ANALYSIS OF SOME EVOKED SYNAPTIC ACTIVITIES 425 



definition of the mode of generation and propagation of these responses and 

 the composition of different superficial axodendritic pathways, the importance 

 of developing other analytical tools cannot be overemphasized. 



One approach to the analysis of synaptic activities in superficial cortical 

 neuropil, that described here, takes advantage of the changing morpho- 

 physiological properties of developing cortex in order to provide data on the 

 proportion, magnitude and temporal relations of inhibitory and excitatory 

 synaptic activities in different superficial axodendritic organizations. This 

 approach requires first, consideration of the structural features of elements in 

 superficial cortex and of the overt synaptic activities generated therein during 

 various stages of development. These conditions are satisfactorily met with 

 favorable Golgi-Cox preparations and analyses of the generation and spread 

 of superficial negative cortical responses to local surface stimulation. Elu- 

 cidation of the distribution of inhibitory activity in overt surface responses 

 requires some method for identifying p.s.p.'s generated in distal dendritic 

 processes. Inhibitory p.s.p.'s may be identified indirectly by the effects of 

 pharmacological agents which eliminate i. p.s.p.'s in responses compounded 

 of excitatory and inhibitory activities and thereby produce profound aug- 

 mentation in the tested response (Purpura and Grundfest, 1956, 1957; 

 Purpura et a/., 1959b). 



The present report surveys recent studies that illustrate the usefulness of an 

 ontogenetic approach in analyzing the complex functional activity of the 

 cerebral cortex. The data so obtained not only serve to focus on character- 

 istics of some synaptic organizations involved in the production of different 

 evoked superficial cortical responses but also provide information on the 

 changing composition of these organizations during cortical maturation. 



METHODS 



Experiments were performed on kittens from litters born in the laboratory. 

 Attempts were made, whenever possible, to use animals from the same litter 

 at different ages. A small series of near-term fetuses were also studied. All 

 kittens were initially anesthetized with ether to permit introduction of 

 tracheal and external jugular cannulas after which the exposed skin margins 

 and scalp were infiltrated with procaine and the ether was discontinued. The 

 animals were then immobilized with succinylchohne chloride and artificially 

 ventilated. Following craniectomy, stimulating and recording electrodes were 

 placed in different arrays on the exposed suprasylvian gyrus. Stimulating 

 electrodes consisted of a pair of 100 /k. Teflon-coated wires cemented together. 

 Chlorided-silver wires with 0-2 and 0-5 mm ball tips were used for recording. 

 Monopolar differential recording was employed throughout. Other details 

 as to stimulating and recording techniques and the methods used to study the 



