Spike Train Statistics from Empirical Facts to Theory: The Case of the Retina - Modeling in Computational Biology and Biomedicine - page 255

a b

A On-center ganglion cells B Off-center ganglion cells

off area
(center)
On area
(surround)
Light on

On area
(center)
off area
(surround)

- +

- - + +

++ --

- - + +

+ -

- - + +

- +

L ight on

1
Cent ral
spot

2
Perpheral
spot

3
Central
illumination

4
Surround
illumination

5
Diffuse
illumination

0 0.5 1.0 1.5

s

(b-1) (b-2) (b-3) (b-4)

Fig. 8.3 Center-surround antagonism ( a ) Illumination of a piece of retina (Created by A.G.
Palacios). ( b ) ON-center and OFF-center RF (Figure from [ 1 ]). The first line shows center-surround
architecture of the cell while lines 2-6 shows a typical response of the G cells and the illumination
pattern leading to that response. ( b-1 ) Center-surround architecture of an ON-center cell and
illumination pattern. ( b-2 ) Time duration of the stimulus and spike response of the cell. Time
is in abscissa. ( b-3 )and( b-4 ) Same as columns ( b-1 )and( b-2 ) for an OFF-center cell. Case 1
left ( right ) is a ON-center (OFF-center) G cell where a light spot ( yellow )inthecenteroftheRF
generates an increase (decrease) of spike firing. In case 2 a spot stimulus in the surround generates
a decrease (increase) of the spike rate. In case 3, 4 an increase in the size of the stimuli leads a
sharper response. In case 5 a diffuse stimulus covering the center-periphery has no effect on the
spike firing rate

On the opposite, the illumination of the photoreceptors at the periphery of the
RF results in a hyper-polarization of OFF B cells so in a decrease of spikes rate
in the respective connected G cells. In more general terms, as a consequence of
this architecture (Fig. 8.3 a), a G cell connected to that B cell fires spikes at the
maximal rate when the center of the RF is illuminated and when the surround is
dark (Fig. 8.3 (b-2), case 3). On the opposite it fires no spike at all when the center
of the RF is dark and the surround is illuminated (Fig. 8.3 (b-4), case 4).
Figure 8.3 b summarizes the different patterns of illuminations—G cell response
in terms of spike firing and the functional implication of RF organization. For
example, a full, uniform, illumination of the RF leads to a regular spiking activity
with no difference between ON-OFF and OFF-ON cells (Fig. 8.3 b, case 5).
As consequence of dynamical and complex interaction (spatial and temporal)
opposite functions for, e.g., color, contrast, intensity are likewise found for a single
G cell, depending where the stimulus is present in their RF.