CONTACT RECEPTORS IN MEMORY 159 



is started at one time may be completed later. This 

 ability of brain cells to store nerve impulses is called 

 memory, and is the basis for the use of past experience. 



It should be remembered that all experience is based 

 upon the stimulation of receptors, and the machinery of 

 memory is a machinery for storing the impressions which 

 these stimuli impart, for use at some future time. An 

 impression once stored in the form of memory may serve 

 as the starting point for activity not once but repeatedly, 

 thus making a single memory able to bring about many 

 actions and so contributing greatly to the utility of 

 memory. 



Contact Receptors Participate in Memory. — In 

 practically all animals which have a brain the contact 

 receptors and probably the internal receptors as well have 

 indirect communication by means of connecting nerve- 

 cells with the brain (Fig. 44), so that when any of the 

 sense organs are stimulated it is probable that nervous 

 impulses will pass into the brain. In the case of most 

 contact receptors this connection with the brain would be 

 called a secondary connection, the primary connection 

 being with the motor nerve-cells. When receptors having 

 this kind of connection are stimulated the ordinary reflex 

 response follows at once, automatically, and at the same 

 time there is a flow of nervous impulses into the brain. 

 Those which pass to the brain register there as memories, 

 just as do the impulses coming more directly from the 

 distance receptors. Thus all the channels of experience 

 become available for the future guidance of the animal. 



Association. — Memories are made serviceable by a 

 further property of the brain-cells to which we give the 

 name of association. This is the grouping together of 

 memories that are related so as to form other and more 

 complex memories. The best way to show the signifi- 

 cance of association is by illustration. It is customary 

 to use for the purpose of illustration the case of a baby 

 that starts life without any background of experience 



