Movement of the human body was the first that must have existed. All other functions were developed from the movement. When we talk about movement, we have to talk about differential equations. Differential equations describe all types of movement. We are not able to describe complex movements using mathematical expressions.
Many books explain the function of the brain starting other functions.
However these functions are mostly higher function that the brain must process. Therefore it is difficult to find function of the human brain. If we start to describe function if the human brain using differential equations, we have to show how the human brain can solve integration of the differential equations. The integration operation is the basic rule for solution to the differential equations. Main problem of the integration in the brain is in the structure of the brain.