GENERAL DISCUSSION 663 



bv the central nervous system. Presumably such analysis has to be attributed to the 

 operation of spatio-temporal patterns of neuronal activit)-. 



I a^ree that the phenomena of attention and of the orienting reflex are of great 

 importance in a fullv developed theory of conditioning. I would suggest that 

 cortical inhibition is somehow involved in suppressing much of the developing 

 neural activitv that would otherwise arise from the sensory input and that is being 

 rejected. Already there are many instances of inhibition operating on the earliest 

 synaptic relays on sensory pathways. The orienting reflex can be regarded as 

 operating to increase the level of excitability in the convergence centre, which 

 consequently functions more effectively and nitensely. 



Related considerations help to answer Dr Doty's criticism. The temporal sequence 

 for effective conditioning can be accounted for by postulating that CS has to 

 develop its specific spatio-temporal pattern of activity in CC, possibly of rcverbera- 

 torv character, before the application of the dominant US. It is helped to do this 

 bv the background excitation added by the orienting reflex. But for this temporal 

 sequence, the US would dominate the neuronal activity of CC and NN to the 

 exclusion of CS, and as a consequence there would not be the development of the 

 specific patterns of mcreased synaptic efficacy that arise b\- the conjoint CS and US 

 input. I think Dr Lashlcv in the Hixon Svmposium greatl\- underestimated the 

 time that could be occupied in developing specific patterns of neuronal activit}- in 

 the unimaginably complicated networks of the cerebral cortex. The events in- 

 volved are of a different order of complexity compared to physiological reflex 

 phenomena. 



I haven't yet answered all of the specific criticisms, but perhaps I have indicated 

 the way in which necessary development of the hypothesis can occur. We would 

 all agree that conditioning must be explained in terms of neural changes and that 

 immensely complex neural pathways are concerned. The hypothesis that I have 

 proposed merely attempts to show how the physiological properties that have been 

 experimentally demonstrated for the synapse can account for conditioning, given 

 the complexity of pathways that forms the basis of all our thinking about higher 

 nervous activities. 



Anokhin. I should like to remark that there are two tundamentalK' distinct 

 phenomena, which are usually confused w'hen discussing the problem of the 

 formation of conditioned-reflex connections. 



The first phenomenon is the property of the nervous tissue to retain a succession 

 of any stimuli provided they be above threshold. This is a characteristic of the 

 nervous matter, it occurs irrespective of which stimulus follows which, whatever 

 their order and even irrespective of w^iether or not these stimuli contribute some- 

 thing significant to the life of the organism, in the wide biological sense. 



The second phenomenon is the genuine conditioned reflex, i.e. a constant 

 succession of stimuli ending b}' some purposeful adjusting effect for the organism, 

 i.e. a succession of stimuli consolidated by a final emotional effect, the uncondi- 

 tioned stimulus. 



