  We consider a model of basic inner retinal connectivity where bipolar and
amacrine cells interconnect, and both cell types project onto ganglion cells,
modulating their response output to the brain visual areas. We derive an
analytical formula for the spatio-temporal response of retinal ganglion cells
to stimuli taking into account the effects of amacrine cells inhibition. This
analysis reveals two important functional parameters of the network: (i) the
intensity of the interactions between bipolar and amacrine cells, and, (ii) the
characteristic time scale of these responses. Both parameters have a profound
combined impact on the spatiotemporal features of RGC responses to light. %We
show that, depending on these parameters value, retinal ganglion cells can
change their spatio-temporal response (e.g. from monophasic to biphasic). The
validity of the model is confirmed by faithfully reproducing pharmacogenetic
experimental results obtained by stimulating excitatory DREADDs (Designer
Receptors Exclusively Activated by Designer Drugs) expressed on ganglion cells
and amacrine cells subclasses, thereby modifying the inner retinal network
activity to visual stimuli in a complex, entangled manner. Our mathematical
model allows us to explore and decipher these complex effects in a manner that
would not be feasible experimentally and provides novel insights in retinal
dynamics.
