266 BRAIN MECHANISMS AND LEARNING 



formation (MRF) and or mesencephalic central grey matter (MCG) (for 

 recording and/or stimulation). 



Details of electrode construction and implantation will be described 

 elsewhere (Roig, Segundo, Sommer-Smith and Galcano, to be published). 

 Main technical points were: (i) placement of recording 'cortical' and of 

 stimulating subcutaneous electrodes was controlled elcctrographically 

 until a complete response (including early positive spike and later waves) 

 occurred in the former to single shock excitation of the latter; (2) elec- 

 trodes were implanted in subcutaneous foreleg tissues and carried per- 



TEMPORAL RELATIONSHIP 



BETWEEN STIMULI 



IS ^. IS 



A) _= C) =—= 



AS SS 



IS „, CT 



B) _= « o . ^=^ D) 



E) 



AS SB 



T. 



SS SS 



Fig. 1 



TEMPORAL RELATIONSHIP BETWEEN ABSOLUTE AND INDIFFERENT STIMULI (modified from Konor- 



ski, 1948). (A) Initiation of indifferent stimulus IS followed by initiation of absolute stimulus 

 AS. (B) Cessation of indifferent stimulus followed by initiation of absolute stimulus. (C) 

 Initiation of mdiftcrent stimulus followed by interruption of feeding or of subcutaneous 

 stimulus SS. (D) Interruption of SS preceded by application of tone T; initiation of SS 

 preceded by application of a different frequency (conditioned) tone CT (see te.xt). (E) Alterna- 

 tion of subcutaneous stimulus SS and of tone T (see text). AS, absolute stimulus; IS, indifferent 

 stimulus; SS, subcutaneous stimulus; T, tone. 



mancntly by animals, thus permitting repeated excitation of same area in 

 consistent fashion (this assumption was borne out by study of evoked 

 responses, characteristics of which did not vary over weeks or months). 

 Therefore, throughout the entire procedure recordings were derived from 

 the primary cortical representation of one same excited region. 



Sessions were carried out daily in a relatively sound-proof room in 

 which animals did not see the investigator but were observed by him. 

 EEG was recorded with a Grass HID machine; amplified signals were also 

 led from after the first stage of the power amplifier (outlets fs and J6) 



