"It is evident here that the physiological factors in the dilemma or problem as this is presented to the cortex are by no means simple sensory impressions, but definitely organized systems of neural discharge, each of which is a physiological resultant of the reflexes, automatisms, impulses, and inhibitions characteristic of its appropriate subcortical centers. The precise form which these subcortical combinations will assume in response to any particular excitation is in large measure determined by the structural connections _inter se_.... "From the standpoint of the cerebral cortex considered as an essential part of the mechanism of higher conscious acts, every afferent stimulus, as we have seen, is to some extent affected by its passage through various subcortical association centers (i.e., it carries a quale of central origin). But this same afferent impulse in its passage through the spinal cord and brain stem may, before reaching the cortex, discharge collateral impulses into the lower centers of reflex cooerdination, from which incipient (or even actually consummated) motor responses are discharged previous to the cortical reaction. These motor discharges may, through the 'back stroke' action, in turn exert an influence upon the slower cortical reaction. Thus the lower reflex response may in a literal physiological sense act _into_ the cortical stimulus complex and become an integral part of it."[37] It seems clear, then, that conscious behavior involves a certain _process_ of organization which constitutes a differential. The units entering into this process are "definitely organized systems of neural discharge," the antecedent organization of these several systems being due either to the inherited or to the acquired structure of the nervous system. Given a certain amount of plasticity, the nervous system builds up specific forms of response for certain objects or situations, and these forms of response subsequently become the material from which new organizations or new modes of response are constructed. The achievements of the past, accordingly, become stepping-stones to new achievement. The new organization, moreover, is not determined by a mechanism antecedently provided, but has a peculiar flexibility, so as to meet the demands of a new situation. That is, a new mode of procedure is adopted. Instead of being a purely mechanical reaction, the response that results from the situation is tentative or experimental in character, and "by a process of trial and error, perhaps, the elements necessary to effect the adaptive response may be assembled and the problem solved."