INHIBITORY INTERACTION IN THE RETINA 



247 



Fig. 4. Electron micrograph of eccentric cell axon (E) and branch (B). The axon 

 and bundle of axonal branches are enclosed by a basement membrane and a thin 

 layer of Schwann's cell cytoplasm. The nucleus of the Schwann's ceil is 



labeled (Nii). 



neighboring a particular ommatidium results in a fixed decrement in the 

 frequency of discharge of that ommatidium. irrespective of its own level of 

 excitation. These basic properties of the inhibition have been described in 

 detail in an earlier paper (Hartline et al., 1956). 



Not only can inhibition be exerted by normally induced activity in the 

 nervous pathways from regions neighboring an ommatidium. but antidromic 

 stimulation of the optic nerve fibers from these regions also produces a slowing 

 in the discharge rate from a test ommatidium (Tomita, 1958). The inhibition 

 thus produced is similar in all of its aspects to that produced by the illumina- 

 tion of neighboring receptor units: the slowing is greater the higher the 

 frequency of the antidromic volleys, and the larger the number of fibers 

 recruited by submaximal shocks of increasing strength. Figure 8, showing the 

 inhibition in response to trains of antidromic volleys, is noteworthy in showing 



