434 



BRAIN MECHANISMS AND LEARNING 



ill three or five superimposed sweeps. One concentric electrode consisting 

 of 32 gauge enamelled stainless steel wire enclosed within a 22 gauge 

 stainless steel sheath was placed stereotaxically in the brain stem reticular 

 formation. Bipolar stimulation was performed between the tip of the 

 inner conductor and a bare collar of 0.5 mm. wide encircling the lower 

 end of the insulated sheath. The distance between the tip and collar was 

 approximately 1 .0 mm. The electrical stimuli were short square waves of 



Fig. I 



Diagram showing the experimental arrangement. 



0.2 msec, duration, i/sec, voltage variable, delivered by a Grass stimulator 

 through an isolation unit and preceding the skin stimulation at intervals 

 of 100 and 50 msec. Tactile stinuilation was apphed to hair-covered areas 

 of the right foreleg by a small camel's-hair brush mounted on a lever 

 rigidly attached to the moving armature of an electromagnet device the 

 coil of which was energized by a pulse of 4 msec, duration, i/sec. by way 

 of a Grass stimulator. The main features of the experimental arrangement 



