The Physiology of Pain

Abstract

Pain has been defined by Sherrington ¹⁰⁷ as “the psychical adjunct of an imperative protective reflex.” In this definition it will be noted that the protective reflex is the primary response to harmful stimuli, and that pain is the “adjunct” or the added signal in consciousness accompanying the reflex. This concept is in conformity with the generally accepted view of the evolution of protective mechanisms, in which the reflexes are held to represent the most primitive protective reaction, appearing in the scale of evolution long before any such specific sensation as pain has evolved from the more primitive affective states. Herrick⁵¹ writes: “Our own view is that pleasurable and unpleasant experiences are not true sensations, that in the history of the psycho-genesis of primitive animals a diffuse, unlocalized affective experience of well-being or malaise probably antedated anything so clearly analyzed as the sensation with specific references, and that, parallel with the differentiation of true sensations of touch, temperature and so on in consciousness, pain sensations emerged out of the diffuse affective experience, and took their place among other qualities.”