Sentence:  As retinal images are conceded to be an integral function of the brain it seems logical to suppose that the nerves , between the inner brain and the eyes , carry the direct <WSD>drive</WSD> for cooperation from the various brain centers - rather than to theorize on the transmission of an image which is already in required location . 
Meaning of the word marked with <WSD> tags:  a series of actions advancing a principle or tending toward a particular end