Mentation is a noun that refers to mental activity.

Mens (MENS) is the Latin word for minds. It has given English such related words as ‘mental,’ ‘mentality,’ and our word of the day, mentation which may refer to any kind of behavior performed by the brain.

Discovering who ate the cookies didn’t require any mentation on my part. I only had to trace the crumbs to Oscar’s food dish. The only calculations needed involved finding out how he did it without anyone seeing him.