J. p. SEGUNDO, C. GALEANO, J. A. SOMMER-SMITH AND ). A. ROIG 285 



application and simultaneously with the potential drop in CSC, other 

 areas frequently showed EEC 'arousal'. 



Therefore, T probably operated by way of a process inducing EEG 

 'activation' and acting predominantly upon the somatic sensory cortices. 

 All EEG 'activating' influences of this type are not necessarily identical, 

 however, and may perhaps be separated on the basis of other criteria as 

 intensity and distribution of EEG 'arousal', types of concomitant modifica- 

 tions in cortical evoked potentials and behaviour, etc. In these experiments, 

 effects of tones reinforced by cessation of painful stimuli were compared 

 with consequences of other EEG 'arousing' agents, applied in similar 

 circumstances and, if various criteria were taken into account, global 

 responses were indeed different. Firstly, dissimilar behaviour resulted from 

 causes affecting evoked potentials in a similar manner: novel tones pro- 

 duced minor investigation reflexes; intense sounds, startle patterns; tones 

 conditioned to SS initiation were inoperant during SS; MRF excitation 

 was sub-threshold for visible effects; T produced 'anticipatory' effects 

 described above. Secondly, ability to produce EEG 'arousal' and capacity 

 to affect EP were not exhibited in a quantitatively parallel fashion by 

 various agents: evoked potentials responded little or irregularly to novel 

 tones, 'conditioned' tones or intense sounds that determined clear-cut 

 'activation'; they reacted markedly to T or to MRF excitation.^ Finally, 

 inffuences compared here differed in regional selectivity, either provoking 

 generalized (MRF excitation ; novel tone ; intense sound ; conditioned tone) 

 or localized (conditioned tone) effects. T itself w^as not consistent in this 

 respect: an important fact, however, was that masking of potentials (in 

 contralateral sensory cortex) definitely could be associated with restricted 

 EEG 'arousal' (present in CSC, HSC and NMDT; absent in acoustic and 

 visual cortices, MRF and MCG). Further signs of topographical specificity 

 issued from comparison of somatic sensory and visual effects of T: 

 modification of subcutaneously induced responses (somatic sensory 

 cortex) could take place without concomitant alteration of photically 

 evoked potentials (visual cortex). 



In short, and to summarize, the electrographic ability acquired by T 

 (through association with substraction of SS) consisted in a capacity to 

 mask somatic sensory cortical evoked potentials in an intense and fre- 

 quently restricted fashion; such blocking seemed associated with a simul- 

 taneous and similarly distributed EEG 'activating' influence. Localized 



1 Blocking of cortical potentials during EEG 'arousal' has been known for some years; 

 augmentatory effects have been reported recently (Bremer and Stoupel, 1959; Dumont and 

 Dell, 1958; Gauthier, Parma and Zanchctti, 195O; Segundo, Sommer-Smith, Galeano and 

 Roig, 1959)- 



