174 BRAIN MECHANISMS AND LEARNING 



applied after one appearance or after several appearances of the unit 

 response. It was usually applied after each appearance of the response with 

 a delay of about i second (this was the experimenter's response tinae). 



The design of the experiment, when the stimulus was presented auto- 

 matically, is shown in Fig. 16. The output from the oscilloscope amplifiers 

 was led into an amplitude discriminator circuit, and the output from the 

 circuit activated an electronic counter which could be preset to deliver 

 stmiulation after a preset number of responses from i to 9. In this case, the 

 delay of reinforcement was about 3 msec. Each activation of the stimulator 

 was recorded on a cumulative response recorder, so that the response rate 

 was retained on a permanent record. 



In the case of a positive experiment, the single-unit response rate was 

 greatly augmented by either the hand or the mechanical reinforcement 

 procedure. The increased rate outlasted the procedure by a variable period 

 of time. Immediately after this procedure, a third record of the unit's 

 activity was made on film. It is the comparison of the three tilms that 

 comprises our data. 



In the event of failure to reinforce, by manual techniques, the unit was 

 often put on the automatic reinforcement procedure, and sometimes 

 positive reinforcement bypassed by the former procedure was discovered 

 after long runs with the latter method. Because of the close temporal 

 relationship between the control picture and the augmented picture, when 

 the manual technique was successful, it was always the more convincing. 



RESULTS 



The first point to emphasize is the difference between the neocortex and 

 the palaeocortical structures studied. Palaeocortical units often appeared to 

 'learn with ease'. Neocortical units never yielded any similar rapid modi- 

 fication when subjected to reinforcement techniques. The details of this 

 difference will be clarified below. Most often, stimulation caused neo- 

 cortical unit respc^nses to disappear, never to return; but sometimes, rein- 

 forcement caused slow augmentation of response. 



Where stimulation had any effect other than inhibition, it produced one 

 of four kinds of changes in the pattern of single-unit response: (i) conver- 

 sion of a sporadic grouped response to a continuous response by the 

 reinforcement procedure; (2) augmentation of the response rate of a 

 sporadic response by reinforcement; (3) ehcitation of activity imme- 

 diately after the stimulus, but only when it was given as a reinforcement; 

 and (4) ehcitation of activity by the stimulus irrespective of its use as a 

 reinforcement. 



