PAIN AND PLEASURE 261 



sociate pains, referred pains), and almost invariably of motor centers of 

 visceral, facial, and other muscles of expression (emotional discharge)." 

 Our own view is in harmony with that expressed in this paragraph except 

 that, while we recognize that sensations in general have an affective tone, 

 we do not consider that affective experience is to be regarded as essentially 

 an attribute or quale of sensation. These are independent variables which 

 are, however, usually intimately associated. Each has its own mechanism. 

 The mechanism of every sensation is a localizable system of tracts and 

 centers as expounded in the preceding chapters. The mechanism of the 

 affective experience is a more general neural attitude or physiological phase, 

 intimately bound up with the visceral reactions peripherally and inte- 

 grated centrally in the thalamus. 



Summary. In the human organism pain appears to be a true 

 sensation with its own receptors, probably with independent 

 peripheral neurons (in some cases at least), and certainly with 

 well localized conduction paths and cerebral centers, these cen- 

 ters being thalamic and not cortical. Pain appears to be closely 

 related neurologically with feelings of unpleasantness and pleas- 

 antness, and these, in turn, with the higher emotions and the 

 affective life in general. The intellectual elements in the higher 

 emotions and sentiments are, of course, cortical, and in nearly all 

 cases the affective experience probably involves a highly complex 

 interaction of cortical and subcortical activities. Pleasantness 

 and unpleasantness are not regarded simply as attributes of 

 specific sensory processes in any case, but rather as a mode of 

 reaction or physiological attitude of the whole nervous system 

 intimately bound up with certain visceral reactions of a protec- 

 tive sort whose central control is effected in the ventral and medial 

 parts of the thalamus. These parts of the thalamus form, ac- 

 cordingly, the chief integrating center of the nervous reactions 

 involved in purely affective experience. This mechanism is 

 phylogenetically very old, and in lower vertebrates which lack 

 the cerebral cortex it is adequate to direct avoiding reactions to 

 noxious stimuli and seeking reactions to beneficial stimuli. 

 With the appearance of the cortex in vertebrate evolution these 

 thalamic centers became intimately connected with the associ- 

 ation centers of the cerebral hemispheres, and an intelligent 

 analysis of the feelings of unpleasantness and pleasantness be- 

 came possible. As a final step in the development of the pro- 

 tective apparatus the peripheral nerves of painful sensibility, 

 with their own specific conduction paths and centers, were differ- 



