268 BRAIN MECHANISMS AND LEARNING 



(iii) same T when novel (on first presentation) (four cats) ; (iv) intense 

 crashing soiuid (three cats) ; (v) different frequency tone (CT) that signalled 

 SS initiation (tone conditioned in the usual sense) (Fig. iD) (two cats). 



Specificity of learned effects was tested by comparing them with con- 

 sequences encountered in slightly dissimilar circumstances as: (i) effect 

 of different frequency tone upon response to same SS (four cats); (ii) 

 effect of same T upon response to SS applied to different limb (three cats) ; 

 (iii) effect of same T upon response to different modality stimulus (repeti- 

 tive flash) (two cats). 



In three preparations, T and SS were alternated so that T initiation 

 preceded SS cessation by 5 seconds and T cessation was followed, 5 

 seconds later, by SS initiation (Fig. i E) : behavioural and EEG effects of T 

 initiation were identical to those encountered in remaining animals of this 

 group (in which tone cessation did not signal shock application.^ 



RESULTS : 

 (l) EFFECT OF SUBCUTANEOUS STIMULI (ss) 



{A) SS application. When prolonged SS were applied, extreme voltage 

 values proved inadequate: relatively low ones evoked little or no be- 

 havioural manifestations; relatively high ones produced notorious and 

 even violent signs of discomfort (cats moved and mewed continuously, 

 tried to escape and attacked cables or cage; jerks of limb, body and head 

 were prominent). Hence 'intermediate' values (1.5-15 volts) were used: 

 under these conditions, SS effects though variable, composed a list that 

 was limited and included for the group an initial startle followed by head 

 depression or rotation, ear retraction, eye closure or blinking, plaintive 

 mewing, shoulder hunching, general position shift and obvious 'concern' 

 with the excited forelimb that currently exhibited flexion jerks syn- 

 chronous w'th shocks and was regarded and/or licked. Responses usually 

 consisted in an aggregation of various individual movements, each cat 

 exhibiting a short number of characteristic combinations that could differ 

 from one animal to another. Two cats in the group responded in a stereo- 

 typed and consistent fashion to SS initiation by adopting a 'tense' attitude 

 (head depressed, ears retracted, eyes closed, body bent forward) that, 

 except for minor shifts, was maintained for the duration of SS (Fig. 2). 



Comments on the electrographic consequences of SS will be restricted 

 to general EEG effects and to potentials evoked by SS in contralateral 



^ Observations pertaining to eiTects of tone cessation in these (and other) cats will be 

 discussed elsewhere (Galeano, Roig, Segiindo and Soninicr-Smith, 1959). 



