Reflex Prepotency

From our present point of view, the fourth determinant of the issue of a conflict, as listed by Sherrington, is probably the most interesting of all. It consists in the species or kind of reflex which is involved. Certain classes of reflexes exhibit very superior strength when they come into conflict with reflexes belonging to a different class. Among such very potent--or "prepotent"--reflexes are those which are aroused by stimulation of nociceptive sense-organs. These are receptors, or senseorgans which respond specifically to injurious stimuli, their most important exemplars being the receptors of the pain sense. It is natural that the reflexes which are set off by pain stimulation should dominate over those which are aroused by innocuous stimuli, such as mere contact, since an appropriate reaction to the former is of vital importance to the welfare of the organism. The dominance of the flexion over the scratch reflex, which we have already mentioned above, is explained by this principle of the prepotency of nociceptively aroused reactions, since the flexion reflex is a response to a needle prick, whereas the scratch reflex follows from a harmless touch. However, if the pain stimulus is sufficiently weak and the tactile one sufficiently strong, the scratching action may appear, and become dominant over the continuous flexion process. Nociceptive reflexes show a tendency to persist in the face of general disturbances of nervous activity which obliterate many other reflex processes, thus showing the peculiar vitality of the former types of response.

Sherrington points out, furthermore, that any reflex arising from the stimulation of receptors which can produce strongly pleasant or unpleasant (affective) consequences in consciousness, tends to prevail over other types of reflexes in the case of conflict. He calls such reflexes in general "pseudaffective." The sexual reflexes, such as the embracing reaction in the case of the male frog during the breeding season, show a prepotency as great as, or greater than that which is exhibited by nociceptive reflexes. In order to complete our terminology, it seems advisable to invent the adjective, beneceptive, to designate sensory processes and attached reflexes which are of the character of the sexual responses, as contrasted with those of pain. Nociceptors may be defined as sensory cells, or afferent mechanisms, which are particularly attuned to injurious agencies; whereas beneceptors may be considered as similarly qualified with respect to especially beneficial environmental, or organic, conditions. We can then say that reflexes which are aroused by the stimulation of either nociceptors or beneceptors tend, other things being equal, to dominate over the motor tendencies appertaining to other forms of sensory excitation.

All of the factors which control the outcome of conflicts between reflex arcs apparently can be interpreted as different grounds of response intensity, presumably in the adjustor stage of the reflex. This applies not only to the influence of spinal induction, fatigue, and stimulus magnitude, but also to the species of reflexes, since it seems highly probable that the nociceptively and beneceptively aroused adjustor processes have a high degree of nervous power. This is evidenced by the fact that their normal, unimpeded expressions show great strength and persistence. The conflict of response tendencies is therefore fundamentally a quantitative affair, in which the result is dependent upon the comparative magnitudes of the positive and negative forces which are operative. For it seems that each response tendency must be capable of acting both positively and negatively: positively in seeking its own expression, and negatively in opposing the expression of its antagonists.