632 PHYSIOLOGY CHAP. 



alternative, we must assume that " the sensory and motor centres 

 serve only for immediate and ever new reactions, of which they 

 preserve no impressions that the enduring or incomplete memory 

 of events which affect the projection centres are stored up in 

 other centres that the images of things are perceived at, one point 

 and retained at another . . ." (Tanzi). 



This hypothesis seems to us to be an arbitrary interpretation 

 of Flechsig's theory. Prior to the distinction of the cerebral 

 cortex into projection fields and association fields, when the brain 

 was simply held divisible into sensory and motor spheres, it was 

 natural to assume that the memory of sense impressions was 

 distributed all over the cerebral cortex. That the association 

 fields are the exclusive seat of memory, and that the projection 

 fields which are in the most immediate connection with the 

 peripheral sense organs are incapable of preserving the impressions 

 and percepts, is a necessary consequence of Flechsig's theory. 



The occurrence of blindness of cortical origin without loss of 

 the power of evoking visual images, does not prove (as stated by 

 Tanzi) that the centre of visual memory is distinct and separate 

 from the area of visual sensibility. When we consider that visual 

 memory may theoretically be divided into functionally distinct 

 components, as the special memories of luminosity, colour, form, 

 dimensions, etc., it seems legitimate to assume that the lesions 

 which produce cortical blindness do not destroy the whole visual 

 fields, and do not therefore blot out the whole of the visual 

 memory stored in the cortex. 



No argument in fact prevents us from assuming that all 

 cortical areas, not excluding those in most intimate relation with 

 the peripheral sense organs, are the seat of special memories and 

 contain the traces of previous percepts and representations ; that 

 these impressions, organically distributed over countless elements, 

 are in more or less close inter-relationship, and are capable of 

 associating or combining in a thousand different ways. 



This theory of memory agrees perfectly with the results of 

 psychological analysis of perceptions in contrast to simple 

 sensations ; a perception results from the synthesis of a sensory 

 image with the mnemonic traces left by preceding sensations. The 

 sensory centres of the cortex which are the seat of perception are 

 accordingly capable of retaining memory impressions. 



On the other hand there can be no doubt that the greater 

 number of the nerve elements concerned with memory must be 

 sought in the association areas of the cortex. The physiological 

 proof of this is the amnesia of varying kind and degree produced 

 by alterations of these areas. The psychological proof lies in 

 the analysis of representations, in so far as these result from 

 association of the multiple and varied memory images which arise 

 in distant and distinct areas of the cortex. 



