BEHAVIOURAL AND EEG EFFECTS OF TONES 

 'REINFORCED' BY CESSATION OF PAINFUL STIMULF 



J. P. Segundo, C. Galeano, J. A. Sommer-Smith and J. A. Roig 



Major contributions to the neurophysiology of learning have issued from 

 the study of so-called 'signal responses' established by way of systematic 

 association of two stimuli (one indifferent, one effective), a combination 

 leading frequently to a change in responses provoked by the former 

 (Anokhin, 1957; Pavlov, 1941). In most work, initiation of the indifferent 

 (later conditioned) stimulus IS was followed, after a brief interval, by 

 initiation of the absolute excitation AS (Fig. lA). It has been suggested 

 and/or established that other combinations also are useful: for instance, 

 tone cessation — pain initiation (Fig. iB), tone initiation — cessation of 

 eating, etc. (Galeano, Roig, Segundo and Sommer-Smith, 1959; Konorski, 

 1948; Rowland, 1957; Segundo, Roig and Sonnner-Smith, 1959; 

 Zbrozyna, 1958; Zeleny cited by Pavlov, 1951). In the present series, a 

 brief indifferent tone was systematically followed by cessation of a pro- 

 longed painful stimulus SS (Fig. iC) : this routine was capable of inducing 

 a learning process and animals came to respond bchaviourally (in a 

 manner similar to the effect of pain substraction) and electroencepha- 

 lographically (with reduction of sensory cortical potentials) to tones 

 treated in this fashion. 



material and methods 



Experiments were performed upon seven cats carrying electrodes 

 unplantcd chronically in: (i) subcutaneous tissue of foreleg (for stimula- 

 tion) ; (ii) extradural space overlying both somatic sensory and, some- 

 times, one acoustic and/or visual cortical receiving areas (for recording) 

 (these leads shall be referred to as 'cortical') ; (iii) subcortical structures as 

 nucleus medialis dorsalis of thalamus (NMDT), mesencephalic reticular 



1 This work, published in abstract fashion in the XXI Physiological Congress Volume 

 (Sommer-Smith, Galeano, Roig and Segundo, 1959), was supported in part by grants from 

 Rockefeller Foundation (58122) and U.S.A.F. Office for Scientific Research (AF49-638-585). 



265 



