146 BRAIN MECHANISMS AND LEARNING 



US with lever-prcssiug there is equally convincing circumstantial evidence 

 for the absence of motivation in these conditioning procedures. The 

 extreme brevity of electrocortical arousal follow^ing the CS-US com- 

 bination in Cat 48g, or Monkey 1 closing its eyes to doze with onset of the 

 CS, is scarcely expected from motivational stimuli. Nor are these CR 

 movements purposeful; rather they are physiological absurdities. They 

 seldom prepare the animal posturally for the ensuing UR and more often 

 than not the CR is terminated before the UR begins. Watching Monkey 1 

 day after day raise its arm to stimulation of its 'visual' cortex one could not 

 escape the feeling that this nonsensical yet persistent movement was some- 

 how analogous to the compulsive movements of neurotic humans. 



The work of Segundo and his colleagues, reported at this meeting and 

 elsewhere (Segundo, Roig and Sommer-Smith, 1959), in which a tonal 

 CS evokes movements similar to those elicited by electrical stimulation of 

 centre median or the mesencephalic reticular formation as US, provide 

 excellent confirmation of our observations — movements produced by 

 central stimulation can be conditioned. Masserman's failure to obtain such 

 results from hypothalamic stimulation (Masserman, 1943) stands in sharp 

 contrast to the results with Doi^ Gaiiiiiia and the work of Segundo et al. 

 Obviously the hypothalamus must be carefully re-examined in this 

 regard. The US in the experiments 9f Segundo et al. probably produced 

 motivational effects in some of their animals, but in others it appears less 

 clear. In any event it would be difficult to ascribe some 'biological 

 significance' or appropriateness to the movements induced by the CS. It 

 is equally difficult to find a motivational basis for the 'backwards' type of 

 conditioning linking the US with the CS as analysed by Asratyan in this 

 volume. 



Since CRs can be established without a motivational factor, there is 

 more hope that the basic phenomena of learning can be sought in neural 

 systems sufficiently simple for meaningful analysis, perhaps with purely 

 electrophysiological techniques. The temporal factor appears to be critical 

 and the experiments with Doi^ Gaiiiiiia and especially Doo Epsilon show 

 the conditioned state is not established by the repeated, randomized 

 excitation of US and CS systems. 



Several observations support Sperry's hypothesis (1955) that the signi- 

 ficant alteration is to be sought in the effector system. In motivated condi- 

 tioning an alteration in excitability specific to the limb being conditioned 

 can be observed some time before any CRs appear (Doty and Rutledge, 

 1959)- In the present and earlier experiments (Giurgca, 1953 a, b) move- 

 ments similar to the CR, never seen previously in the animal's behaviour, 



