[Centenary of I.P. Pavlov's Madrid speech (April, 1903): Subjective aspect of mental activity as an object of system analysis].

The main pathstones of methodological approaches to objective exploration of mental activity outlined by I.P. Pavlov in 1903, in particular, such its features as the ability to forsee the results, expediency, reasonable character, and adaptivity of behavior are considered. Stages of methodological perfection of investigations of the inner (mental) states of living organisms, semantic transformation of conditioned reflex, conditioning of the first and second orders, systems of conditioned reflexes, psychonervous activity, causal and extrapolative reflexes are analyzed. The significance of the development of the theory of the functional system by P.K. Anokhin and the modern state of its understanding are shown. The functional significance and neurophysiologic mechanisms of movement task, programming, motivation, memory engram, reinforcement etc. is discussed.