26o 



BRAIN MECHANISMS AND LEARNING 



visual cortex derivations. Unit discharge in the visual cortex was observed to 

 increase upon the presentation of both conditioned and unconditioned stimuli and 

 the same augmented response to both signals was noted in a spontaneously firing 

 unit of nucleus ventralis anterior. Units in both the mesencephalic reticular 

 formation and the hippocampus no longer responded to cither stimulation nor did 

 any further responses develop even when trials were continued to as many as one 

 hundred. 



Table I 



PATTERN OF UNIT DISCHARGE DURING DEVELOPMENT 

 OF CONDITIONED ELECTRICAL RESPONSE 



* Relay nuclei in Auditory System not monitored. 

 I > 50 per cent increased firing, 

 i > 50 per cent decreased firing. 

 o No change. 



Table I presents a summary of these data. The findings suggest that some sequen- 

 tial pattern of involvement does indeed exist. However, the interplay of these gang- 

 lionic systems, if changes in one can be assumed to be related to changes in any 

 other, does not provide evidence of any one-to-one relationship such that excita- 

 tion of one area can be assumed always to inhibit or activate another area. For 

 example, the proposal of Lissak and Grastyan (1957) that the hippocampus exerts 

 an inhibitory influence on the ascending reticular activatiiiir svstem is borne out 



