270 BRAIN MECHANISMS AND LEARNING 



sensory cortex. A detailed report covering cortical evoked potentials in 

 free, inianaesthetized cats is ni preparation (Roig, Segundo, Soninier- 

 Smith and Galeano, to be published): it will indicate that, in 'chronic' 

 cats cortical responses to single subcutaneous shocks consisted (when 

 recorded as described above) in a succession of positive (P) and negative 



POTENTIAL EVOKED BY SUBCUTANEOUS SHOCK 

 ON CSC 



Fig. 3 

 potential evoked by single subcutaneous 

 shock on contralateral sensory cortex: 

 (unless specified otherwise, records from all figures 

 arc from sensory corte.x contralateral to peripheral 

 shocks). As recorded with equipment described 

 in text, potentials consisted in a succession of 

 positive (downward deflections P) and negative 

 (upward deflections N) peaks named, according 

 to polarity and chronological order of pre- 

 sentation. Pi, Ni, P2, N2, P3 and N3. Arrow 

 indicates application of subcutaneous shock. Cali- 

 brations: 20 uv., 50 c.p.s. (as in all figures using 

 cathode ray oscilloscope), CSC, contralateral 

 sensory corte.x; SUBCUT., subcutaneous. 



(N) peaks, tentatively named as follows (Fig. 3): Pi (initial positive spike) 

 was comparable to that encountered regularly but designated variously 

 and ascribed to presynaptic activation in specific terminals (Figs. 3, 6, 8, 

 9, II, 12). Ni was similar to first part of subsequent negative wave 

 (Figs. 3, 6, 8, 9, 10, II, 12). P2, N2 and P3 constituted a variable sequence 

 exhibiting similarity with 'augmenting' complexes; when N2 was absent. 



