Is it true that people cannot sneeze while they're asleep?!

Is it true that people cannot sneeze while they're asleep?

It seems to be true, in my experiences. But why is that? Isn't a sneeze a reaction to a tickle in the nose? Then why wouldn't someone be tickled in their nose while asleep?

Well the fact is that humans cannot sneeze while asleep.
Sneezing requires a reflex mechanism, wherein the sensory nerves in our upper respiratory tract, esp nostrils, are stimulated by some stimuli (mechanical or chemical or other) and these nerves then go to the CNS (i.e brain) and as a final process excite the nerves which supply muscles of our respiration and the pharngeal region and the person sneezes thus. You must know that this reflex is a natural means to protect our sensitive upper respiratory tract from harmful influences or, more appropriately, external influences, be it a solid or a gas or as a response to some infection. Now when the person sleeps, the brain is not working at its normal levels and so even though the person's nerves have some external factor acting upon them, no reflex is initiated and the person doesn't sneeze. You must also know that when the stimuli continues or crosses a particular level, it changes from an irritative agent to a source of maybe say pain and then the person can have a disturbed sleep; there is a threshold for every thing.