382 



BRAIN MECHANISMS AND LEARNING 



a tracheotomy was performed under ether anaesthesia and the animal 

 placed on flaxedil and artificial respiration. Local anaesthesia was used for 

 the scalp incision, the hemispheres were widely exposed and the pia 

 arachnoid covered with warm mineral oil. At the end of the experiment 

 the isolated regions were serially sectioned to confirm the completeness of 

 loss of neural continuity. The pial circulation was, of course, preserved 

 intact in these preparations. The appearance of the whole brain at autopsy, 

 as well as a cross section through the isolated region, are indicated in 

 Fig. 7. 



Fig. 7 



Whole brain at autopsy and cross section through tlie isolated regions. The defect in tlie right 



frontal pole was produced in the course of removal of the brain at autopsy. 



Gross electrodes were placed upon the surface of the isolated mirror 

 region and adjacent surrounding cortex and one to four tungsten micro- 

 electrodes (Hubel, 1957) were inserted into the isolated slab at a depth of 

 500 to 1000 micra. Search for spontaneously firing units was rarely 

 successful so that one had to rely upon multiple placement at a depth 

 where unit discharge might reasonably be expected in connection with 

 surface electrographic paroxysms. A pledget of metrazol placed upon 

 adjacent normal cortex elicited a seizure discharge which slowly spread 



