THE FUNCTIONS OF THE CEREBRAL CORTEX 295 



parison of the brains of the higher apes with that of man (Figs. 

 132, 133), and of the lower races of men as contrasted with the 

 higher. In our own mental life we recognize the persistence of 

 traces of previous experience subjectively as memory, and mem- 

 ory lies at the basis of all human culture. From this it follows 

 that psychological memory is probably a function of the associa- 

 tion centers; but it must not be assumed that specific memories 

 reside in particular cortical areas, much less that they are pre- 

 served as structural traces left in individual cortical cells, as has 

 sometimes been done. 1 



The simplest concrete memory that can appear in conscious- 

 ness is a very complex process, and probably involves the activity 

 of an extensive system of association centers and tracts. That 

 which persists in the cerebral cortex between the initial experi- 

 ence and the recollection of it is, therefore, in all probability a 

 change in the interneuronic resistance such as to alter the 

 physiological equilibrium of the component neurons of some 

 particular associational system. What the nature of this change 

 may be is unknown, but it is conceivable that it might take the 

 form of a permanent modification of the synapses between the 

 neurons which were functionally active during the initial experi- 

 ence such as to facilitate the active participation of the same 

 neurons in the same physiological pattern during the reproduc- 

 tion. 



That which we know subjectively as the association of ideas 

 may, in a somewhat similar way, be pictured as involving neuro- 

 logically the discharge of nervous energy in the cortex between 

 two systems of neurons which have in some previous experience 

 been physiologically united in some cortical reaction. If, for 

 instance, I heard a song of a mocking bird for the first time last 

 year while walking in a rose garden, upon revisiting the gar- 

 den I may recall the song of the bird. Here the sight of the 

 garden (a highly complex apperceptive process involving many 

 association tracts) actuates neuron system number one domi- 

 nated by present visual afferent impulses, and the association 



1 These residua of past cerebral activities form the basis of those char- 

 acteristic "brain dispositions" which are important factors in each person- 

 ality. They have been termed "engrams" by Semonand "neurograms" by 

 Morton Prince (see Prince, The Unconscious, Chapter V, New York, 1914). 



