individuals in this trancelike state are difficult to rouse, and if awoken they are often confused and unaware of the events that have taken place. Sleepwalking most often occurs during childhood, perhaps because children spend more time in the "deep sleep" phase of slumber. Physical activity only happens during the non-rapid eye movement (NREM) cycle of deep sleep, which precedes the dreaming state of REM sleep.