8 PHYSIOLOGICAL TRIGGERS 



higher level events (metamorphosis, diapause, ovulation, instinctive behavior) 

 would turn out to be essentially triggered over-all phenomena but to consist 

 of a complex of substituent processes, some continuously graded, others triggers, 

 or even chains of triggers within triggers. We have the reciprocal case, too, 

 where a graded event (e.g. the synaptic potential) is believed to consist of a 

 large population of triggered molecular events in the membrane. 



The distinction here emphasized is the same as that between digital (trig- 

 gered) and analog (graded) signals. We shall see in the several papers how com- 

 plex is the interrelationship between these, each one entering into the makeup 

 of the other and each succeeding the other temporally in different cases. We see 

 this especially clearly in the nervous system and sense organs where, as our 

 authors point out, graded transducers convert stimuli of external origin into 

 triggered impulses, which in turn may contribute at some more central junction 

 to a presynaptic barrage which is again transduced, first to analog and again 

 to digital events. 



But for all the wealth of information, it may be well to end by pointing out, 

 as an example of our ignorance of physiological events, the gap between this 

 relative wealth at the neuronal level and the relative wealth at the levels of 

 brain stimulation and recording and of intact animal behavior. The first level 

 is far removed from the second and third. In between we have still to identify, 

 in structural substrata and functional relation, even in formal black boxes 

 and labeled arrows, the parameters of the triggers and levers that integrate, 

 initiate, pattern, associate, memorize and feel. 



