I've been up for a considerable amount of time, and my brother is sleeping in the room my computer is located at. Through the course of the night, I've witnessed my brother talking alot in his sleep. He says things like "No, Why, Come On..." and so on periodically. Why is it that some people tend to say things aloud as they sleep? Does a specific thing cause it?

Interestingly, the only thing I have heard people speak in their sleep were also "No" and "Don't".

Does a specific thing cause it?

Stress perhaps? Maybe the frontal lobe isn't completely paralyzed during dreaming so some muscle movement is allowed in the form of talking out loud when dreaming?
:bugeye:

I often talk in my sleep when im really exausted or had a really unusual day. I'll usually start talking a few minutes after i've gone to sleep. One night after I went to sleep I nudged my girlfriend and said "my arm....." She asked what I was talking about and I told her "it can hold fifteen sandwhiches..."

I don't think anyone really knows why people talk in their sleep, but i think its something that everyone does, just some people do more than others.