17. And one leading authority says that these intensely powerful mental events can be not only harnessed but actually brought under conscious control, to help us sleep and feel better.

【分析】復合句。句子主干為one leading authority says that…，that引導賓語從句，其主干為these…mental events can be not only harnessed but... brought under conscious control。其中 not only...but...表示“不僅…而且...”;句末的不定式短語作目的狀語。
【譯文】一名主要的權威人士說，夢這種異常強烈的精神活動不僅能被駕馭，事實上還可以有意識的加以控制，以幫助我們睡眠更好，感覺更佳。

18. But not all parts of the brain are equally involved;the limbic system (the "emotional brain"）is especially active, while the prefrontal cortex (the center of intellect and reasoning) is relatively quiet.

【分析】并列句。分號連接兩個并列的分句，后一分是對前一分句的解釋說明，其中又包含由while連接的兩個并列分句，表對比關系。
【譯文】但并非大腦所有部分的活動都是均等的，腦邊緣系統(“情緒大腦”）尤其活躍，而前額皮質（思維和推理的中心部位）則相對安靜。