GENERAL DISCUSSION 643 



bricriv passing the resting threshold. Atter this phase ot higher irritabiht\- it tails 

 back to the normal resting threshold, hi the unstable neurones the excitability, and 

 with it the readiness to response, builds up until the thresholci of release is reached 

 bv itseh and a spontaneous discharge can take place. Between these two extremes 

 all gradients can be found. If for example the resting and the response thresholds 

 become approximated one stimulus can lead to a self-perpetuating sequence of 

 discharges, as the curve ot excitability will repeatedly reach the releasing threshold. 

 Reflex behaviour alwa)s needs an input tor discharge and is therefore more strictly 

 under atf'erent control than the more spontaneous instinctive acts, which can go oft 

 in a vacuum. But normally thev, too, are released by certain key stimuli. 



Anokhin. When we speak ot inborn behaviour, we should bear m mind that all 

 our considerations can apply only to the very tirst acts ot the newborn, since the 

 first behavioural acts enrich the inborn tunctional s}stems by new afferent stimuli 

 trom the environment, hi practice we never get 'inborn behaviour' in its pure torm 

 after 2 or 3 days following the birth of an animal, although the end nucleus of the 

 reaction was included in the embr)-ogenesis on the basis ot the heterochronic 

 growth ot the nervous structures. 



This rule applies to such specific human behaviour as for instance the human 

 mimic reactions. As our research has shown, as early as on the 5th or 6th month oi 

 its prenatal lite, the human toetus is able to react to external stimuli by quite 

 diverse mimetic reactions. 



The emotional quality ot these reactions is so well determined that there can be 

 no doubt in the observer's mind: 'this is unpleasant!', 'it hurts!' 



Fessard. I think the use, or for some the abuse, of this expression 'inborn 

 behaviour' is also a question of doctrinal position. Our colleagues from Eastern 

 countries have the view some of us find too extreme that animal behaviour is 

 entirely determined bv the stimuli — either external or internal — present at every 

 moment. Most of us prefer making a sharp distinction between what comes trom 

 the outside world and what depends upon a set oi internal incitations organized 

 according to an inborn, and, so to speak, ever present pattern ot dynamic possibili- 

 ties, to which correspond certain structures within the central nervous s}-stem. 



Anokhin. In connection with the remarks made by Dr Eibl and with the 

 morphological assumptions on inborn behaviour, I should like to stress one physio- 

 logical teature in the heterochrony and s-\-stematic maturation of the nervous 

 structures in embryogenesis. We have been able to note the tollowing rules: the 

 tunctional system, which trom the morphological point of view has been formed 

 earlier than the other system, has a rather low threshold of excitability and there- 

 fore acts as the dominant function at that given stage of development. This means 

 that any internal or external stimulus, however small, will indeed first ot all 

 stimulate into action the dominant tunctional system. 



In this way the physiological predominance ot the functional systems which has 

 matured earlier than others is one of the decisive factors brniging about a high 

 adjustment and adequate timing ot inborn behaviour. 



TT 



