R. W. DOTY AND C. GIURGEA I35 



The cortex is stimulated through platinum electrodes, usually resting 

 on the pial surface or just beneath it although in some dogs the thickness 

 of the skull made such adjustment difficult. Two of four electrodes are 

 carried in 7 mm. diameter plastic buttons which are held in trephine holes 

 by means of screws (Doty, Rutledge and Larsen, 1956). Flexible 0.5 mm. 

 diameter polyethylene insulated wires connect the electrodes to an 1 8 or 

 34 contact receptacle permanently secured to the skull by stainless steel 

 posts (Doty, 1959). 



Stimulation consists of i msec, rectangular current pulses at a frequency 

 of 50/sec. and is monitored on a cathode-ray oscilloscope with a long- 

 persistence screen. Great care is taken to keep the stimulating circuits and 

 the animals isolated from ground and to avoid any other possibility of 

 stimulation outside that intended. 



Prior to pairing CS and US the effects of stimulation are observed for 

 each electrode pair. It is advantageous to have several pairs of electrodes 

 in 'motor' cortical areas so that the chances are increased for procuring a 

 relatively simple movement to serve as an UR. By means of automatic and 

 silent control the CS is presented for 3-4 seconds and is slightly overlapped 

 by the US of 1-1.5 seconds duration. Six to ten combinations of CS and 

 US are made daily. 



After study of CS-US coupling is complete, the animals are trained in 

 the same experimental chamber to press a lever to obtain food. The lever 

 is then connected to administer cortical stimulation with each press. 



RESULTS 



Doi^ Alplhi. All stimulatit)n in the 'motor' cortical regions produced 

 stiff, complex and unnatural movements. That finally chosen as an UR 

 was a lifting and extension of the right hind leg, a slight lifting and curling 

 of the tail, and a rotation of the head to the midline and down (Fig. 1). 

 The US was 1.8 mA. applied just posterior to the left postcrucial sulcus. 

 The CS of r.i niA. was applied to the left posterior suprasylvian gyrus. It 

 elicited no response for the first forty-two CS-US pairings. The CS 

 current was then increased to 2.2 mA. and elicited an opening of the eyes 

 and turning of the head to the right, a response judged to be inherent to 

 stimulation of this area. It was still obtained, when, later in the experiment, 

 the CS was again reduced to i.o mA. The first distinct CR was seen on the 

 thirtieth post-operative day after 108 CS-US pairings. It was a turning of 

 the head to the midline and down, a movement similar to the head move- 

 ment seen to the US and in opposition to that inherently evoked by the 



