这个句子确实是用because从句作了主语。但这种句子是不规范的。如果你仔细分析句子的逻辑，你也会发现because从句作主语与谓语动词之间是难以构成主谓关系的。句子应该改为that从句作状语。例如：

That our brain is no longer processing the adenosine doesn't mean it stops producing it. 或者：

Although our brain is no longer processing the adenosine，it doesn't mean our brain stops producing it.

Our brain is no longer processing the adenosine, but it doesn't mean our brain stops producing it.