2. ELECTROPHYSIOLOGY OF THE RETINA
37
rnV
+I 0
+o 8
+0.6
+0.4
+0.2
0 -
-0.2
-0.4
,.--I( a 1
,.-.
*
.
Fig. 3. Analysis of the electroretinogram (frog) into three components: PI, PII,
and PIII. ( a ) Dark-adapted and ( b ) light-adapted. Duration of illumination shown
by a solid line at the base, 2 sec. From Granit and Riddell ( 1934).
of the retina disconnected from the brain. Kobayashi (1962) made an
extensive comparative study of fish ERGS in more than 25 species, marine
and freshwater, with special reference to ecological aspects.
B. Component Analysis of Electroretinogram
Among several attempts to analyze the ERG into components of
simpler configurations, the analysis of Granit into three components (PI,
PII, and PIII) is most generally accepted. His original analysis was performed using the cat (Granit, 1933) and frog ( Granit and Riddell, 1934),
but the result applies to other vertebrates including fish. Minor differences
between species are quantitative rather than qualitative.
As seen in Fig. 3, the PI11 is a cornea-negative potential change which
appears first following the onset of light. Shortly after the start of PIII,