J. p. SEGUNDO, C. GALEANO, J. A. SOMMER-SMITH AND |. A. ROICi iH} 



Other Structures (acoustic cortex, visual cortex, MRF and MCG): in 

 frequent instances, typical effects occurred on CSC and little or no altera- 

 tion took place in the other regions. 



Tones reinforced by cessation of SS and capable of provoking EEG and 

 behavioural effects described above when applied against a background 

 SS were usually also effective when presented alone. Though behaviour- 

 ally responses were poor (minor shifts, investigation movements), tones 

 consistently produced EEG 'arousal' generalized or localized to CSC 

 (Fig. 4 — TCESS 1 80, a). Another characteristic EEG effect was a relatively 

 delayed (initiation 10-30 seconds after T) and prolonged (10-30 seconds) 

 discharge of large voltage and slow (4-14 c.p.s.) waves and spindles that 

 followed hiitial 'desynchronization': this effect was noticeable even it T 

 was presented against a background 'desynchronized' tracing (Fig. 4 — T- 

 CESS SS 180 b). 



When habituated, T initiation had no obvious consequences; after 

 training (and against relatively slow background EEG) it eliciteti an 

 evoked potential, specially noticeable on CSC, MRF and MCG. 



In two animals, T was applied (with no previous SS) during natural 

 sleep (behavioural and EEG). Responses were cither absent or conhned to 

 slight and transient EEG 'desynchronization'. Hence tones associated with 

 shock cessation lacked arousing potentialities of sounds reinforced by 

 other absolute stimuli (e.g. SS initiation, brain stem excitation) (Rowland 

 Segundo, Roig and Sommer-Snnth, iQsy). 



DISCUSSION 



Chronological relationship is critical when 'neutral' and 'biologically 

 significant' stimuli are paired with the purpose of establishing a learned 

 response. Efficacy of certain temporal sequences (tone initiation — feeding 

 or pain initiation; tone cessation — pain initiation) has been widely con- 

 firmed (Pavlov, 1941; Rowland, 1954; Segundo, Roig, Sommer-Smith, 

 1959; Zeleny cited by Pavlov, 1941, etc.). Contrastingly, usefulness of 

 other alliances (e.g. feeding — tone initiation, backward conditioning, 

 etc.) has been less convincing (Zbrozyna, 1958). Conceivably, application 

 of yet other possible patterns (e.g. tone initiation — cessation of absolute 

 stimulus) might also develop novel (learned) responses to previously 

 indifferent stimuli (Konorski, 1948). Experimental observations have 

 supported this assumption: if each time a sound was applied food was 

 withdrawn forcibly from an eating dog, animals eventually stopped eating 

 on presentation of the auditory stimulus in spite of continued availability of 

 aliment (Zbrozyna, 1958); in backward conditioning (rats) indifferent 



