ANALYSIS OF SOME EVOKED SYNAPTIC ACTIVITIES 



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Fig. 5. Changing characteristics of distant s.c.r.'s during second postnatal week. 

 A-D. Relationship between near (upper channel) and distant (lower channel) 

 responses recorded at distances from stimulating electrodes indicated at left in 

 each series; ages shown above. A. S.c.r.'s at 5 and 3 mm larger than at 2-5 and 

 4 mm. B. Reinforced responses at 4 and 6 mm. c. Note extraordinary magnitude 

 of response at 4 and 6 mm. d. Reinforced s.c.r. at 8 mm; latency about 25 msec. 

 In c records at bottom of column taken before and after topical application 

 of 1 % GABA to near electrode site. In this record, upper channel shows abolition 

 of surface-negativity and unmasking of surface-positivity after GABA; lower 

 channel shows two perfectly superposable distant responses, e. Comparison of 

 responses at indicated distances in a 14 day-old-kitten and adult cat studied 

 under identical conditions. Wire electrode (0- 1 mm) employed to record response 

 at 0-3 mm in kitten. Compare characteristics of responses at 1 mm. Duration 

 of the distant response in adult preparation is similar to that of near response. 

 Cals. 100 c/s; 0-1 mV in a; 0-3 mV in b-e; that for d shown in e. 



responses of extraordinary magnitude relative to near s.c.r.'s are detectable 

 in favorable preparations (Fig. 5). Brooks and Enger (1959) analyzed this 

 phenomenon in adult cats and concluded on the basis of peak-latency 

 measurements that distant "reinforced" responses were propagated outward 

 from the site of stimulation more rapidly than near s.c.r.'s. In the immature 

 cortex, the latency of s.c.r.'s, as measured to onset of response, increases 

 linearly with distance (Fig. 5). 



In addition to changes in overall duration, propagation velocity, and 

 spread, s.c.r.'s also exhibit a change in the early phase of their activity cycles 

 during postnatal ontogenesis (Purpura et al, 1960a). This alteration occurs in 

 the first week and consists in a decrease in the absolute unresponsive period 

 (a.u.p.), as determined by short-interval paired conditioning-testing stimuH. 

 The a.u.p. in neonatal animals (<3 days old) is 4-8 msec, and 1-2 msec by 

 the end of the first postnatal week. Activity cycles are identical for near and 

 distant responses. It is of interest that the time of appearance of distant 



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