Who said "The mind must be exercised like a muscle."?

This quote is attributed to Dexter.

The mind must be exercised like a muscle. - Dexter

"The mind must be exercised like a muscle."

Dexter Strength

"What does this button do?"

"I must focus on my work."

"Science rules!"

"Dee Dee, get out of my laboratory!"

"Strength comes from within."

"A woman should be proud of who she is."

"A strong woman can overcome anything."

"The only thing I'm good at is killing."