NEURAL ACTIVITY IN THE RETINA 



69/ 



FIG. 3. .1. Retina of the dog showing cone axons (n); rod axons (A); types of bipolars (c-c). of 

 which e is Ramon y Cajals cone bipolar; ganglion cells (m, n); ascending nerve fiber 0); and cen- 

 trifugal fibers (j). B. Details of structure of ganglion cells (B, C and E") and of connections made 

 by centrifugal fibers (a). [From Ramon y Cajal (123).] 



animals). The ERG was discovered by Holmgren (94, 

 95). The literature has been twice summarized by the 

 author (69, 73), the first time with a full historical 

 review. Some of the more important classical papers 

 are those of Kiihne & Steiner (102, 103), Gotch (60, 

 61), Piper (119, 120, 121), Einthoven & Jolly (53), 

 Frolich (56), Chaffee et al. (31), Chaffee & Hampson 

 (32), Hartline (85), Adrian & Matthews (3) and 

 Kohlrausch (98). 



The ERG (which in such animals as cats and frogs 

 reaches maximal cornea-positive values around i mv) 

 begins with a small negative dip, the a-wave, then 

 goes positive, the 6-wave. If stimulus intensity is suf- 

 ficiently high, there follows a very slow cornea-positive 

 secondary rise or c-wave and, at the cessation of il- 



lumination, another positive hump, the off-effect or 

 (/-wave (see fig. 4). There is some doubt as to whether 

 the c-wave occurs in cone eyes. In mixed eyes it is not 

 found in the state of light adaptation (144). Noell 

 (114) appears to hold that it is always present but 

 sometimes compensated for i3\ an opposite negative 

 potential of similar slow characteristics. There is no 

 reason to believe any of the ERG waves to be absent 

 in any kind of vertebrate eye; but they are very dif- 

 ferently developed with respect to .size and rate of rise 

 and they vary with the experimental conditions so 

 that, for instance, in rod eyes the (/-wave is small or 

 missing. The ERG has generally been thought to 

 consist of components integrated in complex inter- 

 ference pictures. These are reasonably well-known 



