144 BRAIN MECHANISMS AND LEARNING 



threc-niiiiute intervals nincty-onc couplings were administered in twelve 

 sessions. Then after a hiatus of 25 weeks another 116 combinations were 

 given with two-minute intervals in three sessions and eighty-five com- 

 binations at four-minute intervals in four sessions. Finally, 265 couplings 

 were given automatically at four-minute intervals in two overnight 

 sessions, but still without indication of conditioning. 



The animal was then conciitioned to avoid a shock to the tail by pressing 

 a lever. The first CR to a tonal CS required 105 trials and 238 trials to 

 attain twelve avoidances in twenty CS presentations. Generalization to 

 other auditory conditional stimuli was immediate and complete. The 

 cortical CS was then employed. For 300 conabinations of this CS with the 

 tail-shock US there was, judging by the animal's general behaviour and 

 visually obscrveci respiration, no anticipation whatever of the impending 

 shock during a four-second CS. Yet on every presentation the CS was 

 patently effective since the eyes moved persistently down and to the right 

 during each stimulation. The first CRs occurred after the CS was in- 

 creased to 1.2 niA. The threshold was ultimately determined to be 0.6 

 mA. for the elicitation of this CR. 



Cat ^2^. Conditioning with cortical stimulation was likewise a failure 

 in this animal; but so too was conditioning using an auditory CS and 

 foot-shock as US. The animal was also seizure-prone. A total of 345 

 pairings of a right middle ectosylvian gyrus CS with right ansate gyrus 

 US produced no CRs, and 420 pairings of a tonal CS with foot-shock US 

 was almost equally ineffective although a few CRs were seen. 



Cat 48g. This animal has been thoroughly studied by Allan Minster. 

 The CS applied to right middle ectosylvian gyrus usually elicited no overt 

 response initially at the currents used. At higher currents the animal 

 looked up and to the left. The US in the right ansate area produced an 

 abrupt turn of the head to the left and flexion of the left foreleg. The first 

 CR occurred on tlie thirty-ninth pairing, fifth session. These CRs, how- 

 ever, never became consistent from one session to the next. In 100 trials 

 after the first CR there were a total of only thirty-two and fifteen of these 

 were made in three of the fifteen sessions. At first, the CR was a vigorous 

 lifting and extension of the left foreleg, but after the seventy-second pair- 

 ing the right foreleg executed this same movement to the CS more often 

 than did the left. The threshold for CR elicitation by stimulation of middle 

 ectosylvian gyrus was probably about 0.8 mA. Stimulation of the right 

 posterior ectosylvian gyrus at 0.35 mA. yielded seven right and one left 

 foreleg CRs in eleven presentations. To date, ninety-seven pairings of the 

 right ansate US with a CS applied to left middle suprasylvian gyrus 



