GENERAL DISCUSSION 65 I 



THIRD topic: location of plastic change 



KoNORSKi. To open the discussion on this topic I would hkc to emphasize the 

 radical change in our views, concerning the location ot plastic changes, which 

 took place in the last decade or two. At the end of the nineteenth and in the first 

 half of the present centurv the view was held that the abilit\' to form new inter- 

 neural connections is a characteristic of only higher parts of the nervous system, 

 and in higher animals chieHy, or even exclusively, of the cerebral cortex. The 

 lower parts ot the nervous system were supposed to be endowed with inborn 

 connections only, i.e. connections developed durmg ontogeny independently of 

 the animal's experience. The chief protagonist of this view was Pavlov, who main- 

 tained that the functional specificity of the cerebral cortex lies in the formation of 

 acquired connections; i.e. that the cerebral cortex may be considered as an organ of 

 conditioning. According to Pavlov, the decorticate animal retains the whole 

 repertory of inborn, or unconditioned reHexes (including instincts) but is not able 

 to form conditioned connections on their basis. 



However attractive this view, it proved with the lapse of time more and more 

 inadequate. On one hand it was shown that manv innate activities (unconditioned 

 rertexes) depend on the cerebral cortex. To give some examples: according to the 

 well-known studies ot Bard and Brooks placing and hoppmg reflexes depend on 

 the sensory-motor cortex, maternal behaviour, as shown by Beach, depends on the 

 medial parts of the cerebral cortex, and so on. A great body ot evidence showing 

 the role of the cerebral cortex in the course ot unconditioned reflexes was recently 

 given by Dr Asratyan. 



On the other hand we have now a rapidly increasing amount of evidence to 

 show that lower parts of the nervous axis are also apt either to form new inter- 

 neural connections, or to ameliorate the existing ones, according to new 'experi- 

 ences' (i.e. combinations ot stimuli). Much evidence of that kind was presented at 

 the present symposium b\- Or Eccles and Dr Hernandez-Peon. 



Therefore, it seems that the time is ripe to abandon the old view and to accept a 

 new one, according to which the ditFerence between the lower and the higher 

 parts ot the nervous s)stem is not that the first of them control inborn activities and 

 the second acquired activities, but that the higher the centres, the greater is the 

 complexity of activities controlled by them. And so those forms of plastic changes 

 which correspond to the level of functional complexity proper to the sp)inal cord 

 can occur at the spinal level, as shown in l^r Hernandez-Peon's experiments on 

 habituation to somatic stimulations or in l^r Eccles's experiments on the increase of 

 spinal reflexes by use. Some simple tonus ot conditioning and even diftcrentiations 

 can be established 111 decorticate animals according to the structural complexity of 

 the centres involved. But those learning processes, as well as unconditioned 

 reflexes, which require for their occurrence a complex analysis of external stimuli, 

 such as patterned vision or sound patterns, are mediated by particular areas of the 

 cerebral cortex. The examples ot such learning processes were given at this 

 symposium in the papers of Dr Myers, Dr Chow and my own. 



