J. p. SEGUNDO, C. GALEANO, j. A. SOMMER-SMITH AND J. A. ROIG 279 



Ti ; 6 — second line), (iii) Effects ot loud crashing noises resembled diosc 

 of T (Fig. 6 — diird line), (iv) In two cats training involved use of different 

 frequency tones, one (conditioned tone CT) indicating SS initiation and 



EFFECTS ON POT. EV. BY SS ON CSC 

 I. T 



sil 



II. MRF SUM 



15V . I - 200 



CONT 



STIM 



t ^t 



/ V 



fSjfV^^ 



05 V 



Fig. 10 

 comparison of modifications produced in evoked potentials: 



I, tone; II, MESENCEPHALIC RETICULAR FORMATION STIMULATION (pulse 



duration, o.i msec; frequency, 200 c.p.s.). Modifications induced on 

 evoked potentials by T or by 0.75-1.5 volts were comparable; stimu- 

 lation with o.s was ineffectual. CC^NT., control. 



the Other (T) signalling SS cessation (Fig. i D) : the latter T acquired an 

 intense capacity to affect behaviour and evoked potentials (w^hcn applied 

 during SS). The former became conditioned in the current sense produc- 

 ing behavioural and EEG effects (startle, leg retraction, 'activation', etc.) 



