Motivation is considered as a key component of systemic organization of mental activity. Forming on the stage of afferent synthesis, motivation determines activity of the subsequent systemic architectonic stages of mental acts: decision-making, construction of an acceptor of resulting actions, efferent synthesis and the very purposeful action. It is shown that motivation acts as an energy basis of mental activity. The foresight instrument of required resulting actions--an acceptor of resulting actions that, strongly linked to dominating motivation, is a leading guiding component of mental actions. A role of motivation in the processes of perception, memory, movement organization, intellectual and creative activity and their relationship to emotions are considered. A conception of motivation as a basis of intellect is formulated.