582 



RADIATION BIOLOGY 



of the nervous system. Visual photochemistry provides the starting 

 point for this type of analysis. The great tool for attacking the rest of 

 the problem is that of recording, by electronic devices, the electrical 

 signs of each part of the visual system. This type of research could 

 scarcely have been undertaken until the late 1920's, when the necessary 

 equipment first became readily available. Since that time a relatively 

 small number of laboratories have taken up the slow and technically 

 difficult task of placing electrodes (see Fig. 13-1) at various locations 



— / 



(a) (d) 



Fig. 13-1. Placement of electrodes for recording electrical responses of the eye. In 

 each drawing A is an active electrode, and I is an indifferent electrode, (a) Electrodes 

 in position for recording the human action potential by the use of a contact lens, (b) 

 Connections with an excised eye for measuring the resting or action potential, (c) 

 Top view of arrangement for recording impulses from a single fiber dissected out from 

 the optic nerve of Limulus. (d) Side view of arrangement for recording impulses from 

 a fiber dissected out from a vertebrate retina. 



within the visual system. The resulting data, summarized in this chap- 

 ter, represent pioneer research in this field. There is reason to believe 

 that this somewhat bewildering array of findings may soon yield the basis 

 for more realistic interpretations of visual phenomena about which there 

 has been seemingly endless speculation. 



This chapter will survey the field of electrical phenomena, including 

 the resting potential of the eye; the retinal action potential, or electro- 

 retinogram; the responses of optic nerve fibers; records from the optic 

 thalamus and cortex; and effects produced by electrical stimulation of 

 the visual system. It is not possible within the space allotted to give a 



