296 INTRODUCTION TO NEUROLOGY 



tract leading to neuron system number two (the auditory com- 

 plex established last year when the song was heard) has a lowered 

 physiological resistance by virtue of the previous collocation 

 with system number one, and I remember the song (see p. 64) . 

 It should be emphasized that the mechanism of association 

 here suggested is purely theoretical; we have no scientific evi- 

 dence regarding the details of such physiological processes. But 

 it can be confidently asserted that even the simplest associational 

 processes are at least as complex as this, and may involve the 

 participation of thousands of neurons in widely separate parts of 

 the cortex; and the consciousness must be regarded as a function 

 of the entire process, not of any detached center (cf. p. 66). 



In summarizing this dynamic conception of the nature of consciousness I 

 will quote a few sentences from my brother's writings (see C. L. Herrick, 

 1910, pp. 13, 14): 



"The theory of consciousness which seems best to conform to the condi- 

 tions of brain structure and its observed unity is that each conscious state is 

 an expression of the total equilibrium of the conscious mechanism, and that 

 intercurrent stimuli are continually shifting the equilibrium from one to 

 another class of activities. In other words, the sensation accompanying 

 a given color presentation is not due to the vibrations in the visual center 

 in the occipital lobe, but to the state of cortical equilibrium or the equation 

 of cortical excitement when that color stimulus predominates. Previous 

 vestigeal excitements and coordinations [associations, c. J. H., see p. 35] 

 with the data from other cortical centers all enter into the conscious pres- 

 entation. As the wave of excitation passes from the visual center to other 

 parts, the proportional participation of other centers increases, producing a 

 composite containing more distantly related elements." 



"Every specific sense-content with its escort of reflexly produced associ- 

 ated elements causes a more or less profound disturbance of the psychical 

 equilibrium, and the nature of this disturbance depends not only on the 

 intensity and state of concentration, but very largely on the kind of equi- 

 librium, already existing. . . . The character of the conscious act (and 

 the elements of consciousness are always acts) will, of course, depend upon 

 the extent to which the several factors in the associational system partici- 

 pate in the equilibrium. Each disturbance of the equilibrium spreads from 

 the point of impact in such a way that progressively more of the possible 

 reflex currents enter the complex, thus producing the extension from mere 

 sensation to the higher processes of apperceptive association. A conscious 

 act is always a fluctuation of equilibrium, so that all cognitive elements 

 are awakened in response to changes rather than invariable or monotonous 

 stimuli." 



The dynamic view of consciousness here adopted makes such 

 expressions as "the unconscious mind" impossible contradic- 

 tions. Either the mental functions are in process or they are 



