Summary and General Discussion 365 



a change in the sex cells; this change specifically favors the develop- 

 ment of a longer neck in the offspring giraffe — a truly formidable re- 

 quirement, which alone made Lamarckian inheritance improbable. 



Our demands are no less. We require, also, transduction from 

 a process to a structure and back to a process, from information 

 fiow to information storage to information retrieval. Nerve messages 

 and events must be fixed in some kind of stable architectural 

 alteration which favors regeneration of comparable events from 

 the system. The flow of information is a matter, essentially, of 

 action at synapses where nerve cells junction. Synapses can vary 

 only in number, or intensity, which is really equivalent; position; 

 kind, to some extent, as excitatory or inhibitory; and, of course 

 the temporal phase of their activity. There are no other parameters, 

 for these synaptic attributes also express the patterns of neuron 

 connectivities. 



The storage occurs during a period of fixation, as I have called 

 it, or consolidation, as Dr. Morrell called it, during which a 

 reversible change becomes irreversible and an enduring memory 

 is established. This engram probably includes a molecular change 

 and, as just discussed, may involve production of an altered mole- 

 cule or selection of a particular molecule from a pre-existent array. 

 Selection might be in position or in number as well as in archi- 

 tecture of molecules. Given the molecular change, still further 

 consolidation processes over time might well involve more gross 

 morphological changes, such as enlargement of end-feet or actual 

 sprouting of axon branches (there are many more in old neurons 

 than in young ones); but this is all guess work. Perhaps there are 

 only a given number of slots, so to speak, in which memories can 

 last, although any notion of one memory in one slot is untenable. 

 There is conclusive physiological and psychological evidence that, 

 at most, there are different arrays or patterns of neuron groups 

 which subserve different memories, with some spatial separation 

 as well as overlap. 



Then, finally, we must account for the ability of the particular 

 morphological residue left by a given pattern of impinging im- 

 pulses in turn to make the neuron sensitive to just that pattern of 

 impulses, so that in the future this input can fire the cell more 

 easily than other inputs. 



