54 hiformation Storage and Neural Control 



more quickly, or to overlook completely otherwise obvious solution 

 paths in a problem situation. If one were to instruct a computer 

 so that it had this capability, it would be required that the set 

 information, given before the critical task, provide information 

 (or set switches) at a number of different places in the piogram. 

 This is generally accomplished by setting a "flag," which is tested 

 by various subroutines, or by setting several flags, one in each 

 subroutine. The result is a memory structure which might be 

 called diffusely localized. This type of signal must be extremely 

 flexible, and must be controlled by the executive program; i.e., 

 it must be at a higher level in the process structure. To my knowl- 

 edge, no information exists concerning the cerebral mechanism 

 which could explain such a phenomenon, nor has anyone worried 

 much about it. Although perhaps other mechanisms are con- 

 ceivable, it seems necessary that communication channels of some 

 sort must exist between the higher control centers and several 

 lower centers, or that the nerve nets which define processes must 

 be constructed so that they can be rapidly, but temporarily altered 

 by some signal in a higher control center. 



Finally, I wish to point out a feature underlying all of the 

 computerized brain models which deal with the learning or growth 

 of connections between neurons. Such models have been proposed 

 as the basis for such complex functions as pattern recognition 

 (Rosenblatt, 22); yet each rests on fairly simple and standard 

 assumptions of the sort discussed above in connection with Hebb's 

 growth hypothesis: "If neuron B fires immediately after neuron A, 

 the probability increases that A will fire B." Although such a 

 process is quite feasible, no direct physiological evidence defines 

 its mechanism, so the assumption remains a psychological one. 

 It is almost certain to be correct, and yet perhaps we should not 

 give up the search for alternate mechanisms — if not to replace 

 this notion, then to complement it. For example, the firing of 

 neuron A followed by the firing of neuron B might increase the 

 efficiency of all other connections at the A-B synapse as well. Or 

 perhaps the A-B "growth" takes place only if B subsequently fires 

 C, which bears some relation to A. The neurological mechanisms 

 underlying these suggestions are not so plausible as those of the 

 Hebb hypothesis, but if they are true they might have a profound 



