588 BRAIN MECHANISMS AND LEARNING 



spinal cord (WyckofFand Young, 1956) and brain (Green and Maxwell, 

 1959; Luse, 1959) to be completely occupied by glial tissue through which 

 all ionic and respiratory exchanges must occur. It is in the investigation of 

 such factors as these that the structural or functional changes induced in 

 'memory traces' may, perhaps, be found to lie. At least, such factors may 

 play a significant role in the genesis of the rhythmic hippocampal slow- 

 wave trains so closely related to the learning process. 



ACKNOWLEDGMENTS 



The studies described here were assisted by Grants B-1883, B-610 and 

 B-611 from the U.S. Public Health Service. 



