282 BRAIN MECHANISMS AND LEARNING 



2. LoaiJi^iitioii specif city. After establishment of learned responses to T 

 by the usual practice of associating T with cessation of SS (to left foreleg), 

 routine was changed in three cats. Thereafter, SS were applied separately 

 to right and left forelegs: presentation of T during SS to left foreleg was 

 followed (as before) by substraction of shocks; presentation of T during 

 SS to right foreleg was not followed by change in shocks. Cats reacted to 

 this procedure as follows: (i) in two preparations, efficacy of T during left 

 SS was not modified and, m addition, application of T during SS to right 

 foreleg led, from the beginning, to identical behavioural and EEG effects 

 (that, since SS continued, were transitory) (generalization) (Fig. ii —II); 

 (ii) in the remaining animal and after a brief initial phase of generalization, 

 responses to T (during excitation of either leg) became unpredictable. 

 Therefore, 'differcntation' could not be established in the sense of restrict- 

 ing T influence to effects of SS applied to one single foreleg. 



(3) Modality specificity. A repetitive flash (Fl.) was used as non-somatic 

 excitation. Flicker did not cause behavioural responses (except for initial 

 orienting reflexes) : hence, considerations refer exclusively to the electro- 

 graphic sphere. In a first effort {a) SS and Fl. were applied separately, T 

 being followed by cessation of SS but not of Fl.: no differentiation 

 occurred (T continued to mask somatic and visual potentials). In a second 

 effort [b] Fl. was presented continuously during the entire session; SS was 

 applied intermittently and interrupted following T in the usual way. 

 With this technic]ue successful 'differentiation' took place: T application 

 modified potentials evoked in somatic sensory cortex by SS but did not 

 usually alter responses elicited at the same time in visual area by flashes 

 (Fig. II- III). 1 



Concomitantly with observation of behaviour and with sampling of 

 activity from sensory cortex (contralateral to SS), EEG records were taken 

 from different regions of the central nervous system comprising (in the 

 entire series) sensory cortex (homo-lateral to SS) HSC, acoustic cortex, 

 visual cortex, NMDT, MRF and MCG. If activity in these areas exhibited 

 relatively large voltage, slow waves and/or spindles during silence, 

 application of T (producing typical effects in contralateral sensory cortex 

 (CSC) could be followed by shift to low voltage, fast patterns (EEG 

 'arousal'). This was particularly consistent in HSC (three cats) and NMDT 

 (one cat): EP masking was never encountered without 'desynchroniza- 

 tion' appearing in HSC or NMDT. This was not always the case with 



1 Effort (/)) succeeded in producing 'modality' specificity whereas effort (a) did not. Failure 

 to establish localization specificity (see above) may have been due to application of a routine 

 similar to that of (i?) to a problem that might have been solved by a routine similar to that 

 of(b). 



