J. p. SEGUNDO, C. GALEANO, J. A. SOMMER-SMITH AND J. A. ROIG 273 



ot certain previous activities as mewing, paw jerks and licking, etc. As 

 was the case with SS application, response movements evoked by SS 

 interruption were usually combined by each animal into a short number 

 of typical patterns. The two cats that responded consistently to SS 

 initiation by adopting a 'tense' attitude, reacted to SS interruption by 

 reverting to the normal 'relaxed' attitucie in an also stereotyped fashion 

 (raisnig head, elevating ears, opening eyes, straightening body) (Fig. 2). 



When SS ceased, evoked potentials naturally disappeared leaving low- 

 voltage, fast activity. 



(II) EFFECTS OF TONE (T). When the tirst T was applied alone an investiga- 

 tion reflex wdth EEG 'desynchronization' occurred (Fig. 4 — Ti). When 

 presented against a background SS, the preparation usually did not responci 

 behaviourally; late waves of evoked potentials tended to be reduced in 

 amplitude and duration (Fig. 6 — novel T). Behavioural and EEG effects 

 diminished and disappeared in the course c^f Stage I; finally, tones produced 

 little or no effect, either when applied alone or when presented against a 

 background SS (Fig. 4 — Tn; 5 — Tn). 



Thereafter (Stage II), T initiation w^as consistently tollowcd by cessation 

 of SS (Fig. I — C). During this period, animals came to react rapidly 

 (before interruption of SS) to T: percentage of positive responses in- 

 creased gradually and, in 3-10 sessions, reached and later remained at (or 

 close to) 100 per cent (Fig. 7). From a behavioural standpoint, the same 

 general comments mentioned in reference to SS application and interrup- 

 tion were applicable to T. (i) Responses to T were variable but the list was 

 limited to: hcati elevation or rotation, ear movements, eye opening or 

 blinking, body straightening (or general shift) and interruption of previous 

 activities (mewing, licking).^ This list was identical to that of SS interrup- 

 tion, (ii) Each cat associated individual movements into a short number of 

 responses that characterized that preparation (but could vary from one 

 animal to another). These compound responses to T coincided with those 

 provoked by SS interruption, (iii) In the two cats that reacted in a uniform 

 manner to SS application or substraction, T (when presented during SS) 

 also gave a stereotyped pattern that consisted in head elevation or 

 rotation, ear elevation, eye opening or bhnking, body straightening 

 (Figs. 2; 7 — Icwer graph). This pattern was identical to that produced 

 by SS interruption (Fig. 2). 



Tone initiation became capable also of modifying potentials (EP) evoked 

 by SS on contralateral sensory cortex. Effects consisted in reduction 



^ As far as exclusively (and obviously insutficieiu) visual observation is concerned, limb 

 jerks were not modified by T. 



