line of thought vs mentation

line of thought and mentation both are nouns.

Word	Noun	Adjective	Verb	Adverb
line of thought	Yes	No	No	No
mentation	Yes	No	No	No

As nouns, mentation is a hypernym of line of thought; that is, mentation is a word with a broader meaning than line of thought:

line of thought: a particular way of thinking that is characteristic of some individual or group
mentation: the process of using your mind to consider something carefully

Other hypernyms of line of thought include cerebration, intellection, thinking, thought, thought process.

line of thought (noun)	mentation (noun)
a particular way of thinking that is characteristic of some individual or group	the process of using your mind to consider something carefully