266 Information Storage and Neural Control 



using only the peripheral conditioned stimuli. Only central se- 

 quences bracketed by correct performance to the peripheral 

 stimulus alone were considered acceptable. 



Intensive studies of the effects of concurrent central and peri- 

 pheral stimulation have been carried out in two cats. One of these 

 animals (Cat 4) was conditioned to press a lever to avoid shock 

 within fifteen seconds after the onset of a four per second flicker, 

 but was punished if lever press was performed during" a ten per 

 second flicker. The other animal (Cat 10) was trained to the 

 opposite significance of flicker frequency, pressing" the lever to 

 ten per second flicker but not to four per second. Results of the 

 concurrent stimulation studies on these two animals are sum- 

 marized in Table I. 



Note that the data show, at a very high significance level, that a 

 four per second electrical stimulation of the visual cortex is much 

 more effective than a ten per second input in achieving inhibition of 

 conditioned avoidance response performance to a simultaneously 

 presented TCS in both Cat 4 and Cat 10, although the meaning 

 of a four per second flicker was opposite for these two animals. 

 Since this was true both for central stimuli of equal burst duration 

 and for those of equal energy, the severe disruption can be at- 

 tributed to the frequency of the simulated input. Four per second 

 central stimulation was much more inhibitory than ten per second. 

 This effect was not observed in auditory or medial suprasylvian 

 cortex, but appeared to be rather specific for the cortex of the 

 CS modality. This suggests that the input in some way interferes 

 with activity in the visual system and that the visual cortex or 

 regions to which it projects are involved in the mediation of the 

 conditioned response. Such conclusions would be consonant with 

 those of Zuckermann (27), who observed interference with per- 

 formance of conditioned responses to visual stimuli during after- 

 discharge following stimulation of visual cortex but not of motor 

 cortex or reticular formation. Such a conclusion is difficult to 

 reconcile with the remarkable ability of Cat 4 to sustain appropriate 

 behavioral response to a four per second flicker when 2.5 times 

 more electrical energy was applied to the same visual cortex at 

 ten per second. In contrast to the cortical current values for dis- 

 ruption, note the exceedingly low current required in subcortical 



