Information Storage in Nerve Cells 



191 



RC 

 LC 



Mm 



v/-^^^v^MVUWv^ 



Tone 



'^^^-h^^ 



t Stim. 



■U .J 





B 





I stim. off 



Fig. 1. Initial trial in which a low intensity 500 cycle per second tone lasting 

 ten seconds is paired with four per second shocks (6 volts, 1 millisecond duration) 

 delivered through bipolar stimulating electrodes in the left centre median. The 

 tracing is from an unesthetized rabbit. Electrodes derived from the somato- 

 sensory regions of both hemispheres and recorded monopolarly to a reference 

 on the pinna. A and B are a continuous sequence, (A) indicating the pronounced 

 negative shift witli slight after-positivity on the onset of thalamic stimulation 

 and (B) the reversal of steady potential shift at the cessation of thalamic stimu- 

 lation. Note that the steady potential change is limited to the ipsilateral hemi- 

 sphere. Calibration: 50 microvolts and one second (37). 



R C r 



L C 



•Jr, V^/.V 



^>^^^.-^/V■•f'^^^ '^V^ ^ . , 



^YKr}r^f'r,^\-J^r^\j'. --r ' 



Tone 



•/ V ../I 



Fig. 2. Same experiment as in Figure 1. After forty trials the tone alone elicited 

 the same ipsilateral negative-positive steady potential shift. This gradually dis- 

 appeared over a series of sLx unreinforced trials but was restored by a single 

 subsequent reinforcement witli thalamic stimulation. Calibration: 50 microvolts 



and one second (37). 



