If there is anything in the world that can really be called a man's property, it is surely that which is the result of his mental activity. Arthur Schopenhauer
The operations of the human mind are also controlled by words of power, formulas that become a focus of mental activity. Northrop Frye
What people call impartiality may simply mean indifference, and what people call partiality may simply mean mental activity. G. K. Chesterton
I'm struck by the insidious, computer-driven tendency to take things out of the domain of muscular activity and put them into the domain of mental activity. Brian Eno
It defaces every type of mental activity - history, art, politics, science and social reform. Jacques Barzun
By relaxation, I don't mean falling asleep in front of the TV set or unwinding with friends. The kind I'm talking about is a quieting of mental activity and withdrawal of body and mind from external stimulation. Bernie Siegel