134 BRAIN MECHANISMS AND LEARNING 



In 195 r, while working in the laboratories of P. S. Kupalov seeking further 

 confirmation of the hypothesis of 'shortened conditioned reflexes', it was 

 discovered that conditioned reflexes could readily be formed by pairing 

 stimuli at two cortical points (Giurgea, 1953 a, b). Stimulation of occipital 

 cortex w^hich is initially without apparent effect ultimately produces 

 movement highly similar to that elicited by the stimulation of the sigmoid 

 gyrus with which it is paired. This direct contradiction of the results of 

 Loucks seems best explained by differences in the timing of presentation 

 of stimuli. In all his experiments Loucks (1935) used intertrial intervals of 

 2 minutes or less, usually 30-60 seconds, whereas an intertrial interval 

 of 3-5 minutes was used in our experiments. If the intertrial interval is 

 reduced to 2 minutes even after such CRs have been established, the CRs 

 disappear in the majority of dogs tested so far (Giurgea, 1953 a, b), 

 although the unconditioned response (UR) is unaffected. 



Continuing these studies, it has been shown that formation of CRs by 

 cortical stimulation is not dependent upon sensory endings in the meninges 

 since the CR may be readily established after destruction of the Gasserian 

 ganglion (Raiciulescu, Giurgea and Savescu, 1956). A CR established to 

 stimulation of parietal-occipital cortex as CS was also elicited by a tonal or 

 photic CS (Giurgea and Raiciulescu, 1957). In two animals with total, 

 histologically confirmed section of the corpus callosum CRs were 

 established even though CS and US were applied to different hemispheres 

 (Raiciulescu and Giurgea, 1957; Giurgea, Raiciulescu and Marco vici, 

 1957). The electrical activity recorded from the US area does not appear 

 to be changed by this conditioning procedure and is within normal limits 

 of low voltage, fast activity very shortly after the US is applied (Giurgea 

 and Raiciulescu, 1959). In none of these experiments does the behaviour of 

 the dogs indicate even the slightest element of motivation. This impres- 

 sion has now been conhrmed objectively in the experiments reported 

 below. 



TECHNIQUE 



The experiments at Michigan have so fir been performed on four dogs, 

 two cats and two cynomolgous monkeys. The dogs are restrained easily 

 by placing their legs through plastic loops (e.g. Fig. i). Cats are held by 

 placing their heads through a heavy plastic stock leaving their limbs free. 

 Monkeys are kept permanently seated in a Lilly-type chair (Mason, 1958). 

 All animals are adapted to restraint prior to electrode implantation. 

 During the experiment the animals are isolated and observed through a 

 'one-way' glass. 



