416 



L. TOWE 



cuneate nucleus. The conditioning input had a weak excitatory effect, produc- 

 ing one spike in twelve of a hundred trials. The testing input produced three 

 spikes in sixty-eight of a hundred trials and two spikes in the remaining 

 thirty-two trials. When the conditioning digit was stimulated 12 msec prior to 

 the testing digit, the test response latency increased significantly, the number 

 of spikes in each discharge decreased, and the interspike interval increased 

 by a small, but statistically significant amount. The same sort of interaction 

 in the cortex shows considerably greater variability, but also a larger change 

 in latency. 



Thus, with any particular unit, both the "increasing latency" and the 

 "decreasing latency" types of interaction should be demonstrable. Figure 5 

 shows that this is indeed the case, and summarizes both effects. Both digits II 

 and III were near the center of the unit excitatory receptive field ; digit Y was 

 on the border of the field. Interacting stimulation of digits II (testing) and III 



m+i 



Bz+n 



S+E 



2. 



S/d 



\rL 



U- 



Fig. 5. Unit isolated 832 /t below pial surface in p.c.g. Digit II was center of unit 

 excitatory receptive field;/? = 0-95,L = 13-76 msec, s = 0-51 msec, J/'/ = I'll. 

 Unconditioned testing L (digit II) shown as line through each L graph ; shaded area 

 shows one standard deviation in each direction from L. Height of line at 

 C — T = msec, topped by bar, shows conditioning digit response probability. 

 Conditioning digit II by digit III yielded "occlusive"" interaction, Z shortened 

 and 5/7/ increased, until p = and during recovery. Conditioning II by V yielded 

 "inhibitory"' interaction: L increased and sjci dropped to TOO. Conditioning II 

 by IV yielded an intermediate or mixed interaction, i.e. it began like a weak 

 "occlusive"' interaction, but other properties suggest the presence of a strong 



inhibitory effect. 



